The Great Preamp Survey (Vol. 1, No. 1, Jan/Feb 1977)

Part I: In which we compare the sound of 22 preamplifiers (or 23, depending on how you count it), come to some reasonably firm conclusions, and begin our search for a sonically correlatable electronic test.

---------------

There can be no doubt about it, preamps are the hot button in audio perfectionist circles today. The gradual realization that money can't buy happiness in this particular product category (or at least doesn't guarantee happy results) and that even the most advanced designs all sound different is causing considerable head-scratching and opinionated expertizing throughout the land.

It would stand to reason if the low-level amplification stages in a modern reproducer chain were its most flawless links. No moving parts. No current to speak of. None of the problems of the megahertz regions. Nothing but the simplest low-frequency voltage-amplifier circuitry. Engineers outside the audio field can't even understand what all the fuss is about. "What's the matter with you guys?" is their common reaction.

The matter is that to raise the amplitude of a 3-millivolt signal coming out of a phono cartridge to the 1 volt or so needed to feed a power amplifier takes a gain of some 51 dB.

Add to that an extra 19 dB for RIAA equalization at 20 Hz and you've got a hell of a big climb. All kinds of bad things can happen to a supposedly perfect analog signal on the way there. And do. A significant portion of the inaccuracies we hear in phono reproduction is definitely traceable to the preamplifier. (One of our technical consultants has been saying for years, with characteristic candor, that 'all preamplifiers are shit.') We at The Audio Critic wanted to get this irritating problem out of our way as early as possible, so we decided to do it more or less in one gulp and review every preamplifier that's even halfway promising in our first issue, with maybe a few stragglers to catch up with in the second issue-and that's all. That way we'd have a good starting point for a reference system and would need to test state-of-the-art contenders only one by one as they came along. Then we could devote our energies to the really fascinating problems such as speaker systems.

We soon found out, though, that pre-amplifiers and their design philosophy can be almost as fascinating, not to mention controversial.

The easiest way to get them was the hard way.

First we had to get all these preamps together in one place. Because you can't com pare the sound of something like, say, the Mark Levinson JC-2 and the DB Systems preamp by testing one in August and the other in November. Until we could choose a clearly preferred reference preamp, we wanted all units to be available in both the listening room and the laboratory simply by reaching for them. Right then and there.

Since we knew it would take up to a year before we could get that many different units on loan from their manufacturers, we went ahead and bought them all. (To be exact, 20 out of the 22.) It was a hard decision to make, since a lot of money was involved (we aren't exactly Consumers Union), but we finally had to make the investment just to get the show on the road.

We want to emphasize that this wasn't a policy decision to keep The Audio Critic pure; it's very difficult for a manufacturer to "tweak" a preamp made with high-tolerance components even if he knows it's going to a re viewer. (It isn't like a tape recorder, with a large number of factory adjustments; a preamp is basically as good or bad as its circuit design.) We would have been perfectly willing to borrow the equipment, as we'll be willing in the future, but we're committed to six issues a year, and the stretchability of our deadlines has limits.

So whatever benefits resulted, both in anonymity and in run-of-the-factory sampling, were purely incidental. As a matter of fact, we carried on a lively dialogue with a number of top designers to find out about their theories, if any, even though we had bought their equipment in a store without their knowledge. (More about that under the individual model descriptions.)

In the laboratory, everything was too perfect.

As we explain elsewhere in this first issue, our tests must be regarded as work-in-progress.

We report six times a year all we have found out until deadline time. We trust, therefore, that our subscribers won't be too upset to learn that in Part I of this preamp survey we have no sensational laboratory test to report that correlates perfectly with sonic performance. It should be some consolation that the top preamp designers haven't found such a test, either. (But see Andy Rappaport's letter farther below for an implicit suggestion of one.) We're working very intensively on this problem and should have some interesting things to report in Part II of this survey, in our next issue. Meanwhile, the laboratory situation looks like this:

All of the preamplifiers tested appear to meet their specs comfortably. The trouble is that there's no correlation between the standard specs and listening quality.

For example, harmonic distortion is simply nonexistent in these preamps. That includes the best and the worst-sounding ones. Our spectrum analyzer will quickly pinpoint any harmonic up to 50 kHz of greater amplitude than about -86 dB relative to the fundamental, which comes to 0.005% distortion. The residual distortion of our oscillator throughout the audio range is about the same. Sweeping through these units at various frequencies hardly ever showed the slightest blip, and even in the rarest cases nothing worse than 0.01% at several volts out. To link any audible unpleasantness to these figures would be cultist nonsense, especially since they invariably related to lower-order harmonics. (So help us, we never, never saw a fifth or a seventh harmonic blipping out of the -86 dB noise floor of the analyzer, despite the claim in the Mark Levinson JC-2 literature that this is where their circuit is superior to others. Too bad. That looked like a promising test.) As for intermodulation distortion measurements, the SMPTE method (60 Hz and 6 or 7 kHz, 4:1) is clearly a waste of time on present-day equipment, as even Matti Otala (the Father of TIM) strongly implies in his latest paper. We quickly dispensed with that one. The CCIF method (two high frequencies 1 kHz apart, 1:1) has, on the other hand, served us well in other tests; but in the case of the 22 preamps-forget it. They passed the CCIF test just as easily as the THD test. Even with various high-frequency test signals spaced only 100 Hz or 50 Hz apart.

We had an amusing experience in connection with this type of test when a very hip young circuit designer was passing through town and visited our lab. We both shared a rather low opinion of the Dynaco PAT-5 preamp (it did poorly in our listening tests), but when he was told that this preamp measured as clean as a whistle he wouldn't believe it. Okay, he said (with the "wise guy" vocative unspoken but implicit), let's feed 19 kHz and 20 kHz into the phono input, one to one.

We did, and there was nary a blip on the spectrum analyzer. No sidebands at 18 kHz and 21 kHz; no difference product at 1 kHz. "There's something wrong with your spectrum analyzer" was his last resort. Whereupon we increased the input until the PAT-5 went into hard clip ping at God knows how many volts out and the CRT display bristled with spikes. The spectrum analyzer was working fine. He walked out of the lab muttering to himself.

Checking the RIAA equalization accuracy proved to be just as unproductive. All of the pre amps, good or bad, were accurately equalized.

By that we mean within +/-0.75 dB or better, from 20 Hz to 20 kHz, which is good enough to eliminate the possibility of listening preferences on that score. Even the phono cartridge we used in the tests could have varied that much from day to day, owing to temperature and humidity changes. We're well aware of the +/- 0.2 dB cult (or is it +- 0.25 dB?), whose adherents are convinced that any greater RIAA-cum cartridge deviations will destroy the validity of A-B testing, but we found cruder audible differences from preamp to preamp than could be rationalized by such obsessions. In most cases we didn't change our listening preference between two preamps A and B even when we advanced or cut back the tone controls a notch on A only or B only! Hum and noise had equally little to do with our listening preferences, although some of these preamps are both measurably and audibly quieter than others, and we note out standing cases under the individual model headings. But the remarkable Rappaport PRE-1, for example, hummed more than it should have, and we'd still rather listen to it any day of the week than to, say, the Yamaha C-2, which was unbelievably quiet.

Phono input overload was our last hope among the more or less standard specs. There was a time, not so long ago, when only a few circuit designers were paying sufficient attention to this and the results showed it. But in the case of the thoroughly up-to-date preamps we're dealing with here, we could establish no correlation between the sine-wave over load figure and sonic performance, undoubtedly because the figure was never low enough to be a problem. There were some outstanding units (e.g., Advent Model 300) of the 100-mV-is good-enough school (at 1 kHz, that is); other great-sounding ones like the Paragon Model 12 proved only that a much higher figure, like chicken soup, can't hurt. We defy any one to predict the sound of a phono circuit from its input overload spec, as long as it isn't ridiculously low, which nowadays it apparently never is.

During the past year or so, a number of unconventional preamplifier tests have been proposed, mainly by audio people in the Boston area. Preeminent among these is Tomlinson Holman, whose amazingly good, inexpensive phono circuit for the Advent Model 300 receiver certainly makes him a preamp guru to reckon with. His paper on the subject in the May 1976 issue of the Journal of the Audio Engineering Society is required reading for the serious student of preamplifier behavior.

Holman's first test is for ''cartridge 99 inductance interaction." He proves, with irrefutable argument and documentation, that a preamplifier exhibiting perfect frequency response when driven from a voltage source can still have all sorts of horrible rises and droops at the higher frequencies when driven from an inductive source, such as the equivalent electrical circuit of a typical phono cartridge. Since correct input stage design can completely eliminate these high-frequency interactions, the test is undoubtedly useful for nailing un sophisticated circuitry, but it didn't help us in our search for the electronic cause of sonic differences. We found that, when a preamp sounded lousy, it kept sounding lousy even after we had switched to a completely noninductive source like a high-quality pre preamplifier fed by a moving-coil cartridge.

Besides, as we explain below, the regular magnetic cartridge used in our listening tests had negligibly low inductance.

The other unconventional test proposed by Holman (whose paper also covers a lot of interesting ground we're bypassing here) is the measurement of the spectral content of square waves passed through the preamplifier after suitable RIAA preemphasis (to simulate the pre-equalized response of LP records). Since a square wave is theoretically the sum of an infinite series of odd harmonics of diminishing amplitude, the presence of even harmonics in the output is evidence of a form of transient distortion, which can be quantified on a spectrum analyzer. This is very different, as you will note, from the square-wave tests generally seen in the commercial hi-fi magazines, where they show you an oscilloscope (i.e., time domain) photograph of a square wave fed through the high-level "aux" input of the preamp. (The phono input is nearly always neglected because, for some reason, these people don't own an RIAA preemphasis network.) We're intrigued by the Holman square wave test, which seems to pinpoint various asymmetries in the circuit characteristics, as well as slew-rate limiting. So far, however, we find it more useful for nailing an occasional baddie (not consistently, though) than for any kind of quantitative distinction between good, better and best. For example, the most irritating-sounding preamp in our entire survey, the BGW Model 202, did quite poorly on this test, but no sooner did we say "Aha!" than the almost equally irritating Marantz 3600 measured 16 to 18 dB better. And our old friend, the Dynaco PAT-5, which in some ways we liked even less than the BGW and the Marantz, did incomparably better than either.

On the other hand, the best-sounding pre amps all did well, so there may be some correlation; however, they didn't come out in the same order on the test as on listening preference, so there's really no fine-tuned correlation. Another highly active and enlightened Boston practitioner, Alvin Foster, has already published Holman square-wave test results on a number of preamps included in our survey here, and we see the same pattern: good checks out better than bad, but best doesn't necessarily check out better than good. Since we don't believe in re-measuring what other testers whose reliability we have no reason to question have already measured, we'll let this subject simmer on a back burner for a while, at least until we're able to have a more positive attitude toward it. We're certainly of no mind to publish detailed charts of our findings. On top of it, we've heard it rumored that Tom Holman him self no longer has confidence in this test. If that's true (we must emphasize that we didn't hear it from him directly), the whole matter may benefit from "benign neglect." The above-mentioned Al Foster has also come up with a quantitative test of his own.

He measures the output level where the preamp begins to clip at three different frequencies:

1 kHz, 10 kHz and 50 kHz. Ideally, he claims, all three clipping levels should be the same; however, if the 50-kHz clipping level is at least 50% of the 1-kHz level (say 4 volts or better at 50 kHz when it is 8 volts at 1 kHz), the preamp will sound "excellent" and indistinguishable from all others that pass this test. On the other hand, if this reading is 30% or less, the preamp will sound ''veiled," according to Al. This seemed almost too good to be true, so we tried it-and it was too good to be true. For example, the D B Systems preamp and the Luxman CL-350 both did brilliantly on the test (the D B scored 91% and the Luxman 100%), yet the D B sounded unequivocally better. And the Rappaport PRE-1, which sounded even better than the D B (by a narrow margin but consistently), failed the test with a vengeance. There went another neat little trick.

It seems to us, since both the Holman square-wave test and the Foster clipping test are essentially measurements of slew-rate limiting from two different points of view, that slew rate affects sonic performance in a more round about way than is generally assumed to be the case. Quite possibly, slew rate has no significance as an absolute quantity and matters only with regard to the compatibility (or inter face) of cascaded amplifier stages. (Again, we refer you to the Rappaport letter.) We shall have more to say on this subject as we gather further evidence.

There are many more tests still to be explored.

There's no doubt in our mind that a sonically correlatable electronic test, or combination of tests, can and will be found one day. (Not necessarily by The Audio Critic, though.) Just as in the cruder days of audio THD and IM were correlatable quantities, with improved sound resulting from their reduction, today's more subtle and elusive distortions should also prove to be quantifiable and eventually controllable.

We plan to spend time in the laboratory on a number of promising new tests, including Matti Otala's "'sine-square" distortion test for TIM (we have already experimented with it on power amps but ran into some minor difficulties), Wayne Hetrich's highly intriguing gated asymmetry test (presented last October 29th to the AES convention), possibly some form of the square-sine-square test suggested in the Rappaport letter, an investigation of the effect of continuing the RIAA equalization well beyond 20 kHz, and several others.

Meanwhile, let's get down to what it's all about in the end. The sound.

The listening tests.

Before you can begin to test preamplifiers by listening to them, you have some sort of faith in the ability of the human ear to detect very small differences in sound. That faith, founded on repeated experience and constituting the very essence of audiophilia, is occasionally undermined by simplistic come-on you-guys-they-all-sound-alike generalizations, sometimes even from sources with high credentials. One recent example was an audiophile talk show on WBUR, Boston University's public service FM station, featuring as guest speaker another well-known Boston audio mafioso, Mark Davis, who has something to do with psychoacoustics at MIT. Mark, a circuit designer himself, flatly asserted that all pre amps sound alike, from the two-transistor phono circuit in the General Electric transistor manual to the most elaborate audio freak unit money can buy, as long as certain conditions are met. These include exact matching of volume levels on A-B comparisons, no more than typically low THD and IM distortion, accurate RIAA equalization and, most important in his opinion, low phono input capacitance, which must be lowered if it's too high in order to prevent cartridge interactions that would invalidate the comparisons.

We're prefacing our explanation of our listening tests with these remarks (even though we have already covered the above criteria, except volume matching, and obviously arrived at totally opposite conclusions) just to make two points.

One is that it matters a great deal who does the listening. We, too, could have assembled a listening panel of reasonably intelligent, music-loving persons who wouldn't have heard the difference between the Mark Levinson JC-2 and the Dynaco PAT-5. The world is full of them. Some of them even know a great deal about electronics. (See also our remarks in the introductory article in this issue.) It takes a rather special listening attitude, not to mention experience, to sit through long-suffering comparisons of closely matched equipment and slowly but confidently zero in on the differences.

We believe our staff is good at it, but we have very little faith in statistical surveys ("19 persons preferred A and 22 preferred B"). If value judgments of sensory perceptions could be arrived at that way, Johnny Walker would use census takers instead of professional tasters. We have a feeling that Mark Davis might have come to a different conclusion with a different selection of listeners.

Our other point is that highly exacting listening tests must be performed by inserting the device under test into an extremely high quality system. The speakers, especially, must be the kind that are hard to please. The AR box speakers used in the Mark Davis tests are much too forgiving. That may be a good thing when you're trying to enjoy the music from a less-than-perfect program source. For preamp testing, forget it. We're probably dwelling on a perverse opinion at greater length than it deserves, but when we heard the hosts of the talk show conclude the discussion by chortling that another audio myth bites the dust, we got upset. (After all, impressionable young people were listening.) Which brings us to our own unforgiving speaker system, the Dahlquist DQ-10. We used it for these tests, not because we think it's the world's best (we haven't decided yet what is), but because it mercilessly shows up the slightest flaws in the electronics behind it.

A pair of DQ-10's, in combination with a pair of DQ-IW subwoofers, biamped with two Quatre DG-250 Gain Cell (analog multiplier) power amplifiers, was the reference system on which all the final conclusions of this survey are based. (See our Dahlquist DQ-10/DQ-1W report elsewhere in this issue for a rationale of this system.) Other power amplifiers we used, mainly to test compatibilities, included the Yamaha B-2 and the GAS Son of Ampzilla;

in the early weeding-out phases of the survey we also used the DQ-10's without subwoofers.

Our "electronic crossover" was particularly suitable for these tests in that it was actually non-electronic: a simple RC network inserted between the preamp under test and the two power amps, so that no additional active stage could add its own sound to the chain.

(Again, see our Dahlquist report for details.) The turntable used was the Luxman PD 121; the arm was the Formula 4, which turned out to be just a little too low in mass for ideal compatibility with our reference cartridge, but we left it alone after the tests were under way in order to maintain the constants of our survey unchanged. The choice of reference cartridge was, of course, the most important decision, and we finally selected the Grado Signature Model One by a process of elimination.

Initially, our leanings were strongly toward one of the better moving-coil cartridges, but we soon discovered that the insertion of an additional component between the cartridge and the preamp, namely a transformer or a pre preamp, would make our evaluations much more prone to error. It's a considerably more straightforward process to judge A against B than A + C against B + C. Only about one third of the preamps tested are available with their own moving-coil electronics (either built in or as an accessory); some of these have al ready been checked out with a Denon DL-103, and a separate report on their performance with various moving-coil cartridges will follow in Part II of this survey in our next issue (March/April). The only common denominator of all these preamps, however, is the "mag phono" input, so we decided we had to use a magnetic cartridge if we wanted to test them all identically.

Once that decision was made, the selection of the Grado became logical. It has by far the lowest inductance (55 millihenries) of any magnetic cartridge known to us, so the whole problem of cartridge inductance interactions is rendered irrelevant. With any phono input capacitance or tone-arm lead length this side of insanity, the Grado behaves electrically as a voltage source. This enabled us to concentrate on the inherent listening quality of each preamp circuit without the nuisance of "tuning" cable lengths, soldering capacitors in and out, etc.

Furthermore, the Grado Signature Model One is a superior cartridge sonically, quite regard less of its electrical characteristics. Its smooth ness and resolution of detail at the higher frequencies are second to none, making it an excellent tool for pinpointing small differences in preamp accuracy.

On this reference system, every member of our staff could hear distinct differences between any two preamps in our test, in a few cases only after prolonged and careful A-B-ing, in most cases instantly and with ridiculous ease.

We adjusted our methodology accordingly. With 22 units you have to remain flexible because, theoretically, you could end up with 231 separate, rigidly controlled A-B tests if you decided to test each of them against each of the others. That would have made about as much sense as setting up a formal blind tasting of 22 wines that included Gallo Hearty Burgundy as well as Romanee-Conti 1945. Since we had no intention to rank all these units from first place to 22nd, we could be more relaxed in our approach. We were interested in establishing only two rankings: the best-sounding preamp regardless of price and the best buy for the money. So the baddies could be quickly eliminated without any fuss and without trying to find out by endless testing which was the least bad.

Having all units available to live with on a prolonged basis made our job much easier than is usually the case in audio reviewing.

We never had to wonder whether what we were hearing was as good as what we had heard six weeks earlier. The other unit was still there to be inserted into our reference system in a matter of minutes. It was as if, instead of being asked to judge a beauty contest, one had a chance to live in the same house with all the contestants for a few months. The choice of winners would become a lot easier.

Before you allow that thought to inflame your imagination, let us tell you how we A-B-ed the serious contenders. We have some rather strong opinions on A-B testing, and they all relate to our determination to zero in on audible differences in sound, no matter how small or insignificant, rather than to prove the fallibility of the human ear. Rapid A-B-ing is just great for the latter. Take two pieces of equipment that you know sound indisputably different after months of living with both, put them on an A-B switch, match your volume levels carefully, and yank the switch back and forth every few seconds while the music plays on. Lo and behold, A and B sound exactly the same. Not because there's no audible difference between them but because your ear tends to integrate the sound under these conditions. Now try listening to A for five minutes, stop for a moment (anywhere from ten to thirty seconds), go back to the same segment of the music, and listen to B for five minutes. The differences will be readily apparent.

We absolutely refuse to do any rapid A-B-ing when we're fine-tuning our perception of two components that are fairly close in quality. We invite comment on this from our subscribers (as, of course, on anything else within these pages), but it will take a lot of powerful persuasion to change our mind. Relatively long stretches of A and B on the same music, with a moment of silence between the two, is a procedure that has so far resulted in unanimous agreement among our staff members on the relative merit of every unit tested.

We're satisfied that our method works.

A word about matching volume levels.

Obviously, if A is distinctly louder than B or vice versa, you can't make an accurate judgment between two units of closely matched quality. (Between, say, the Mark Levinson and the BGW it doesn't make a damn bit of difference. You'll know which is better even if you listen from the shower.) We made an effort to match our volume levels within 1 dB or so on all the more demanding comparisons, by means of a 1 kHz tone on a test record and a quick meter reading. We made no attempt to match levels within 0.2 dB or 0.3 dB or anything of the sort, even though we're well aware that it's de rigueur according to the rapid-A-B cult. This is one of those alienated elecro-techno-freak fantasies that bear no relationship to the practice of music in the real world. Real-world musicians aren't "flat" like signal generators and meters. They can't control their output within

0.2 dB from note to note and bar to bar. Even one of those supersmooth, pearly runs on the piano by, say, Arturo Benedetti Michelangeli will fluctuate more than that in volume. So if you cut into the music with your A-B switch and the level changes by 0.2 dB after the cut, it may be either because A and B aren't perfectly matched in gain or because the performance has changed that much in level. You'll never know the difference: the net result is exactly the same. In audio testing, it some times helps to think musicians instead of millivolts.

We must keep emphasizing that, after months of steady exposure to all these preamplifiers, an intense preoccupation with methodology seemed to us pretentious, pedantic and a waste of time. We ended up knowing how each of them sounded, regardless of how we went about our listening. For that reason, we were also fairly casual about blind testing. The initial exposure of a staff member to a new piece of equipment nearly always took the form of a blind A-B test against an already familiar unit, mainly because it was more fun that way. But after everybody's preferences were fairly well established and it came to sorting out the finer points of difference, we paid very little attention to ''security." The units were there on the shelf for anyone to look at. We firmly believe that all of us are objective and mature enough not to "want" a particular brand to sound better than another; that's kid stuff. And, again, from the point of view of ascertaining reality rather than the fallibility of the human ear, it helps to know that this is the Yamaha C-2 with the brittle highs we all heard yesterday; other wise we would have to reestablish the same fact under a different blind code name today and possibly become confused because we might be less alert today than we were yesterday. Retained information can only help realistic testers; in the final analysis, elaborate blind and double-blind testing is a shell game played with your perceptions by withholding information.

The source material.

One of the main problems in testing preamps (as against, say, microphones) just by listening to them is that you must start with a vinyl groove. Since there's no way of determining objectively what that groove holds in the way of total aural information, there's no way of judging the accuracy of the preamp in any absolute sense. What if the preamp cancels out inaccuracies in the groove by introducing equal and opposite inaccuracies, making the music sounds more natural than it would through another, more accurate preamp?

Here we really think that statistics be come useful and valid. If a preamp makes fifty different records sound cleaner, more open, more detailed, more natural than other pre amps, it's obviously a great statistical unlikelihood that this preamp "zigs" in distortion whenever each of the fifty records "zags." For that reason we used a good many records of at least a dozen different labels to arrive at our conclusions. Of course, we had some favorites: a few recordings are so specific in certain aspects of their sonic character that they make particularly convenient tools for testing.

We went back again and again to the Messiaen "Quartet for the End of Time" on RCA (see also our Records and Recording column), the Bernstein "Carmen" on DGG, the "Siegfried" sung in English on EMI (not Angel!), the complete Prokofiev "Romeo and Juliet" ballet on London, the Copland "Billy the Kid" on Turnabout, Cat Stevens' "Tea for the Tillerman" on Island (not A & M), Pink Floyd's "The Dark Side of the Moon" on EMI Harvest, and (inevitably) the Sheffield Labs and Japanese Audio Lab records, dreadful as they are in musical content.

In addition, Associate Editor Max Wilcox contributed a few test lacquers cut from master tapes he had microphoned, produced, edited and mixed himself. That, of course, pro vided a particularly good fix on the original sound, without the usual uncertainties about the degree of accuracy represented by the groove.

Someone may ask at this point, what about other program sources such as a tuner or tape deck? Didn't we test the high-level inputs of these preamps? No, we didn't. We were testing phono preamps. If you never play phonograph records through your stereo system, you need only a source selector switch plus a good attenuator, not an expensive pre amp. If we call the phono stage P and the high level stage H, we were testing the accuracy of P + H. In some special cases we also tested P alone. But never H alone. We really couldn't care less which preamp has the most accurate H, all by itself. It's academic. We were trying to find the one with the most accurate P + H.

If a slightly less accurate H is fed by a vastly superior P to produce the best P + H, overall, that's one we want for our reference preamp.

What about other preamps beside these 22 (or 23)?

Obviously, we couldn't swallow the whole world in our first issue (although we tried).

As it is, this is by far the broadest critical survey of preamps ever published anywhere, at least to our knowledge. We used two criteria in assembling this group. One was the posture taken by the manufacturer. If it was suggested anywhere in the manufacturer's literature or advertising that "This is it!", that he offered the preamp as the best there is, or equal to the best, or state-of-the-art, or what have you, we tried to include that unit. Our other guideline was the prevailing climate of opinion among audio perfectionists, both amateur and professional. If we perceived that a unit is widely believed to offer outstanding performance, we tried to include it whether we agreed or not.

Our rationale for inclusion is given under the individual model listings below, unless it's self explanatory.

Even so, we missed a number of models we would have liked to include, and we're taking steps to obtain them for testing at the earliest opportunity. We're particularly interested in the Bravura, the Dayton Wright SPL Mk 2b, and the Trevor Lees kit, since each of these has been reported from supposedly credible sources to be state-of-the-art. Others that deserve to be investigated are the CM 300, the Dunlap Clarke, the Infinity FET (although we hear mixed comments about it from the field), the SAE Mark 2100, the Soundcraftsmen, and probably a few others that have some how eluded us. We'll make an attempt to test them all.

(FLASH! Near press time we're pleased to report that we have received the Trevor Lees kit, including all the latest mods, and that we plan to assemble it and test it in time for a report in Part II of this survey.) You may have noticed that the only Japanese preamplifiers we have included are the audiophile-oriented brands: Luxman, Marantz, Stax and Yamaha. (We missed the Accu phase, an omission that ought to be rectified.) Sony, Pioneer, Sansui, Kenwood, and Technics by Panasonic were omitted, even though they make high-priced preamps, because it was our judgment that these models represent a marketing decision by these companies to round out their commercial hi-fi lines on the high end rather than a sudden dedication of their efforts to the needs of audio perfectionists. We cannot conceive of any of these units as challengers that might change our rankings here. If we ever receive evidence to the contrary, we'll rush into print with it without the slightest hesitation and with profound apologies.

And now-the individual reports.

Advent Model 300

Advent Corporation, 195 Albany Street, Cambridge, MA 02139. Model 300 FM Stereo Receiver, $259.95.

Three-year warranty; manufacturer pays return freight.

Tested #J0 02876, owned by The Audio Critic.

The very first unit in our alphabetical listing will recoup the subscription cost of The Audio Critic many times over for anyone who is looking for the greatest per-dollar value of all time in preamp performance.

The Advent Model 300 isn't even a pre amplifier, but who cares? For $260, you get a neat little FM tuner and a 15-watt-per-channel power amplifier thrown in free of charge. We haven't tested these, but we can assure you that they work. The Editor's two young sons are blasting away with our expropriated 300, straight through, even as these lines are being written.

The only reason for the inclusion of the Advent 300 in this survey was the announcement ad from Advent that asserted that the 300 incorporates '"'an entirely new phono preamp section that is audibly equal or superior to any separate preamp at any price." While we find ourselves unable to endorse that claim without any qualification, we must report that it's far from the usual advertising bombast and is substantially truthful. Only a small handful of the preamps we tested come even close to the Advent when you convert it to a separate pre amplifier by removing two thick, U-shaped aluminum jumper wires in the back of the receiver. As we hint on our front cover, the Advent sounds better than, for example, the Yamaha C-1 at $1800.

We still can't recommend the Advent to those who want absolutely the best, regardless of price. While completely open, free, neutral, and non-fatiguing in sound, with excellent depth perspective and very impressive dynamics, the Advent still doesn't possess the ultimate refinement of inner detail audible on the top four or five units in our survey. It would be grossly unfair to pit the Advent against each of these.

freckle by freckle and eyelash by eyelash, since even the cheapest of them costs almost twice as much. What's more, even their narrow margin of superiority must be somewhat qualified.

Whatever slight blunting or veiling of detail the Advent may produce (and we must emphasize that it's very slight) is due, in our opinion, to the tone control circuit, which can- not be switched out. This is the feature we liked least about the unit; in fact, we discovered in the lab that when the tone controls were set for dead-flat response on the right channel, there was a 2 dB bass boost on the left channel. Furthermore, the dead-flat position of the treble control was a few minutes past the 12 o'clock position. (Of course, we musn't forget that we're dealing with a $260 stereo receiver here; it's really a schizophrenic situation! Next thing you know, we'll complain that the controls don't have that expensive feel. They don't, damn it . . .) The point we're trying to make, though, is that when you bypass the tone control circuit and the volume control by testing the Advent at "tape out," unbelievable things begin to happen. We absolutely drove our keen-eared Associate Editor up the wall by going from those "tape out" jacks into the "remote phono" inputs of the Mark Levinson JC-2 and A-B-ing the phono stage of the Advent against the JC-2's own phono stage. He couldn't decide which one he preferred! After a long evening of agonizing reappraisal, we came to the reasonably firm conclusion that we preferred the JC-2 with its own phono stage. It seemed just the slightest bit higher in resolution of inner detail. Whew! About the only thing to add is that the Advent Model 300 has rather low gain when used as a separate preamp, preferring to see a power amplifier with an input sensitivity of 1 volt or even less. And that all the lower-priced preamps in the world are dead, dead, dead.

AGI Model 511

Audio General, Inc., 1631 Easton Road, Willow Grove, PA 19090. Model 511 Stereo Preamplifier, $400. Three year warranty, manufacturer pays two-way freight.

Tested #5460051, owned by The Audio Critic.

This one gave us a hard time because, good as it is, we expected it to be even better. There's something about the AGI 511 that has great intellectual appeal to the audio purist. It's a stripped-down, strictly functional unit, without tone controls, filters or other frills, but very sturdily built, with obviously high-quality parts.

(For example, the power switch that supplies current to the convenience outlets in the back is rated at 15 amps and will handle 20. You can plug in your monster amplifier. And the countersunk machine screws that hold the top 14 and bottom covers in place are made of un strippable stainless steel. We could go on and on.) Most important of all, the circuit philosophy is all-out, obviously with nothing but the advanced audiophile in mind, and the gorgeous circuit board seems to reflect this. It all looks like a real bargain at $400.

We have met Dave Spiegel, the designer of the 511, and can vouch for his utter dedication to the noncommercial, purist approach in engineering. He is even into Fourier analysis, and who in the audio industry goes even near that stuff? (Don't say Dick Heyser; he isn't a manufacturer.) So we really expected the world of this preamp and were somewhat disappointed when we got a little less.

The sound of the AGI is very smooth and free of distortion, against a very quiet back ground-definitely an audiophile's kind of sound. But when you listen for depth perspective and, in general, any kind of spatial information, there are problems. When the program material contains highs, the sound becomes more spacious, but the highs appear to come forward instead of being heard in correct perspective within the sonic fabric.

When there are no highs, the overall sound stage seems to become smaller, as if somehow the ceiling had been lowered. When A-B-ed against a preamp that is flawless in this respect, such as the Rappaport PRE-1, the AGI has a closed-down, darker sound by comparison. On recordings particularly rich in depth information, such as the English "Siegfried" on EMI, the AGI creates constant ambiguities as to what's up front, what's in the middle and what's all the way in the back. These effects are of course slight (after all, this is still a superior preamp), but they're there all right and don't really change as you experiment with cartridges, power amps, etc.

We have a feeling we know what's wrong with the AGI 511, but we can't be absolutely sure. It may be that the 250V /uS slew rate of the phono stage (something of a world's record) is too fast for driving the high-level stage, which has a slew rate of only 30V /uS. The result could be some form of TIM. This is still frontier stuff (at least to us poor audio slobs, in case some NASA types are listening in) and remains to be verified.

Meanwhile, we have to rate the AGI Model 511 as the least satisfying in sound among the few really good preamps we have tested.

Audio Research SP-3A-1 Audio Research Corporation, 2843 26th Avenue South, Minneapolis, MN 55406. Model SP-3A-1N High Definition Stereo Control, $795. Five-year warranty (vacuum tubes, two years); customer pays all freight. Tested #570290-1A-1, borrowed from owner.

When we started this survey, we weren't even going to include the SP-3A-1, as we had heard it would be discontinued once the SP-4 was phased in. Besides, it had been the Editor's reference preamp for almost two years, long before The Audio Critic was conceived, and we really didn't think it would stand up under competition with the latest solid-state con tenders for state-of-the-art. (We weren't far wrong.) As soon as we found out that the Audio Research vacuum-tube line would be continued as long as there was a demand for it, we borrowed this fairly late production sample (made in December 1975). It incorporated all the modifications that had made the life of SP-3A-1 owners so eventful over the years, except the July 1976 mod (involving the removal of one pair of resistors and two pairs of capacitors), which even the factory contends is exceedingly subtle in effect. Since we didn't want to touch a borrowed unit with a soldering iron, and since the shortcomings of its sonic performance weren't all that subtle, we decided not to bother with this latest mod.

Well, what about the good old SP-3A-1? It's still as ugly as we remembered it, the controls are still as Mickey Mouse as ever, and the midrange is still as gorgeous as ever. Holy smoke, what a midrange! If the female voice is all you ever listen to, with maybe a few soft instruments plinking away in the background, this might still be the best preamp for you.

Just for that, however, it's a little bit overpriced. But talk about depth and dimensionality. . . ! On complex, dynamic material, on the other hand, the SP-3A-1 had a distinct

"electronic" glare under the scrutiny of our merciless reference system. (We have a feeling that the Magneplanars the ARC people sharpen their ears on are a lot kinder, though probably not quite as truthful, as the Dahlquist DQ-10's.) The clashing cymbals and clacking castanets of Carmen, for example, just didn't sound as nice as on a number of other preamps, both solid-state and vacuum-tube.

Nor did the violins. Not that the glare, or call it over-brightness, that we complain of had anything to do with the typical, cheap, transistory nastiness. This was still a "soft" vacuum-tube sound overall, but with a slightly unnatural, even unmusical, treble coloration.

We're aware that we're not the only ones to have noticed the SP-3A-1's slight garishness in the upper ranges. (The tubes, incidentally, were from Amperex, made in Great Britain.) Even the ARC people must have decided some time ago that the honeymoon was coming to an end and that it was time to begin the development of something like the SP-4.

All in all, we feel that the Audio Re search SP-3A-1, like Joe Louis, should have gone into retirement while still the invincible champion.

Audio Research SP-4

Audio Research Corporation, 2843 26th Avenue South, Minneapolis, MN 55406. Model SP-4 High Definition Preamplifier, $695. Plug-in head amp (not yet avail able), $150. Three-year warranty, not clear whether customer pays all freight. Tested #76402005, owned by The Audio Critic.

Editor's Note: As most of our subscribers know, this is the unit we delayed publication for. When our sample was finally delivered, just a few days before the end of the year and almost two months later than promised, we were very close to going to press, so that our comments else where in this survey don't fully reflect the sub sequent influence of the SP-4 on our opinions.

We had to make a few editorial changes in various parts of our report for the sake of clarity, but they are few and far between. For that reason we have inserted the SP-4 review in its proper alphabetical sequence here, in the hope that the reader will keep our statements about it in mind when reading the remaining 18 reviews.

Our first impression of the SP-4 after unpacking it and listening to it for a few hours was: This is the one. The winner. Although, as you will see below, that wasn't our ultimate conclusion, our enthusiasm will be appreciated by anyone who has seen and heard this beautiful piece of equipment. Even if it isn't the undisputed winner of our survey, it's a winner.

The SP-3A-1, with the tremendous ac claim it had received over the years, was a hard act to follow, and Audio Research would have been guilty of a real marketing blunder if they had stepped out of their role as the vacuum tube hard-liners of the industry for the sake of anything less than an extraordinary solid-state product. Well, the SP-4 is no marketing blunder. In fact, it's a very clever bid for the Mark Levinson end of the audiophile market (especially now that the JC-2 costs almost twice as much as the SP-4), while hanging in there with the vacuum-tube crowd by retaining the SP-3A-1 in the line. A real pincer movement.

But the SP-4 is certainly no SP-3A-1 to look at. It's as sexy as can be. The 19-inch brushed-aluminum relay-rack-type front panel sports two large black handles. The rotary switches and controls are cylindrical with slightly squooshed-in sides, just asking to be fingered. The toggle switches are long, skinny isosceles triangles of aluminum, and when you operate them they go ""snick" like the gearshift on a BMW 630CSi. The crackle-finished chassis suggests battleship-like solidity. Any audio freak who isn't turned on by all this has some thing wrong with his hormones.

As for the sound, the SP-4 has absolutely the un-canniest clarity of detail of any preamplifier we've ever heard. On a flamenco guitar recording, for example, even the fastest pas sages are completely unblurred, with every little pluck standing out in bold relief and with a distinct mini-moment of dead silence between plucks. It's somethin' else. Unbelievable spaciousness, too. The sound stage is a mile wide and the ceiling is a mile high. Front to-back depth is outstanding. (This is beginning to sound like a rave review, which it isn't.) So what's wrong? It took us almost two weeks to discover what. The bass, first of all.

It's there, all right, which is why we lived with it quite happily at first, but gradually we realized that it was lacking in dynamics.

For example, those low string bass slams on Cat Stevens' ""Hardheaded Woman" just didn't have the impact that makes them so exciting through the Rappaport PRE-1 and the Mark Levinson JC-2. This absence of genuine sock was also clearly evident on the London re cording of Prokofiev's "Romeo and Juliet," where the bass simply wipes you out on the other two preamps. And let it be quite clear that we aren't talking about boom. We miss those real, low-down, dull thuds on the SP-4.

The other major problem is more subtle and became apparent only after prolonged A-B-ing of the SP-4 with the Rappaport, our overall top choice in this survey. The SP-4 definitely had sharper delineation of inner detail, which at first gave it the appearance of greater transparency. But in the end this sharpness turned out to be just that. Sharp. The detailing was at the expense of a slight hard ness and sibilance that eventually caused listening fatigue. By comparison, the Rappaport didn't make all the little clicks, snaps, taps, hisses and fricatives in the music quite as astonishingly clear, but they were embedded in the overall sonic fabric in what we judged to be a more accurate, true-to-life perspective.

Quite aside from its superior bass, the Rappaport was just sweeter and somehow more musical, while still clearly reproducing all the detail that was actually there. We must add that this was by far the most difficult A-B test in our entire survey, really the only one that baffled us for any length of time. These are two great sounding preamps. What's more, the SP-4 is certainly the better built of the two (second to none, in that respect, except maybe a brick outhouse), as well as lower in hum and noise.

We also have a suspicion that the SP-4 might have given an even better account of itself on a reference system with a higher tolerance for hardness and other sonic irritants than ours. The Dahlquist DQ-10's are unable to forgive even the minutest amount.

Since the SP-4 undoubtedly received its factory shakedown through the new Audio Research D-100 power amplifier and Magneplanar speakers, it would certainly be worthwhile to audition it that way. We intend to do so at the earliest opportunity. This isn't a disclaimer of the validity of our test; what we found out was reality all right. But sometimes 100% reality is less agreeable than 98%.

And what about the Mark Levinson? We found the JC-2 to be as noticeably superior to the SP-4 in bass impact as the Rappaport and possibly even more so in non-fatiguing, nonirritating long-term performance. But switching from the Audio Research to the Levinson resulted in an almost startling collapse of the space in which the music was located, as if the total sound stage had been reduced to half its width, height and depth.

This, of course, is the Achilles heel of the JC-2 and the main reason why we must rate the Rappaport over it in combination with most power amplifiers (not all, though). The Rappaport and the SP-4 are rather closely matched in spaciousness, with the Rappaport possibly a bit more stable and definite in the spatial location of instruments and voices. These three units constitute the current elite of preamplifiers in our opinion, and the audio perfectionist owes each of them the more careful attention.

A word about the Analog Module, which is Audio Research's trade name for the epoxy-encapsulated amplification stages in the SP-4 (as well as the D-100). In their pro motional literature, ARC attempts to suggest that the Analog Module is a new and fourth amplification concept after the vacuum tube, the bipolar transistor and the FET. We found it peculiar that no startling new inventions in this area have been reported in the technical press, yet here's a small company already using it in a highly developed application. We called up ARC, identified ourselves, and tried to obtain some information, without the least success. They're being very cagey about this, ostensibly to prevent cheap commercial imitations, but our impression is that they consider the resulting aura of mystery to be good for business. Nowhere in their literature do they use the words "solid state" (they refer to the Analog Module as a device that acts as a

"super tube"); in fact, it's our distinct impression that they wouldn't mind some speculation among the fans that maybe thar's wee little tubes in them thar modules. (Nuvistors? No way. Not at this price and not in those tiny capsules.) We'll take an educated guess here, mainly in the hope of smoking out the old foxes in Minnesota. The Analog Module, friends, is nothing but an IC. A very good one, maybe with some sophisticated new wrinkles, but still a chip. Or group of chips, if Frito-Lay should insist you can't have just one. Audio Research claims a gain-bandwidth product in excess of 10 MHz for the Analog Module, as well as less than 0.05 to 0.5% THD or IM distortion before feedback. There are some nice new chips that meet those specs, and there's no reason why Honeywell, ARC's subcontractor for these modules, couldn't do a real job with them.

Those guys are really good.

If this is all hogwash, all that Audio Research has to do is write us a letter denying that there are IC's in there, and we'll print it in boldface. We don't claim infallibility, but neither do we have much patience with artificial mysteries.

Meanwhile, congratulations to Bill John son and his crew on a very impressive job.

BGW Model 202

BGW Systems, PO Box 3742, Beverly Hills, CA 90212. Model 202 Stereo System Control Center, $599. Warranty not clear from material enclosed with original factory container. Tested #760418, owned by The Audio Critic.

This one is a disaster. The reason for its inclusion here was the tone of various BGW spec sheets, which make fierce noises like "no compromise design effort . . . new techniques had to be found . . . significant improvements to conventional preamp design . . . unsurpassed performance . . ."-you get the idea. It ain't so.

The BGW 202 had the hardest, most irritating, most ear-distressing sound of any pre amp in this survey. As soon as we turned it on, anyone near the listening area would inevitably say, "What is that? Will you please turn it down!" After that, it mattered very little that the unit is well built, has extremely flexible and nice-to-handle controls, and can provide very impressive amounts of gain. Just in case it may cross your mind that we had a defective unit- we didn't. We measured low distortion, ac curate RIAA equalization; only the Holman square wave test was rather bad (but see our earlier comments anent the Boston tests).

In view of this company's proudly advertised share in supplying the sound system for the movie Earthquake, we can't resist remarking that, for $599, we expected something more earthshaking.

Editor's Note: Close to press time comes word that the price of the BGW 202 has been lowered by $200. How come, fellas? Was there any thing wrong with it?

Dayton Wright SPS Mk 3

Dayton Wright Associates Limited, 350 Weber Street North, Waterloo, Ont., Canada N2J 4E3. SPS Mk 3 Professional Preamplifier, $525. Tested #3457. on loan by courtesy of The Listening Room, Scarsdale, NY.

Anything from Dayton Wright is strictly for the audio purist; we only regret that it wasn't the top-of-the-line SPL Mk 2b that we obtained for testing, since it's advertised as "a refined and developed SPS type circuit" plus pre-preamplifier. Well, here's the unrefined SPS, and it's damn good.

This is a tone-controlless, basic preamp a la AGI or D B, perhaps a little eccentric in physical design with its brick shape, an un usually small front-panel area, and all inputs and outputs on top, but we still rather liked its visual and tactile characteristics.

Its sound is good enough to have made us think, when we first turned it on, that this might be it--the best of them all. It didn't quite end up that way, but that doesn't make the SPS any less smooth, natural and detailed in sound. It's definitely of audio-freak caliber.

We would rate it somewhat above the AGI, for example; maybe just below the D B (the D B seemed to give our final top choices closer competition on direct A-B testing) and some where in the same league with the GAS Thaedra, though we'd be inclined to favor the latter if pressed for a decision.

As you can see, we don't feel very strongly about any negative characteristic of SPS. The 'eliminator' that removed it from our group of finalists was the Rappaport PRE-1. Compared to the Rappaport, the Day ton Wright seemed slightly darker, heavier, less spacious in sound. Front-to-back information wasn't quite as explicit. Nothing really disturbingly worse, just not quite as good.

Here was one isolated case where RIAA equalization error may conceivably have contributed to the slight fault we heard. Relative to 1 kHz, the EQ was off by +1 dB at 40 Hz and -0.5 dB at 5 kHz, so that the response with RIAA preemphasis was a straight slanting line between these frequencies, steadily tipping up toward the bass end but still fitting into a +0.75 dB strip. Could that have caused the slightly "chocolaty' sound, as one of our staff put it? It's possible, but we doubt it. (At the higher frequencies, the response tipped up again slightly, reaching +1 dB at 20 kHz. Strange.) In any event, if this is only Dayton Wright's second-best preamp, their best must be awfully good, and we can hardly wait to test it.

D B Systems DB-1/DB-2

D B Systems, PO Box 187, Jaffrey Center, NH 03454.

DB-1 Precision Preamp, $350, with DB-2 Power Supply, $75. Five-year warranty; manufacturer pays return freight. Tested #1080624/#2180521, owned by The Audio Critic. Backup samples #1271128 / #2271128, on loan from manufacturer.

There's no justice in the world. Until just a few months ago, the D B was probably the world's most accurate preamp for anything less than the insane price of the Mark Levinson JC-2. A super product and a great bargain as well. Suddenly, there are the Rappaport PRE-1 and the Audio Research SP-4, which we're virtually certain haven't even been seen yet within the walls of the D B company. And there's also the Advent 300 for 39% less than the D B. Here are some nice people in New Hampshire doing absolutely the right thing and, boom, the roof caves in. That's show biz.

(You don't think audio is show business? You're dead wrong.) Even today, if we were forced to name the most accurate preamp for no more than $500, we'd have to say the D B. The most accurate, mind you. The prettiest-sounding might well be the GAS Thoebe or even the Advent. And not for $575, mind you. You can get a Rappaport PRE-1 for that.

Of course, the D B is a diminutive, tone controlless, basic preamp without any frills (except some rather nice filters, low and high), so you might not think that $425 is such a fantastically low price for it. But it's beautifully made, with very high-quality parts, no conventional wiring (everything is buttoned down on printed-circuit boards-the back panel itself is one of the boards!), and very ambitious circuitry. We have spoken to Dave Hadaway, the D B's designer, on several occasions, and it's quite clear to us that he is a relentless perfectionist who believes in eliminating any kind of distortion or inaccuracy that can be measured in any way, without arguments as to its audibility or lack thereof. With the D B, you are in deepest audiophilia. :

The sound of the DB is extremely clean, open and neutral, with excellent transient detailing, good depth perspective, and perhaps just a slight lack of low bass impact. (That last observation is somewhat paradoxical, since the D B is one of the few preamps whose measured response goes way down into the subsonic region, so this is something we'll have to look into once more, in Part II.) In direct A-B comparisons it lost out to both the Rappaport PRE-1 and the Mark Levinson JC-2, in each case after some hesitancy on our part. Com pared to these two pre-amps, the D B seemed a touch more "transistory" in quality, with the upper midrange somehow more forward and aggressive. It just isn't quite as classy a sound-but it's a small difference. The GAS Thaedra also sounded sweeter, rounder, some what more spacious-in a word, prettier-but we weren't convinced that it was letting as much information through as the D B. The latter is a warts-and-all reproducer.

We also did a quick check on the D B using its own pre-preamp (DB-4, $150) and a Denon DL-103. Its relative ranking with respect to the Mark Levinson (with System D) and the Thaedra (with its own head amp) remained about the same. More about this in our detailed pre-preamp and head amp report in Part II.

If none of this sounds sufficiently enthusiastic, let us conclude with the statement that we'd be perfectly happy to live with the D B on a permanent basis if these other pre amps didn't exist. The D B may not be absolutely the best there is, but it's certainly good enough for anyone, including us.

Dynaco PAT-5

Dynaco, Inc., Coles Road & Camden Avenue or PO Box 88, Blackwood, NJ 08012. PAT-5 Preamplifier (factory wired), $399. One-year warranty; manufacturer pays return freight. Tested #33544867, owned by The Audio Critic.

It's one of life's great mysteries to us why this preamplifier should have any standing in audiophile circles. But it does. Again and again, we see both editorial comment and letters about it in publications that ought to know better, referring to it as close-to-the-best-for-less. Maybe it's the Volkswagen syndrome; more than a few VW owners like to fantasize that, after all, they're driving something not far removed from a Porsche.

Well, the PAT-5 is very far removed from a Mark Levinson. Overall, we'd rate it as the poorest-sounding preamplifier in this survey.

It has a pinched, hashy, edgy, nontransparent, transistory quality that's neither accurate nor musical. A staff member, having been told by another that the PAT-5 at least didn't stick needles in your ear like the BGW202 or the Marantz 3600, said: "Oh, but those two still have some class. This one sounds like a kitchen radio." A small exaggeration, but indicative of the relative ranking of the PAT-5.

Again, we must point out that we weren't listening to a defective unit. In fact, we were amazed in the laboratory how impeccably the PAT-5 measured in every respect. (See also our earlier comments on the lab tests in general.) About the only thing we can think of to explain this vast discrepancy between our findings and those of others (who aren't, after all, deaf) is that Dynaco's large volume may require the substitution of "equivalent" circuit components from various suppliers as they start new production runs. And these supposedly equivalent IC chips, transistors, capacitors, or what have you, may, in reality, add up to a different sound at the output than the last set of components. It's just a wild guess, but not nearly as wild as the sound of the PAT-5 we tested.

Epicure Model Four

Epicure Products, Inc., One Charles Street, Newbury port, MA 01950. Model Four Stereo Preamplifier, $450.

Five-year warranty; not clear who pays freight. Tested #10313, owned by The Audio Critic.

Two things attracted us to the Epicure preamp, prompting us to include it in this survey. One was that, even though it's a big, bulky black box, it weighs absolutely nothing. Light as a feather. This smacked of high technology.

The other was the owner's manual we had seen, which talked engineering and "state of the art" page after page after page. Even the TIM test with the 500 Hz square wave and 6 kHz sine wave was there (probably taken from the Tektronix 5L4N literature)-but only through the high-level stage! Anyway, this was one we had to try.

It was a waste of time. The only thing that can be said for the Epicure is that it doesn't sound downright unpleasant like the BGW 202 or the Marantz 3600. It won't drive you out of the room. Its style is unaggressive.

But it sounds completely inaccurate and un musical. Closed-down, nasal, honky. Our Associate Editor illustrated its sound by cup ping both hands in front of his mouth and nose, and continuing to talk that way.

We really have nothing further to say about the Epicture except possibly to exclaim with Elton John: "Get back, Honky Cat!" GAS Thaedra/Thoebe The Great American Sound Co., Inc., 20940 Lassen Street, Chatsworth, CA 91311. Thaedra Servo-Loop Preamplifier, $909. Five-year warranty; customer pays all freight. Tested #500790, later replaced by #500961, owned by The Audio Critic. Thoebe Servo-Loop Pre amplifier, $509 (not tested separately).

This is the unit you can count as two units, in which case our survey covers 23 preamplifiers. The manufacturer declares that

"Thoebe shares with Thaedra identical servo loop electronic circuitry and sonic performance," and we have no reason to doubt his word. So, to test the mag-phono sound of this product, we only listened to Thaedra. Our conclusions should apply equally to Thoebe.

Dealers in the field have by and large con firmed this claim of equivalence-on mag phono only. With a moving-coil input, the signal travels through two stages in Thaedra, as against three stages in Thoebe with its accessory head amp Goliath. This makes Thaedra a theoretically more sophisticated preamplifier for moving-coil cartridges, a point that will be explored in greater detail in Part II of our survey.

Thaedra will undoubtedly be considered the finest preamplifier money can buy by a considerable number of audio enthusiasts, and we know that nothing will change their minds, not even our disagreement with that ranking. This preamplifier always sounds beautiful. It never does anything nasty; never sounds hard, edgy or transistory; always gives you a nice sense of space around the instruments or voices; at the same time, it's absolutely clean, transparent and grainless. In a solid-state unit, it gives you everything you always liked about tubes and most of the things you always liked about transistors. Unfailingly musical, too; it's impossible to be an audiophile and dislike Thaedra.

Nevertheless, we don't consider this pre amplifier to be 100% accurate. When Thaedra gets zapped with a hard but clean transient, it sort of wraps it in whipped cream instead of letting it through hard and clean. There's an ever-so-slight rounding of sharp corners, a taming of spikes and bristles, that many musical ears may even find a welcome relief from the aggressive quality of typical transistor preamps.

The point is, though, that the Mark Levinson JC-2, the Rappaport PRE-1 or the Audio Research SP-4 aren't typical transistor preamps. When the whole orchestra digs into a fortissimo chord, with a downstroke of the bows, these preamps reproduce it the way you hear it in the concert hall. With a clear-cut snap. Through Thaedra it's a slightly spongy thud. Same thing on piano reproduction. The impact of the felt hammers on the strings is softened by Thaedra; a Steinway begins to sound like a Baldwin, all velvet glove and no iron fist.

We're virtually certain that this type of sound is what the designer of Thaedra prefers; it didn't just come out that way as a result of some abstract circuit philosophy. It's a for matted sound, deliberately created to appeal to a certain taste.

Another thing we find hard to accept about Thaedra is that it's so heavy and gets so hot. You'd think that the heaviest and hot test preamp in our survey would be a vacuum tube unit. No, it's Thaedra. You can hardly lift it, and you can hardly touch it. We know there are good and sufficient technical reasons for this, but we prefer the sound of several preamps that have good and sufficient technical reasons for being light and cool. We must admit, on the other hand, that Thaedra is very solidly built, with a beautiful feel to the controls and an aura of quality throughout. It's also the only top-notch preamp we tested that has a headphone jack (not counting the power amp that comes with the Advent 300).

It must also be remembered that, since the head amp in Thaedra completely bypasses the signal path of the mag-phono preamp, testing it with a moving-coil cartridge is a whole new ball game. So it could either rise or drop in our ranking in Part II.

And the one last thing we said about the D B applies equally to Thaedra. If no better preamp existed, we could live with this one happily and never miss a thing, Not much.

Luxman C-1000

Lux Audio of America, Ltd., 200 Aerial Way, Syosset, NY 11791. Model C-1000 Control Center, $895. Three year warranty; manufacturer pays all freight. Tested #D6100162, owned by The Audio Critic.

As the flagship preamp of an exclusively high-end-oriented new Japanese line in America, this one is quite inadequate. For just under $900, you get a beautiful front panel with luxurious controls (they reminded us of a Mosler safe), a wooden furniture cabinet that clashes awkwardly with the technological feel of the front panel, no facilities for moving-coil cartridges (the design must be years old), and clean but undistinguished sound.

The C-1000 is pleasant to listen to, low in distortion, free from obvious sonic vices, but it takes only about two minutes of critical listening to relegate it to a distinctly lower category than, say, the ten best preamps in this survey. Its sound is insufficiently open; depth perspective is relatively poor; you could even argue that there's a wee bit of transistory aggressiveness to be heard from time to time; it Just isn't a thoroughbred. Switching from the Mark Levinson JC-2, for example, to the Luxman seems to lower the spatial ceiling of the sound to about half its height, and the JC-2 is far from the best preamp from that point of view.

It's too bad, especially since Lux Audio seems to be making a truly sincere effort to get on the right side of the American audiophile; what's more, they have already done so with their excellent PD-121 turntable (our reference).

Luxman CL-35/III

Lux Audio of America, Ltd., 200 Aerial Way, Syosset, NY 11791. Model CL-35/III Stereo Control Center, 8745. Three-year warranty; manufacturer pays all freight. Tested #F6101923, owned by The Audio Critic.

This is a vacuum-tube unit, and it came to us with a good grapevine reputation as a possible state-of-the-art contender. That it isn't, but it's a good preamp nonetheless; it wasn't really wiped out by any other in our survey, al though it can't survive A-B comparison with the best.

You could call the sound of the CL-35/III a typical tube sound (in the good sense): completely free from top-end hardness, beautifully dimensional and detailed in the midrange, a little plump in the bass (pleasingly but at the expense of accuracy), very good in depth perspective, though it isn't quite as open as we'd like it to be. It does have one rather subtle, elusive aberration that baffled us; there's a peculiar kink in the spatial image it presents- you could call it a buckle in the sonic canvas --so that the midrange seems to separate from and fold behind the higher frequencies from time to time. If this sounds confusing to you, it's because it does sound confusing when you hear it and is hard to describe. Since it's not unlike what we heard on the AGI 511, we're inclined to ascribe it to some kind of slew rate-related phenomenon.

The controls on the CL-35/111 are a joy, especially the excellent attenuator-type volume control with its click stops. The tone controls, too, are unusually flexible (rather similar to those on the C-1000, though not quite as elaborate); we amused ourselves by completely flattening out the RIAA equalization curve on the phono input with them. Try that on your preamp. Plug-in sockets for the Lux step-up transformers for moving-coil cartridges are also provided.

Everything considered, this is still not where it's at in tube preamps. If you can't kick the tube habit, what you need is the Paragon 12.

Luxman CL-350 Lux Audio of America, Ltd., 200 Aerial Way, Syosset, NY 11791. Model CL-350 Solid State Control Center,

$495. Three-year warranty, manufacturer pays all freight. Tested sample owned by The Audio Critic.

There's something depressing about the fact that the front panel of this unit is absolutely identical to that of the CL-35/III, except for the shape of two knobs. Since this is a solid-state preamp, that's a little bit like your choice of chocolate or vanilla in the same package. Matter of taste, sir. We sell 'em both.

To us the CL-350 doesn't taste as good as the tube version. The only reason why we included it in our survey was that a number of audio people whom we know and respect had started a ground swell for it as by far the best-sounding preamp in the Luxman line, despite its lower price, and one of the best preamps at any price. We disagree.

The CL-350 has a more open sound than the C-1000 but at the expense of introducing a touch of nastiness. Certain instruments take on a slightly nasal, ugly coloration through the CL-350. There's some hardness at all times.

It's not really a very listenable preamp, al though it's far from one of the out-and-out baddies in our survey. Nor is it nearly as musical in sonic texture as the CL-35/III.

We can't understand what our informants were talking about.

What we said about the control flexibility of the CL-35/III is of course equally applicable to the CL-350. Every position of every control is the same. But why can't any of these 15-knob jobs sound as good as the Advent?

Marantz 3600

Marantz Co., Inc., PO Box 99, Sun Valley, CA 91352. Model 3600 Stereo Control Console, $499.95. Three year warranty; manufacturer pays return freight. Tested #1118, owned by The Audio Critic.

Here's another preamp whose audiophile reputation seems totally inexplicable to us. One reviewer, not long ago, put it in the same class with Mark Levinson and Audio Re search. He must have been listening to it on some kind of AR box speaker with the tweeter control turned all the way down.

Saul Marantz, whose illustrious name this product carries (and sullies) although he hasn't had anything to do with the Marantz company for many years, could tell you what's wrong with the 3600. As a Dahlquist partner, his reference speakers are probably the same as ours, and the DQ-10's reveal grievous aggression by this preamp at the higher frequencies.

The needles it inserts in your ears aren't quite as excruciating as in the case of the BGW, which can lay claim to the longest and the sharpest, but the Marantz is a shoo-in for second place in this respect. Once you have to dive for the volume control for fast, fast relief, it becomes rather academic that the 3600 has beautiful, deep, tight bass, one of the best in the business. Or that it's quiet or even that it has all kinds of goodies on the front panel for extra flexibility. It just isn't listenable.

We must also add that the Superscope 3600 (sorry, Marantz 3600) was the only pre amp in our survey other than the Dayton Wright and the Paragon-both of which, unlike the Marantz, are products of tiny audio-freak companies-that came without even a single piece of paper or connecting hardware in the original factory-sealed carton. Our efforts to obtain a manual took several months of repeated long-distance and local telephoning.

When it finally arrived, the warranty page in it was stamped with a big VOID. Real communications.

Oh yes, you can also have this preamp with built-in Dolby B system, in which case it's called the 3800 and costs $100 more. Who cares.

Mark Levinson JC-2 Mark Levinson Audio Systems, 55 Circular Avenue, Hamden, CT 06514. JC-2 Preamplifier, $1050 (delivered with System A for magnetic cartridges). Plug-in System D for moving-coil cartridges, $175 extra. Tested #1924 A, owned by The Audio Critic.

This is generally spoken of as the Rolls Royce of preamps, a reputation difficult to live up to but essentially confirmed by our tests.

That doesn't mean it's the one preamp we'd want to own if we were allowed only one choice. But since it happens to be our good fortune that we can own more than one, we're going to hang on to this outstanding unit for a long time. In some respects, it's the best of the lot. (On the other hand, if you're looking for a Marantz 3600 in mint condition, we know where you can get one cheap.) Our initial purchase of a JC-2 for testing didn't go without a hitch, and in view of the rather holy self-image this company conveys to the audio community, the facts must be set down. First of all, the System D moving-coil boards we had ordered in addition to our basic System A unit didn't come packed with the latter. It took weeks before our dealer finally received them-mixed up with a repair order.

Also, the top cover of our JC-2 had some very strange nomenclature for inputs. It turned out to be the misplaced top cover of a Mark Levin son LNC-2 crossover (the size and the holes were identical-but where on earth was Phono 17). Finally, our unit just happened to fall into a recalled series (from #1855 to #1931), not unlike the typical Detroit recalls. It seems that the line driver modules in some of these 77 preamps were suspected of an audible but un measurable flaw, and Mark Levinson decided to replace them all. (We may be able to tell you in Part II of this survey whether or not the recall was a case of audio-hypochondria.) In the end, everything was fine and dandy; we got the correct top cover; we got the latest (and supposedly best) line driver modules; we had both System A and System D in perfect working order. What's more, our numerous tele phone contacts necessitated by these mix-ups had all been with unfailingly courteous, cooperative and intelligent people at MLAS. This company may not be as perfect as they'd like you to believe, but still-it's got class! When it comes to judging the sound of the JC-2 as critically as its renown and price tag demand, we must single out, before anything else, its magnificent highs. Nothing, repeat, nothing sounds cleaner, more neutral, more transparent, more delicate, more grainless in the high-frequency range than the latest JC-2.

We're even tempted to say, not even a straight wire, but we haven't so far gotten around to a suitable bypass test that works through a phono stage. The bass is almost equally impressive: tight, detailed, with tremendous impact on transients, but without the slightest heaviness.

In between, the midrange is a little more arguable (more about that in a moment), but its clarity cannot be denied. What ultimately had us sold on the JC-2, though, is its behavior when passing really brutal transient. It just never lets go; everything comes out as tight, as together as it went in. There's no softening of orchestral sforzandi nor of the attack transients of the piano. At the same time, there's absolutely no hardening of the sound under these stressful signal conditions, either. In the reproduction of sonic texture, there's really no preamplifier we know of that surpasses the JC-2 in accuracy.

Spaciousness and depth perspective, particularly in the midrange, are another matter.

On our reference system, with the Quatre DG-250 power amplifiers (slew rate 40 V/uS), the JC-2 is strikingly inferior to the Rappaport PRE-1 and the Audio Research SP-4 in resolving spatial information. The sound stage be comes smaller in all three dimensions, but especially in depth, when you switch from either of these preamps to the JC-2. It's through the Yamaha B-2 (slew rate 60 V/uS, the highest in our collection) that the JC-2 comes into its own. Through this power amp, which we rate below the Quatre because of a slightly brittle top end, the JC-2 sounded indisputably more beautiful than any other preamp in our test, including the Rappaport.

(But we had no opportunity to test the SP-4 through the Yamaha before press time.) This was a truly synergistic combination, eliminating most of the high-frequency hardness of the Yamaha as well as the depth-imaging problems of the JC-2. A quick telephone call to John Curl, the consulting engineer who designed the original JC-2 circuit (hence the model designation), brought forth the information that the JC-2, with its superfast high-level stage (over 100 V/uS), is happiest with a very fast-slewing power amp. (Cf. the Rappaport letter.) With all other power amplifiers, how ever, we preferred the Rappaport, as it sounded considerably more like live music in its rendering of spatial detail, while sharing most of the virtues of the JC-2 (except possibly the ultimate in top-end smoothness).

A quick check of the System D version of the Mark Levinson, with the Denon DL-103 cartridge, left its relative ranking unchanged with respect to other preamps that accept moving-coil cartridges. Details will be forth coming in Part II of this survey.

In view of its stratospheric price, some comments on the JC-2's construction details are in order. The basic concept of an ultra-flat, ultralight unit appeals to us. For one thing, it's less likely to get banged up when moved around. (Like an attaché case vs. a suitcase.) Whether the quality of circuit components, switches, pots, etc., justifies the price is hard to judge. We haven't seen anything better; on the other hand, some other very beautifully made units cost a hell of a lot less. We have a feeling that (a) Mark Levinson has made the price part of the JC-2's elitist appeal and (b) Mark Levinson's profit margin (strictly on the hardware) is higher than, say, Audio Re search's. We'll never know for sure.

It could even be argued that the high quality construction of the JC-2 has an artsy craftsy rather than technological thrust. When you take off the top cover, you see an almost amateurish tangle of wire between the controls and the circuit boards. It makes a kit builder feel right at home. This is not the way Hewlett-Packard makes an expensive piece of electronic gear. On the other hand, the Teflon wire is the best money can buy. Every thing in there is the best money can buy. Like a wealthy gourmet's home pantry or an executive's Sunday paint-box.

Incidentally, those interchangeable plug in circuit boards drove us right up the wall.

To extricate the D system, for example, and insert the A system requires the patience of Job and the skill of an eye surgeon. We used a fiberglass TV alignment tool that was strong enough to pry with but not hard enough to chip anything; even so we ended up with bent prongs.

(They can be straightened out; like everything else on the JC-2, they're well made.) Suddenly we understood. The Mark Levinson JC-2 isn't the Rolls Royce of preamplifiers. It's the Lamborghini Countach. Its eccentricity and its quality are part and parcel of the same quirky, single-minded concept.

Editor's Note: At press time we hear that the JC-2 has acquired a new power supply, a new power supply filter module, and new super deluxe jacks that don't mate with standard RCA-type plugs. What's more, its price is going up by several hundred dollars. The more you sock it to those Lamborghini types, the more they love it, eh Mark?

Paragon Model 12

Paragon Audio, 997 East San Carlos Avenue, San Carlos, CA 94070. Model 12 Preamplifier, $850. No warranty information enclosed with original factory container. Tested #7609182, owned by The Audio Critic.

What we said about the GAS Thaedra is possibly even more applicable to the Paragon: to some audio enthusiasts this will be the world's best preamp, and nothing will change their minds. We must confess that we, too, were instantly seduced by the sound of the Paragon; however, it turned out to be a seduction that wasn't followed by marriage in due course.

The Paragon Model 12 (we aren't talking about the older Model 10, mind you) is a vacuum- tube preamplifier that offers you the fabulous midrange of the Audio Research SP-3A-1 (or at least a midrange within a hairs breadth of that all-time standard) without any of the SP-3A-1I's glary, irritating upper frequencies-in fact, the highs are beautiful and very detailed-and adds to it all a tremendous, authoritative spaciousness, especially front-to back depth, plus a kind of Technicolor gorgeousness of timbre. It's irresistible; we love it and will hang on to our unit for further testing; but we really don't think that this is the sound of "a straight wire with gain." It isn't 100% accurate. We could still turn out to be wrong; a number of respectable golden ears disagree with us; but we must call them as we hear them. Besides, no one who listened to the Paragon at length on our reference system is among the dissenters.

With some combination of components the slight colorations introduced by the Paragon are easily identifiable. For example, with the GAS Son of Ampzilla driving the Dahlquist DQ-10's, the Paragon has a fat upper bass and lower midrange. Even with the Yamaha B-2, which appears to be more compatible with it, it tends to soften piano transients and wipes a little bit of rosin off the bows of a string quartet. In other words, it's still a tube preamplifier-although the best we've ever heard.

Mark Deneen, the Paragon's obviously very knowledgeable designer, told us that he believes tubes are vastly superior to other amplification devices, even at low signal levels, and that the next, still more sophisticated pre amp he is working on is also a vacuum-tube unit. He also believes in very high slew rates (we found that the Model 12 clips at 38 volts peak-to-peak at 50 kHz!), very extended high frequency response, and no RF filtering. He is convinced that the presence of any kind of RF filter circuit is audible in the audio range.

As a result, the Paragon 12 is hyper sensitive to RFI (radio frequency interference); if there's intensive CB activity in your immediate area, the Paragon will be simply unlistenable. (It happened to us for a solid week;

then the ten-four-old-buddies suddenly pulled out of our neighborhood and there were no further problems.) We understand that Paragon Audio has been extremely cooperative in finding individual solutions to this problem for various customers.

Our recommendation, then, regarding the Paragon is: listen to it. Especially if you've always been a tube freak. But don't just listen for five minutes because then you'll surely buy it, and it isn't cheap.

----------------------

Say Bongiorno to Servicing Hassles

As you can see elsewhere in this report, we consider the GAS Thaedra to be a truly fine pre amplifier. We even respect the opinion of those who believe it's the best-sounding preamp there is, although we aren't willing to go quite that far. But it was the only unit that conked out on us in the course of these tests, and the experience we had trying to get it repaired at the factory is something our subscribers ought to know about.

We were well along in our laboratory and listening tests of Thaedra #500790 when we gave it an ever-so-slight jostle while making some connections. It was just the teeniest tap of the elbow, really nothing, and the unit didn't even budge an eighth of an inch. But a few seconds later it emitted a most alarming cough and several minutes later its gain dropped to virtually zero, from input to output. And we mean all inputs, all outputs, both channels, any control position. We later found out that the relay circuit is occasionally sensitive to such up sets, but in any event the unit obviously needed more than routine servicing.

Since the dealer who had sold us our Thaedra is located about a fifty-mile round trip from our area (and a lot of it suburban shopping center driving), we decided to contact the factory directly. Not as The Audio Critic (hardly anyone knew about us at the time) but just as the average Joe Customer. We now wish we had gone back to the dealer, who later assured us that he would have handled the whole affair, logistically and financially, without involving us in any way.

We called up the factory, long distance, and were told by some body named Vince that if we air freighted the Thaedra to them they would keep it only three working days, repair it and test it, and air freight it right back. The day we figured they must have received it, we gave them another ring, just to make sure. Vince informed us that they had indeed received it but, if we wanted it back, we must send a certified check or money order for the return airfreight: $15.86.

We said, wait a minute, the only time we had ever been asked to bring a certified check was when we picked up a $6000 car. It was bad enough that the company didn't pay return freight on the repair of a brand new unit, but to assume that someone who had paid $909 for a preamplifier might be passing bad fifteen-dollar checks-really! Vince said sorry, that's the way it is.

By the sheerest coincidence, we met Jim Bongiorno, the scrappy little president of the GAS company, that very evening. He had come east to demonstrate his new Ampzilla II, and the dealer in whose showroom the demonstration took place introduced us to him, still not as The Audio Critic but as a good customer. We complained to him about the certified-check nonsense, but he remained very hard-nosed and asserted that it was the only way GAS could do business because they were holding a lot of small checks that had bounced, including return-freight COD's. We said, look, this is one of your trusted dealers; he knows us and will vouch that our check is good. Just save us the trouble of running to the bank or the post office. Sorry, he said, it wasn't his department, anyway. Our final re mark was that GAS seemed to be trading in some very small losses against a lot of bad will with this insulting policy. "I'll take the bad will," he said.

We realized that the man obviously believes that you just have to go to GAS if you want the best equipment, whether you're pleased with their policies or not. We had no choice, so we sent them a postal money order the very next morning.

Then-nothing. No Thaedra for a week. No Thaedra for two weeks.

During this period we spoke to Vince at the factory several times.

The first time, we found out that they hadn't touched our unit for a solid week after its arrival. Some urgent export business had to be taken care of first, we were told.

(So the airfreight had been a waste of money.) Then we were told the unit had left the plant and was on its way. It wasn't. When it finally arrived, three weeks had elapsed from the day of the original failure, despite our instant action and two way airfreight.

But that, of course, wouldn't be cause for this kind of report.

Now get this: When we put the Thaedra back into our system, we discovered that the five-position mode switch was completely busted. It wouldn't even go into its first two positions and could be twisted about ninety degrees past its last position, where it hummed like a vacuum cleaner. It had been perfect when we returned the unit, but we figured one of the large anthropoid apes shown in the GAS ads must have twisted it in the service shop be cause no H. sapiens in the audio business would have been capable of that kind of brutality.

Somehow we managed to find the stereo mode, regardless of what the knob was pointing at, and started to do some listening. The denouement came a few minutes later. Our Thaedra went out of commission with exactly the same defect that had made us return it in the first place. No gain. Hardly any output.

Obviously it hadn't been repaired.

Back to square one after three weeks.

Needless to say, we were on the phone with Bongiorno almost immediately. And this time he was all sweetness and light. Whether he had found out meanwhile that we were The Audio Critic (he didn't say so) or is merely a man of many moods, we'll never know. But he said he wanted happy customers, not un happy ones, and he would immediately arrange for the exchange of our defective unit against a brand new one through the original dealer.

That, of course, took the wind out of our indignant sail, and we actually thanked him for the fairness of his offer.

The trouble was that our dealer had no new Thaedras in stock and the factory couldn't deliver any for another two weeks. Lots of finished units, we were told, but they were all lacking knobs. (Those anthropoids again?) We could have our unit when the knobs came in.

By the time we finally had our beautifully working and really excellent new Thaedra #500961, we had been without a usable one for well over five weeks. And we were out about fifty bucks for airfreight and long-distance calls, which we weren't reimbursed for. Luckily we had started testing the Thaedra fairly early, and we had at least 18 other preamps on hand during those weeks.

But what about the average customer? Especially if he doesn't live near a dealer? We aren't suggesting that this is what will happen to you if you buy a Thaedra. Nor that the same couldn't possibly happen to you if you deal with any other company.

(Although other audiophile companies like Audio General and Rappaport will pay two-way freight on bona fide warranty repairs, and still others like DB Systems will pay at least return freight.) But this is precisely what happened to us, and the company happened to be GAS. You can draw your own conclusions.

We'll even admit that it's a stroke of bad luck for a company when the customer to whom this sort of thing happens is in a position to publish the story. But that's the way it is, Jim and Vince. Never give a masked stranger a hard time because he could turn out to be the Lone Ranger.

-------------------------

-------------------------

Are Openness and Depth Simply a Matter of Low TIM?

Editor's Note: We were so taken with the sound of the Rappaport PRE-1 that we decided to ask Andy Rappaport, its phenomenally young and articulate designer, whether it incorporated a special circuit philosophy. His reply was interesting enough to be reproduced here in its entirety.

To the Editor:

The key to the sonic performance of the PRE-1 is a design that minimizes the effects of time delay distortion. Careful study of the causes and effects of varying the subtle time elements of recorded music has enabled me to develop de sign criteria for components which, I feel, accurately reproduce depth and openness, and also perform well on all of the standard laboratory tests.

When the ear perceives depth, it relies very heavily on time delay information. Because the speed of sound in air is a constant (for any given ambient temperature), the greater the distance is between a source and a sensor, the longer it will take for a sound to travel from one to the other. Thus, if two sources that are at different distances from a sensor emit sounds simultaneously, they will be perceived as two distinct sounds, separated by a delay proportional to the distance between sources.

It is this phenomenon that the ear uses in registering depth. Therefore, it is important that this time delay information be retained and properly processed by an audio system intended to reproduce a ''depth image." One factor that causes the deterioration of such an image is Transient Intermodulation Distortion (TIM). This is introduced in amplifiers with high open loop gains, employing large amounts of negative feedback. An overshoot is produced, in such amplifiers, during the time when an input signal is present with no output to be fed back. (This period is the forward propagation delay of the amplifier circuit.) An overshoot of sufficient amplitude will often exceed the overload ceiling of the input stages, and the signal will be "clipped." If a square wave is introduced at the input of an amplifier exhibiting much TIM, an overshoot 'will result for each leading edge. If this square wave is stepping a sine wave, the overshoot will cause a small segment of the sine function to disappear. Furthermore, if the sine wave is modulated by two square waves, slightly out of phase, it would disappear between the two leading edges, causing the two square waves to appear as one (approximately). If the two waves represent sounds emitted simultaneously by two musical instruments, and the phase angle between them is proportional to the distance between the sources, the little piece of sine wave which has disappeared is important in retaining the depth information. When it is lost, so is the depth image.

The PRE-1 was designed to minimize TIM. The open loop gain of the phono stage approximates the RIAA equalization curve, so that when the small amount of feedback is applied it is a constant for all frequencies.

(Most phono preamps have extended open loop bandwidths, which result in increased feedback at high frequencies, in order to reduce the gain in accordance with the equalization curve.) Because the open loop gain at high frequencies is low, the over load ceiling is quite high. Thus, even the open loop amplifier is impervious to overload by the output signals of standard phono cartridges. In addition, overshoot is reduced by a very small propagation delay and lack of phase shift in the audio range.

Another unique feature of the PRE-1, intended to minimize time delay distortion, is that it is slow.

The slew rate of the phono stage is a mere one volt per microsecond (as compared to 20V/uS for the Mark Levinson JC-2), and the high level stage will slew at no more than 20V/uS (as against more than 100 V/uS for the JC-2). I am told that in slowing down my preamp, I am being technically backwards, but my reasoning is simple:

If an amplifier with a gain of twenty decibels sees an input that changes fifty volts in one microsecond, its output would have to change five hundred volts in the same microsecond.

If it is incapable of such a slew rate, the signal would become severely distorted. (Consider the example used above, of two out-of-phase square waves and a sine function. If the two square waves rise too fast, they would appear as one, resulting in time delay distortion.) Thus, the slew rate of any stage in a chain of amplifiers must be no less than the product of its gain, times the slew rate of the preceding stage. Remembering that power amplifiers are usually quite slow (the fastest power amplifiers that I know of, which are listenable in all other respects, slew at a little more than 40V /uS) and have high voltage gains, the faster the preamp, the worse the depth imaging.

The slew rate of the phono stage of the PRE-1 is the minimum value for such a stage (its bandwidth is limited to a little more than twenty kilohertz at five volts rms) and the high-level stage was designed to be slightly faster than required to allow for optimum performance with sources that are slightly faster than the phono stage. Of course this is a bit fast for perfect results when used with currency available power amplifiers, but if the preamp were any slower, its high frequency distortion would be too high.

The solution, of course, is to develop a faster power amplifier.

I find that the PRE-1 works best with amplifiers combining fast slew rate with relatively low voltage gain (i.e., low power and low sensitivity). To obtain higher power levels, two fast, low-power units should be used in a monaural mode (one channel inverted). This way, increasing the power also increases the slew rate, as in mono, an amplifier with a 40V /uS slew rate will slew 40V /uS positive in one channel, while the other channel goes negative at the same rate, resulting in an effective slew rate of 80V /uS.

I hope that I have shed some light on a complicated subject. Should you have any further questions, please contact me, as 1 would be happy to discuss them with you. I am currently preparing an engineering paper which discusses these ideas in a somewhat more technical and involved manner, and I hope to make it available shortly.

Thank you for your interest, Andrew S. Rappaport President A.S. Rappaport Co., Inc.

-------------------------

Quad 33

Acoustical Manufacturing Co. Ltd., Huntingdon, Cambs. PEI8 7DB, England. Quad 33 Control Unit, 8265. One-year warranty; customer pays all freight.

Tested #62675, owned by The Audio Critic.

Nothing with the Quad label on it has ever been a negligible product from the audio purist's point of view, which is why this preamp is in our survey, even though its price is in the

"popular" category. Besides, its physical construction, finish and production details are of a caliber seldom seen in equipment at twice or even three times the price.

If it weren't for the new Advent 300, the Quad 33 would also be the greatest sonic bar gain discovered in our survey. This is no $265 sound. It's unfailingly clean, sweet, musical, and nonirritating. Typical units in the $450 to $500 range, such as the Marantz 3600 or the Epicure, don't even come close. But the Advent, for $5.05 less, wipes out the Quad. The latter has a somewhat puffy fatness and slight loose ness to its upper bass and lower midrange, as well as a lack of truly extended and detailed highs, that put it in a distinctly lower category.

On the other hand, the Quad 33 has the most sophisticated and useful high filter in the business. The variable corner frequency and variable roll-off slope allows you to filter out exactly as much garbage as necessary, no more and no less, without throwing out the music with it. No other preamp at any price has any thing comparable.

It must also be remembered that, since the Quad 33 is designed to work with the high gain Quad 303 and Quad 405 power amps, it doesn't mate too well with typical American and Japanese amplifiers having higher input requirements. With the 405, especially, it comes into its own, and the two together form quite an impressive $675 package.

The grapevine has it that Quad may soon be out with a new preamp, which should be very interesting if it beats the 33 by as much as the 405 did the older 303 in power amps.

Rappaport PRE-1

A. S. Rappaport Co., Inc., Box 52, 146 Bedford Road, Armonk, NY 10504. Model PRE-1 Stereo Preamplifier, 8575. Three-year warranty; manufacturer pays two-way freight. Tested #1022, owned by The Audio Critic.

Rappa who? This one got into our survey by the merest chance, as we had never heard of it. Luckily, one of our trusted consultants had, and we were on our way to our most rewarding discovery thus far in the labyrinthine byways of the audio industry. Right now, as we report this, the preamplifier in our reference system is the Rappaport PRE-I.

The story of this new product is very American. A young Princeton student by the name of Andy Rappaport decided that the way they were teaching him electronics in class would never lead him to bigger and better things in audio design, which was his consuming passion. So he quit college and started to manufacture his own highly unorthodox pre amp design. For a kid who didn't know what he was doing, it would have been a pretty flaky thing to do. We have met Andy, have quizzed him about his theories (we ended up with a long letter from him, which we're reproducing here), and have concluded that it was a smart and gutsy thing to do. The preamp is now beginning to make waves in avant-garde audio circles.

Just to look at, the Rappaport PRE-1 isn't particularly awe-inspiring; it's a cute little black box, not very much bigger than the D B mini-preamp, even though its power supply is self-contained and a full complement of controls (including bass, treble, high and low filters, tape 1/tape 2 monitor, etc.) is included.

(This shoehorning, as we shall see, is actually the cause of the one minor flaw of the PRE-1.) We rather like its understated look, but it's no techno-turn-on for sure.

Since the circuit philosophy is completely explained in the letter from its designer, we'll go straight to the sound of the PRE-1. It's thoroughly clean and tight. Bass impact is tremendous, without a trace of heaviness or hangover; the midrange is extremely vivid, almost palpable; the highs are for once properly and realistically embedded in the overall sonic fabric instead of jumping out at you.

Spatial relationships, especially front-to-back depth but also width and height, are reproduced with unprecedented accuracy; you could say that what the Audio Research SP-3A-1 does for midrange perspective 100%, the Rappaport does for the entire audio range about 98%. The highs of the PRE-1 aren't quite as astonishingly pure and delicate as the Mark Levinson JC-2s, but they're accurate and non-fatiguing. On our reference system, through the Quatre DG-250, the Rappaport was clearly the preference of our entire staff over the Levinson; through the Yamaha B-2 the reverse was the case, the JC-2 sounding even cleaner and smoother overall, as well as more nearly perfect on transients.

(We refer you to our Mark Levinson review for full details.) Through the GAS Son of Ampzilla, the Rappaport was again our top choice; it just seems to beat the JC-2 on more systems than not, mainly on account of its superior reproduction of depth and other spatial information. These two units are both quite exceptional, and in view of their totally different techno-personalities (the Rappaport is essentially very well made but doesn't make a religion of component quality) the choice is ultimately up to the individual audio enthusiast on the basis of his own priorities.

The price ratio is about 2 to 1.

Editor's Note: In the end, the new Audio Research SP-4 proved to be the toughest com petition for the Rappaport, but it survived that challenge, too. (See the SP-4 review above.) Is there anything wrong with the Rappaport? Of course. For one thing, it hums. Not that you'll ever hear the hum under ordinary operating conditions. At normal playing levels it will be far enough below the signal level to be unnoticeable, although we measured considerably worse hum in the right channel than there should have been according to the spec sheet. (The left channel was comparable to the JC-2!) The main hum problem is under the rather irrelevant condition of no signal output, with the volume control turned all the way down. In a carpeted room with low ambient noise, the hum will then be audible, especially through efficient speakers connected to a fairly high-gain power amplifier (e.g., Quad 405 or Yamaha B-2).

The reason for this small boo-boo is that the transformer is too close to the signal carrying leads in that tight little box. Two fixes are possible. One is to connect a 10K resistor between Main Out 1 and Main Out 2 and an other 10K resistor between Main Out 2 and ground. Do this on both channels and use only Main Out 2. This acts as a voltage divider circuit that knocks the hum level down another 6 dB under the no-output condition.

That should make it inaudible, at the expense of a 6 dB decrease in gain (no problem) and an increase in output impedance (could be a problem but not likely). The better solution, if you're a purist, is to wait until February, when the PRE-1A chassis ($515) with separate PS-1 power supply ($200) will become available.

(In other words, the D B and Mark Levinson route.) If you don't feel like spending the extra $140, all we can tell you is that in a typical installation the hum problem doesn't seem to be an issue. (A Rappaport head amp is also coming in February.) Speaking of purists, don't worry about the tone controls on the Rappaport. They can be completely bypassed with the flick of a switch, and even when you switch them in the difference is barely (and we mean just barely) audible in their centered position. This is a sophisticated design.

If the PRE-1 were, say, a new McIntosh preamp, we'd call it a remarkable achievement. For the first product of a very young man and a very small company, it's a tour de force.

Stax SRA-12S

American Audioport, Inc., 909 University, Columbia, MO 65201. SRA-12S Integrated Amplifier for Ear Speaker, 8500. No warranty information enclosed with original factory container. Tested #E1210, owned by The Audio Critic.

The ads for this preamp state that "it doesn't have enough knobs to look at" but that "it sounds better than preamps costing up to twice as much, so some dealers are afraid of it." Aha, we thought, they feel it puts the GAS Thaedra or even the Mark Levinson JC-2 to shame; this we've got to test. We did and our finding was: no way. The sound of the SRA-12S is definitely flawed.

This unit is actually more than just a pre amp; it includes a main amplifier stage with a gain of 60 dB, specifically designed to drive the Stax electrostatic headphones. We didn't test it in that application (although we intend to when we do a comparative review of headphones); we're only reporting here what it does at "pre out." The preamplifier section itself it set up in such a way that you can use the phono stage (gain: 40 dB) all by itself to go directly into your power amp or, if that amount of gain is insufficient (it usually is), you can switch in the high-level stage, which Stax calls the inter stage amplifier (gain: 20 dB). Since we don't really like the sound of the Stax either way, we don't feel that a highly analytical discussion of the slight sonic differences between these two models would be productive. We listened mainly with the [.S. amplifier switched in; we just didn't have enough gain for our reference cartridge through the phono stage alone. (With a pre-preamp or transformer, you don't need

the I.S. preamplifier; or, alternately, you could plug the moving-coil cartridge directly into the preamp and in most cases have sufficient gain when the [.S. amplifier is switched in.) On program material without a wide dynamic range and concentrated mainly in the mid-frequencies, the Stax sounds like a first rate preamp, airy and well-defined. But let somebody hit a suspended cymbal or tinkle a triangle, and you'll think your telephone is ringing. Some people we know call this fizzy, ringing reproduction of the high frequencies

"the Japanese sound; that seems like an overly glib generalization to us, but we have heard it on a number of Japanese units. (The Yamaha C-2 is the most egregious example.) Others attribute this type of sound to FET's (the Stax is an all-FET design, but so is the Yamaha C-1, which sounds smooth as silk); we have no opinion on the subject at this stage of our investigations. In general, when the music gets complex and dynamic, the sound of the Stax SRA-12S hardens audibly.

Our recommendation: get a D B for $75 less or an Advent for $240.05 less. And if you're the last of the big-time spenders, get a Rappaport for $75 more.

Yamaha C-1

Yamaha International Corp., PO Box 6600, Buena Park, CA 90620. NS Series C-1 Stereo Control-Amplifier, 81800. No warranty information enclosed with original factory container. Tested #1951, owned by The Audio Critic.

On the basis of its overwhelming visual and tactile presentation, its unique Star Trek techno-gestalt, its staggering price tag-this has got to be It. The world's greatest preamp.

Thirty-one (count them, 31) knobs and switches up front, many more in the back, a pair of magnificent peak-reading meters, LEDs lighting up all over the place, a built-in test oscillator and pink-noise generator-shall we go on? Beam us aboard, Scotty; give us a reading, Mr. Spock.

Too bad the sound is no match for a $260 Advent, let alone the top two or three preamps in our survey.

Not that the C-1 sounds bad. Yamaha couldn't get away with that. It sounds smooth, so smooth that in the early phases of our survey we called it the homogenized-milk preamp. Distortion is extremely low; long-term listening is non-fatiguing. If you never compared the C-1 to anything else, you could easily persist in the belief that you got your $1800 worth. It so happens, though, that the D B was the very next preamp delivered to us after the C-1, and there was just no comparison. The C-1 was wiped out. It simply can't deliver the completely free, open, spatially and texturally detailed, highly dimensional sound of today's top preamps. Overall, we'd rank it maybe 11th or 12th among the 22 units we tested, no higher.

Switching back to the C-1 from something like the Rappaport makes an audible ceiling descend on the sound stage, as if lowered by pulleys. That you-are-there openness just vanishes.

Another serious shortcoming of the C-1, despite its formidable battery of features and facilities, is the complete absence of pro visions for moving-coil cartridges. Just as though they didn't exist. After you've paid

$1800, it's still your problem how you're going to bring up the level of your moving-coil cartridge to the 2-millivolt input sensitivity of the C-1. (It's possible that the design was finalized before the current popularity of moving-coil cartridges took hold.) By the way, that built-in oscillator with four test frequencies (70 Hz, 333 Hz, 1 kHz and 10 kHz) is strictly a promotional gimmick. So is the pink-noise generator. Look at it this way.

A Krohn-Hite 4100A push-button oscillator (0.01 Hz to 1 MHz, about 0.005% average distortion in the audio range) costs $695. A General Radio 1382 white/pink noise generator costs $675. A DB Systems preamp costs $425.

Total: $1795. So, for $5 less than the price of the Yamaha C-1, you can get two superb professional lab instruments plus a better preamp. And the Krohn-Hite alone has 40 controls on its front panel, nine more than the C-1, if that's what your heart desires.

Our overall judgment of the Yamaha C-1 is that it's probably the ideal prestige preamp for the successful young Wall Street man who, between the stock market, the tennis club and the Ferrari Daytona, has no time left for the concert hall. But for those who are regularly exposed to the sound of live music, there are more satisfying preamps at less than one third the price.

Yamaha C-2

Yamaha International Corp., PO Box 6600, Buena Park, CA 90620. NS Series C-2 Stereo Preamplifier, $650. No warranty information enclosed with original factory container. Tested #02147, owned by The Audio Critic.

Since the Yamaha B-2 power amplifier is an exceptionally fine piece of equipment (more about that in our second issue), we were really disappointed that the companion preamplifier that's supposed to go with it, the C-2, isn't nearly up to the same sonic standard. Here was Yamaha's chance to do everything right the second time around-and they muffed it.

The Yamaha C-2 is obviously a bid for the role of a poor man's Mark Levinson; it has the same flat, black styling, very sexy, but much, much heavier on account of the self contained power supply, full complement of controls, and built-in moving-coil pre-preamp.

Beautifully finished, too; the top and the front, for example, are a single extrusion; no small American audio-freak company could afford this kind of production engineering. It would all be a marvelous package for $650 if it weren't for the sound.

When you first turn on the C-2, the Mark-Levinson-esque impression is confirmed, since the noise level of the unit is absolutely the lowest in the business (fantastic!) and the sound is beautifully open and detailed. You say to yourself, "Hey, they did it!"-and then, kshhhh, there comes the 'Japanese sound" on the high-frequency transients. In the case of the C-2 this is even more pronounced than on the Stax: here the tinkling of the triangle is with out exaggeration like the ringing of your tele phone (somebody please pick that up, I'm listening to music). Cymbals, attack transients in the highest reaches of the violins, snare drums, castanets-everything way up there is falsified. If it hadn't been for this one disastrous flaw, we would have needed a runoff A-B test of the C-2 against our top choices; it's that good otherwise.

The most remarkable part of all this is that a slight brittleness or over-brightness is the B-2 power amp's only vice, so that the C-2's flawed high frequencies are even further exaggerated through it. This is compatibility? The Mark Levinson JC-2, for example, mates much better with the B-2.

Here again, we may be into a slew-rate interfacing situation. We'll look into that question more deeply as our test program evolves.

Yamaha CA-1000

Yamaha International Corp., PO Box 6600, Buena Park, CA 90620. NS Series CA-1000 Stereo Pre-Main Amplifier, $600. No warranty information enclosed with original factory container. Tested #22066, owned by The Audio Critic.

Here's the ultimate paradox in the Yamaha line: for $50 less than the C-2, they offer you an integrated 75-watts-per-channel stereo amplifier, in which the preamplifier can be used separately (as in the Advent 300) and sounds better, in some ways, than either the C-1 or the C-2. You even get a built-in moving-coil pre-preamp.

Again, we didn't test the power amp section, since for the purposes of this survey we were interested only in the preamp, which we had decided to test in view of its underground reputation for surprising quality. The rumors turned out to be reasonably close to fact; the preamp section of the CA-1000 sounds more open than the C-1 and is more listenable on the top end than the C-2. If it lacks the vices of its stable-mates, it doesn't quite share their virtues: it doesn't sound as smooth as the C-1 nor as open as the C-2. And it isn't quite free of that slight transistory hardness characteristic of nearly all commercial solid-state equipment, the sound that says "electronics" even when it produces no major irritation. The closest thing to this type of sound in our survey was the Luxman CL-350; if anything, the Yamaha CA-1000 is a little better.

If we sound a tiny bit bored with this one, it's because neither its pluses nor its minuses are very interesting to the audio purist. There's very little reason to get involved in this piece of equipment; the Advent 300 is better, as a preamp, at less than half the price, and there are about a half dozen other preamps in this survey that beat the CA-1000 on both sound and price.

On the other hand, if you're looking for a pretty good preamp along with a pretty good medium-powered amplifier at a pretty good price, the CA-1000 is hard to beat.

But pretty good isn't the name of the game we're playing here, is it? Recommendations With the reminder, once more, that all of the above is work-in-progress and that our conclusions may change as this survey goes into its second part, here are our present recommendations to those who wish to buy a pre amplifier immediately.

Best sound through mag phono, regard less of all other considerations: Rappaport PRE-1 (with the caveat about hum-see review).

Alternate choice for better system compatibility in specific cases: Mark Levinson JC-2.

Close to the best at a much lower price: Advent Model 300.

-----

[adapted from TAC, Vol.1, No.1 ]

---------

Also see:

Box 392: Letters to the Editor

Various audio and high-fidelity magazines