Preamps Without End (They Still Keep Coming) (Vol.1, No.6: Spring-Fall 1978)

Nothing in audio changes faster than the preamp scene. Here we go again: the latest developments, some interesting add-ons and plug-ins, and completely new top choices.

Before you get too deeply into this, we must ask you to read our introduction to the power amplifier reviews in this same issue, since preamps resemble quite closely the low-level stages of power amps and impose the same frustrating limitations on sonically correlatable laboratory measurements. It would be repetitious for us to make the same observations here about our second thoughts on the subject and about our current procedures, so please refer back to the other article.

That old villain, the RIAA curve.

One thing that makes preamps different from power amps, though, is that the first stage of a preamp must handle a pre-equalized input signal. The sharply boosted high frequencies of the RIAA recording characteristic have been the downfall of many a preamp design. When those high velocities are accurately traced by the stylus and transmitted to the preamp input more or less intact (as they appear to be by our extraordinarily "fast" reference cartridge, the Fidelity Research FR-1 Mk 3F, through the Cotter transformer), that first stage just goes "crunch" in some very highly respected preamps.

The truth is that the RIAA preemphasis curve should never have been standardized in its present form; the 6-dB-per-octave high frequency boost should have been stopped with a shelf at, say, 7 kHz. That's not a very hopeful cause for a reformist after 25 years; on the other hand, the utterly wrongheaded new IEC Recommendation (to roll off the RIAA playback curve 6 dB per octave on the bottom end, with the -3 dB inflection point at 20 Hz) may still be resisted before it becomes an RIAA Standard. We editorialized at some length on this in the last issue and are glad to observe that most preamp designers have thus far been ignoring the whole silly business. Unfortunately, they've also been ignoring our remarks about the wrong topology in RIAA equalization net works; too many preamps show the typical saddle-and-hump error curve that results.

Stanley P. Lipshitz of the University of Waterloo ( Ontario, Canada) recently struck a resounding blow on behalf of accurate RIAA equalization with an outstanding Audio Engineering Society paper that analyzes the subject in depth and fully corroborates our inevitably less authoritative journalistic carping.

Measuring the RIAA equalization error is of course one respect in which our laboratory tests on preamps differ from those on power amps, and the data obtained are generally more revealing than most. We consider a measured error of +0.2 dB to be tantamount to perfect equalization; +0.5 dB begins to verge on audibility; in between we're not so sure. We must hasten to add that amplitude response errors never sound as unnatural as high frequency cross-modulation effects, which are probably the most common form of audible preamp distortion but very hard to catch on the wing.

Tubes vs. transistors.

Since two of the best preamps we've come across lately are vacuum-tube units, we want to make sure that the prevailing irrational cultisms on the subject don't rub off on us by implication. We don't believe that electrons have any memory of the type of device they've passed through. The waveform of an audio signal is either altered or not as it passes from input to output through a circuit. We hear the alterations, if any, not the nature of the circuit components. An unstinting application of either vacuum-tube or solid-state technology will preserve the waveform with the same accuracy, provided that the circuit designer doesn't lapse into conventional errors. There's the rub.

"Tube sound" and "transistor sound" should be reworded as "sound due to typical tube-circuit design errors' and '"'sound due to typical transistor-circuit design errors." That doesn't mean, of course, that the choice between the two is six of one and half a dozen of the other. The vacuum tube is a natural audio amplification device; the transistor must be manipulated. An untutored tube-circuit designer is therefore more likely to get good re sults than an equally untutored transistor circuit designer. On the other hand, tubes are not nearly as stable and reliable in the long run as solid-state devices, so that the more complex manipulations to make the latter behave are mandatory for the future of audio and already successful in the present state of the art, though not much below that level.

Okay? Are we still nondenominational?

The listening tests.

The preamplifiers under test were inserted into our "Reference A' system (see article in this issue) and compared two at a time with the gain on all channels set equal within 0.25 dB when playing the 1 kHz reference tone on a standard test record.

With the accurate tracing of fast transients by the reference pickup, no low-frequency garbage fed back by the reference turntable, plus the high resolution of this unsmeared information by the reference speaker, the differences heard from preamp to preamp were quite startling. Genuine cleanliness of sound was the exception rather than the rule; a slightly but perceptibly raunchy quality was added even by our previous top choices; and we began to realize that, when reviewers prefer the "liquid" highs of this one but not its "hooded" mid range and the front-to-back *'depth' of that one but not its "warm" upper bass, they're talking about their personal taste in the distribution of sonic crud, without having a clean reference.

Clean is clean and there's no mistake about it; it just happens to be rare and expensive-and never so absolutely clean that something cleaner won't come along eventually.

Apt/Holman

Apt Corporation, 147 Sidney Street, Cambridge, MA 02139. Holman Preamplifier, $493. Three-year warranty; manufacturer pays return freight. Tested #01124 and #02060, on loan from manufacturer; also third sample, on loan from dealer.

This is one of the better preamps around, at any price, and easily the best for the money.

For a short time it was actually our reference preamp, but we ended up ranking it sonically in fifth place behind the Precision Fidelity C4, Audio Research SP-6, Mark Levinson ML-1 (very latest production only), and Hegeman HPR/CU (ditto). The first three are in a totally different price class; the Hegeman costs only about 50% more but doesn't have the Apt/Holman's control facilities.

Those control facilities are, we must hasten to add, beautifully thought out and executed with impressive quality. The L + R (in-phase blend) and L - R (out-of-phase difference) modes are alone worth the price of admission. The entire unit is well made, hand some, a pleasure to use, and quite excellent in sound. Not for nothing has Tom Holman devoted the past few years of his life to study ing, and writing about, preamplifier design. Judged against all comers, however, the Apt/Holman still falls somewhat short of state of-the-art performance. It sounds very open, smooth and balanced (the RIAA equalization is accurate); it images well (unusually good channel separation may have something to do with that); but its high-level stage does add a lit tle zip to the input signal on a bypass test, and its phono stage isn't absolutely comfortable with the most vicious leading edges traced by a fast cartridge, though better in that respect than most. In other words, it's a pretty clean preamp but not the cleanest preamp known to us.

Very important: the Apt/Holman is one preamp you should definitely keep turned on for many hours, preferably a day or more, before you judge it. Our first sample sounded absolutely awful (hard and zippy) when we first plugged it in and later improved spectacularly.

Tom Holman himself pooh-poohs this observation, but we were there and he wasn't.

Audiophiles who expressed disappointment to us about the Apt/Holman had without exception listened to it without warm-up.

Audio Research SP-6

Audio Research Corporation, 2843 26th Avenue South, Minneapolis, MN 55406. Model SP-6 vacuum-tube preamplifier, $1075. Three-year warranty. Tested #58207014 and #78307052, on loan from dealer.

The SP-6 is essentially an SP-3A-1 without tone controls and tape copy features, the only major difference being a more advanced power supply. There are also minor circuit changes, but the basic topology is the same. The sound, however, is vastly improved.

Actually, our first sample of the SP-6 sounded terrible, so bad that we returned it almost immediately. We were told it was a defective unit that had been back to the factory and inadvertently shipped out again without repair. On our test bench it didn't look obvious ly defective; in fact it appeared identical on all routine measurements to our second sample, which sounded the way we presume an SP-6 should. Just a minor mystery, but it does jibe with some persistent disagreements out there about the sound of the SP-6. Maybe, just maybe, they don't all sound the same.

Our second sample sounded excellent, we must admit. The highs were really clean; we convinced ourselves that the high-level stage was cleaner than that of the Mark Levinson ML-1, adding no trace of zip or smear on a bypass test, even with lots of high-frequency energy in the input signal. The phono stage, which is virtually identical to the high-level stage except for RIAA equalization in the feed back loop, has some problems, but it still sounds better than most phono stages. It does introduce some upper bass and lower midrange whomp, which we found much less distressing than the high-frequency garbage in nearly all transistor preamps, but that doesn't mean we condone it. This is almost surely a time-domain phenomenon, probably attributable to the feed back equalization. Not that all is well in the frequency domain; the RIAA equalization error is the worst we've ever measured in an expensive preamp: +0.75 dB (actually +0.7, -0.8), consistent in both samples. (See our remarks above about incorrect EQ networks; this is a classic case.) The resulting unbalance is clearly above the threshold of audibility; the sound of the SP-6 has a "signature" as a result.

We also measured some asymmetrical distortion on pre-equalized square waves through the phono stage; it may conceivably have been a lower threshold on this same effect that made our first sample sound distorted.

In spite of all these reservations, we rate the overall sonic performance of the SP-6, from phono input to high-level output, very high in deed. The complete freedom from dynamic stress at the higher frequencies, the superior definition of inner textures and ambience details, the general subjective impression of immediacy, the absence of burrs and gargles and other little roughnesses all add up to a very listenable preamplifier.

What's better? The Precision Fidelity C4 tube preamp, for one thing; it equals or surpasses all these virtues of the SP-6 and avoids its faults. The Cotter PSC-2 phono stage, when plugged into one of the "aux" inputs of the SP 6, makes a much more accurate phono preamp out of it. The production version of the Rappaport PRE-3 also promises to be superior. As for the Mark Levinson ML-1, the very latest factory-tweaked edition we compared against the SP-6 sounded more balanced, more neutral (no signature), tighter in the bass, but not as clean, detailed and just plain real.

That's all. No others we know of are as good.

Cotter NFB-2

Mitchell A. Cotter Co., Inc., 35 Beechwood Avenue, Mount Vernon, NY 10553. NFB-2 Noise Filter/ Buffer,

$350, with PW-2 Master Power Supply, $200. Five-year warranty. Tested #F2-124399, owned by The Audio Critic.

This is one of the new products Mitch Cotter is currently making under his own name;

it had been announced in an earlier version as the Verion NF-1, which never made it into production for legal reasons. It isn't a preamp, actually; it goes between the preamp and the power amp. Eventually it will expand into a complete system of modules powered by the PW-2 master power supply (four sockets for four modules), the sum total of which will be a super "front end" for the audio purist.

What the NFB-2 does is to keep useless and potentially disruptive subsonic and ultra sonic signals out of the power amplifier and speaker. In other words, it acts as a high-pass and low-pass filter, but of a very sophisticated variety. Ordinary bandwidth-limited devices cause time-domain changes in the signal that are audible, even though the 'corners' are out side the audio range. The NFB-2 is time domain corrected to maintain these changes below the threshold of hearing. Its low frequency corner is around 16 to 18 Hz; the high-frequency corner is somewhere between 35 and 40 kHz. The corners themselves aren't very sharp, hence our somewhat vague location of them; beyond those frequencies, however, the NFB-2 really stonewalls it. The rise time through the filter/buffer is 9 microseconds.

Mitch Cotter's rationale for the NFB-2 is (1) that the human ear is insensitive to rise times faster than approximately 14 micro seconds, (2) that no power amplifier, not even the "fastest," is really happy with superfast, high-amplitude transients, (3) that tweeter voice coils are unable to take the G forces generated by high-amplitude signals in the hundreds of kHz, (4) that there's lots of garbage below 16 Hz but no enjoyable audio information, and (5) that the DC-to-light audio design philosophy is therefore the rankest nonsense, since bandwidth limiting is possible without audible time-domain effects if the designer knows what he is doing.

Our own experience with the NFB-2 fully supports these points. We have yet to insert it into a system, no matter how well-designed or expensive, that didn't sound cleaner as a result.

The device is completely transparent, introducing no sound of its own even though it has an active stage; it's just that the rest of the system sounds clearer, sweeter, better focused with it than without it. The difference is especially noticeable on transients such as cymbal clashes; the NFB-2 takes out the lower-pitched haze, leaving only the clean metallic overtone structure of the shuddering brass. Obviously, amplifiers that are the least perturbed by out of-band transient spikes show the least difference; but even the Rappaport AMP-1, the champion in this respect, sounds distinctly better when driven through the NFB-2. The low-frequency effects are less dramatic; it's just that there are no more subsonic problems with vented speakers, no more tripping of protective circuits with thumps, pops and other low frequency transients, etc., etc.

Once again, Mitch Cotter has demonstrated to us where the real priorities are in audio. Needless to say, if preamplifiers were designed with a similar output stage, or power amplifiers with a similar input stage, there'd be no further need for the NFB-2. Fat chance.

Cotter PSC-2 (preview)

Mitchell A. Cotter Co., Inc., 35 Beechwood Avenue, Mount Vernon, NY 10553. PSC-2 Phono Signal Conditioner, $350, with PW-2 Master Power Supply, $200. Five-year warranty. Auditioned manufacturer's preproduction prototype.

This is another of the Cotter "blue bricks" that plug into the PW-2 power supply. It's an RIAA-equalized phono stage, to be connected to the "aux" input of a good (that's a must!) preamp/control unit. Eventually, Cotter will come out with such a unit; meanwhile not even the PSC-2 is out as we go to press, but we're told it will be in production before the end of 1978. This is just our initial impression of a very sloppy laboratory prototype we were allowed to borrow for a day. We had no time to put it through our usual series of tests; we simply listened.

All we can say at this point is that this may possibly be It-the preamp that does every thing better than all the others. Tremendous clarity, unlimited headroom (well over 120 dB of dynamic range is claimed), very low noise, super detail, no "character" at all, acid test for high-level stages-these were some of our observations before the prototype, put together with spit and glue, went on the blink the very next morning. That's all we can tell you; it was tantalizing and frustrating. We can hardly wait to test a production unit for real.

The Cotter PSC-2 is thoroughly un conventional in design, as you might have guessed; it acts as a current amplifier (i.e., not as a voltage amplifier), utilizing some proprietary voltage-to-current conversion circuitry and no feedback. The RIAA equalization is passive. We expect to have a full report in the next issue.

DB Systems DB-1A

DB Systems, PO Box 187, Jaffrey Center, NH 03454. DB-1A Precision Preamp, $397, with DB-2 Power Sup ply, $62. Five-year warranty; manufacturer pays return freight. Tested #1030640/2030640, on loan from manufacturer.

This is the first "official" model change in the DB-1 preamp; the A suffix signifies tighter specs on the RIAA equalization (+0.07 dB, 10 Hz to 40 kHz, it says here), fancier control knobs, conformance with the new IEC Recommendation on the "phono lo-cut" switch, and similarly trivial differences. The sound remains the same as before: slightly closed-down and just on the verge of irritating hardness, without decisively breaking through the overt annoyance barrier.

"Only three things really matter in a preamp's performance," proclaims the DB Systems small-space ad. IlI. Accuracy of frequency response. 2. Low noise. 3. Low distortion." Well, the phono equalization turned out to be almost as accurate as claimed (though no more so than that of the cheaper Series 20 Model C-21), and the noise was indeed low.

When it comes to low distortion, the small print reveals that what they mean is THD from 20 Hz to 20 kHz (less than 0.0008%-wow!) and that's all, folks. Apparently no other form of distortion exists in New Hampshire. Time dispersive distortions such as FIM and FXM must be a figment of some mad scientist's imagination. Feedback is the panacea; just pour on 40 dB more and you go from 0.08% to 0.0008%. Sancta simplicitas! We made one very interesting observation when A-B-ing the DB-1A against the Apt/Holman, with which it competes almost dollar-for-dollar in the same market. The Holman sounded cleaner and more open, but when we turned its mode switch from pure stereo to partial L + R, thereby introducing some in-phase mixing, it sounded just as closed down as the DB-1A. Subsequent bench testing revealed vastly superior channel separation in the Holman, even though the DB-1A still measured better in that respect than any actual phono cartridge known to us. But under dynamic conditions-who knows? So we still feel what we always did about DB Systems; their heart is in the right place but their ear isn't. Nor is their design rationale.

Hegeman HPR/CU (follow-up)

Hegeman Audio Products, Inc. (Hapi), 176 Linden Avenue, Glen Ridge, NJ 07028. Model HPR preamplifier with Model HCU control unit (incorporating power supply for HPR), 8720 complete. Model HPR with Model HPS power supply (phono stage without controls), $360. Two-year warranty. Tested #201/196, on loan from manufacturer.

The production model of the Hegeman preamp is even better than the preproduction unit we reported on in the last issue. The sound is beautifully open, precisely focused, and clean; there's a see-through quality that comes close to, but doesn't quite equal, what we like so much about the two tube preamps reviewed here. The very latest factory-tweaked version of the Mark Levinson ML-1 is also superior in midrange clarity, overall smoothness and that ultimate subjective impression of accuracy, but there must be a lot of ML-1's out there that don't sound as good as the Hegeman. Ours certainly didn't before it came back from its third overhaul in a year and a half.

We have a few minor quibbles about some chintzy construction details in the Hegeman, but we still consider it to be the world's best production preamplifier at a three-figure price-and, despite the recent price increase, it isn't even close to the upper three figures. Or, if you don't need any control and switching functions, the HPR/PS combination at half the price will give you the necessary phono gain and EQ straight into your power amp. All you need is a pair of SK ohm potentiometers for volume control. Stew Hegeman is even toying with the idea of offering the pots as an accessory.

Precision Fidelity C4

Precision Fidelity, 1169 Chess Drive, Suite E, Foster City, CA 94404. C4 dual-cascode preamplifier, 31095. Three-year warranty (tubes one year). Tested #2020, on loan from manufacturer.

Among the preamplifiers reviewed here, this was the last to come in, and our exposure to it has been considerably shorter than to the others (except for the previewed prototypes, such as the Cotter PSC-2 and the Rappaport PRE-3). We therefore proclaim it our top choice with some hesitation and trepidation, but we have no alternative. The Precision Fidelity C4 is simply the best, meaning the sonically most accurate and beautiful, production preamplifier known to us as we go to press.

This may very well be the last hurrah of vacuum-tube technology in preamplifier design, in the sense that the Audio Research SP-6 was announced to be but isn't. The Precision Fidelity C4 uses considerably more original circuitry and pushes the inherent audio amplification capabilities of dual triodes one step further. It has stupendous headroom; screaming sopranos, singly and massed, traced by the fastest moving-coil cartridge and fed to the phono in put through the Cotter transformer, are reproduced without the slightest sense of strain and total clarity. The entire sonic presentation can only be described as wide open from top to bottom. Sweet and smooth, yes, but also minutely detailed, precisely focused, and clean, clean, clean. In other words, it sounds real. If we have any residual criticism at all, it concerns the lower midrange, which some auditioners felt was a wee bit mushier than on the best solid-state units. It's a quibble, though, not a serious objection, in view of the absolutely convincing overall sound of the C4. If you've ever heard the Audio Research SP-6, imagine its good qualities increased and its shortcomings taken away; that's basically the sound of the Precision Fidelity C4. (But only after a good many hours of warm-up; this is definitely another unit that shouldn't be listened to cold.) Our laboratory tests were of necessity cut shorter than usual to get this review into print;

but we can at least report decent RIAA equalization (+£0.35 dB, 20 Hz to 43 kHz, but still with the typical saddle-and-hump error curve indicating the usual incorrect topology) and no obvious anomalies at first blush. The construction and parts seem truly excellent, and there's a full complement of controls and switches on a well-organized front panel. (No tone controls, however.) We shall have more to say about this exciting new product as we get to know it better; meanwhile we're definitely leaving it in our reference system.

PSH

PS Audio, 1529-C Stowell Center, Santa Maria, CA 93454. PS II Phono Preamplifier, $119.95. One-year warranty. Tested #0746, on loan from manufacturer.

This is a self-powered, RIAA-equalized phono stage, designed to be plugged into the "aux" input of a regular preamp/control unit.

PS Audio advertises it as "the world's best phono stage," guaranteed to improve even the Audio Research or Mark Levinson preamps.

We find that to be a bit over the line into taurine territory, but we must admit that for $120 the unit represents remarkable value. It is a high-fidelity preamplifier.

The sound of the PS II is somewhat hard and edgy, but no more so than that of a lot of solid-state preamps that are claimed to be SOTA and cost incomparably more. We suspect that neither PS Audio nor their clientele uses the PS II with the best MC cartridges and transformers as we did, so they probably don't know what it sounds like when zapped with accurately traced and transmitted high-frequency transients at high amplitude. It doesn't really sound pretty, not even comfort able, and some asymmetrical distortion we observed on pre-equalized square waves in the 10 to 20 kHz region may or may not be a good reason why. What the unit sounds like with in accurate cartridges we really don't care.

One thing the PS II does very well is RIAA equalization. The curve is right on the button. It turns out that the EQ network is passive, just as in the Hegeman, Cotter and latest Rappaport phono stages. That's very good company, but it doesn't quite rub off on this sassy little product, which we can recommend only on a sound-per-dollar basis to budgeteers.

Rappaport PRE-2

A.S. Rappaport Co., Inc., Box 52, 530 Main Street, Armonk, NY 10504. Model PRE-2 Stereo Preamplifier, $520. Three-year warranty; manufacturer pays all freight. Tested #1556 02, on loan from manufacturer.

The PRE-2 is the minimal Rappaport preamp, incorporating the same circuitry as the PRE-1 and PRE-1A but without tone controls.

The power supply is internal, as in the PRE-1.

Since we've already written a great deal about its predecessors, we can dispose of the PRE-2 fairly quickly.

Improvements in production engineering and quality control, plus a more directly wired signal path than in the PRE-1, actually make the PRE-2 a somewhat better-sounding unit than our previous Rappaport samples. It still has the same RIAA equalization error (-0.7 dB at 20 Hz, midbass OK, +0.6 dB from 5 to 10 kHz) and it still doesn't sound as clear, open and accurate to our ears as the latest factory updated Mark Levinson ML-1 or the Hegeman HPR/CU or even the comparably priced Apt/Holman, although it's very close to the latter (but both must be turned on for a day or two for a valid comparison). We also noticed that when we changed our reference cartridge from the Sleeping Beauty Shibata to the FR-1 Mk 3F, the PRE-2 dropped slightly in the pecking order as a result of some sonic strain its phono stage developed under the assault of those fast transients.

Everything considered, we rate the Rappaport PRE-2 among the top half dozen or so production preamplifiers today, regardless of price, which isn't bad at all considering that the far superior PRE-3 is just around the corner.

Rappaport PRE-3 (preview A. S. Rappaport Co., Inc., Box 52, 530 Main Street, Armonk, NY 10504. Model PRE-3 Stereo Preamplifier (with external power supply), $1300. Three-year warranty; manufacturer pays all freight. Auditioned manufacturer's preproduction prototype.

We heard this under almost exactly the same conditions as we did the Cotter PSC-2. A not quite perfect prototype was lent to us just long enough to listen to but not to put through our usual test procedures. Unfortunately it wasn't the same day we had the PSC-2; it would have been an interesting comparison. The new Rappaport, like the new Cotter, operates in the current mode and uses no feedback. The phono equalization is passive, just as in the Cotter. So the smartest old-timer and the brightest young whippersnapper in audio have their heads in the same place when it comes to state-of-the-art preamp design. Except that the Rappaport is a complete preamp/control unit, with all the usual functions except tone controls.

The PRE-3 also gave us the impression of a completely clean and open top, outclassing all present production preamps in that respect with the exception of the Precision Fidelity C4. It's midrange was quite possibly even clearer than that of the C4. In other words, it will be a SOTA contender for sure.

The greatest shortcoming of the PRE-3 is a relatively noisy phono stage, not nearly as low in hiss as that of the C4 or the Cotter PSC-2.

We're told that the production version will be somewhat quieter; meanwhile it's safe to predict that when all the new stuff is out and the dust settles, the PRE-3 will either win, place or show.

Series 20 Model C-21 Series 20 (a division of Pioneer Electronic Corp.), 75 Oxford Drive, Moonachie, NJ 07074. Model C-21 Stereo Preamplifier, $390. Two-year warranty. Tested #YH3600005M, on loan from manufacturer.

Pioneer's first preamp effort under their new audiophile-oriented pseudonym is a respectable one; the C-21 looks good and is extremely well built for this price range-and it even sounds decent. We can't award it any special laurels on account of a somewhat edgy and at the same time slightly nasal quality when pushed, but we've heard a lot worse for a lot more money. The flaws aren't really obtrusive; with just a wee bit more ease and plush in the sound, this could be tough competition.

We believe that the problems are in the phono stage, since the high-level stage by itself sounds surprisingly clean even when judged against all comers. On the test bench the C-21 appears to be ridiculously perfect; the RIAA equalization is actually more accurate than in the DB-1A, which tries to make a special bid for fame on that count. We could see no anomalies that would explain that touch of sonic aggression; it may be a fairly subtle feed back-related phenomenon.

One thing we liked especially about the C 21 was the 32-position attenuator-type volume control. It's the sexiest one we've ever seen on medium-priced equipment. All the other controls are also step-type and feel great. "They order these things better in Japan." Wish they would also listen more carefully.

Technics SH-901 Equalizer

Technics by Panasonic, Panasonic Company, Division of Matsushita Electric Corporation of America, 1 Panasonic Way, Seacaucus, NJ 07094. SH-9010 Universal Frequency Equalizer, $500. Two-year warranty. Tested #SGP9IB, on loan from manufacturer.

Speaking of the Japanese gulf between manufacturing wizardry and listening criteria, here's a classic case. We don't generally set much store by variable equalizers because the time-domain errors they inevitably introduce are usually more bothersome than the frequency-domain errors they're supposed to correct. But this 5-band graphic/parametric equalizer, offering variable amplitude, variable center frequency and variable Q on each band, has so much mouth-watering technology crammed into a $500 box that we just had to play with it. So we inserted it right after the preamp in our reference system and listened.

We should have known better. There's a bypass switch on the unit, labeled "equalizer in/out." Aha, we thought, we can find out right at the start whether all that mind-boggling circuitry introduces any sonic coloration of its own. We set everything dead flat on the equalizer and operated the bypass switch. No difference whatsoever either way. Must be a perfectly neutral and transparent device, right? But wait a minute, it didn't sound right either way. Everything was a little closed-down and unfocused. We pulled the wall plug of the SH 9010 with bypass switch in the "out" position.

You guessed it-the sound stopped. It wasn't a straight-wire bypass after all; there were energized circuit stages in the signal path at all times. We removed the SH-9010, reconnected the preamp directly, and there was our familiar reference sound again, open and beautifully focused.

It's not nice to fool audiophiles that way, Panasonic, and it will be a cold day in July when we can be persuaded to try a commercially available variable equalizer again.

That doesn't alter our admiration for the sheer technical ingenuity and production savvy that went into this misdirected product.

Recommendations Keep in mind that the two previewed prototype units were excluded from consideration for this list, pending full tests of the eventual production models; both, however, were sufficiently promising to be at least potential candidates for top choice in the next issue.

Best preamplifier so far, regardless of price: Precision Fidelity C4 (based on some what limited testing-see review above and future updates).

Best preamplifier per dollar: Apt/Holman (for absolute ranking, see review above).

Best way to play moving-coil cartridges:

Cotter MK-2 transformer (electrically identical and physically superior to Verion MK-1, which is no longer made).

Best interface between preamplifier and power amplifier: Cotter NFB-2.

Preamplifier Summaries and Updates All of the following preamplifiers were reviewed in Volume 1, Numbers 1, 2 or 5. Units reviewed that are of no current interest and haven't been replaced by an improved model are not listed.

Ace 3100

Ace Audio Co., 532 Fifth Street, East Northport, NY 11731. Model 3100 Stereo Preamplifier, $325 (with external power supply).

Very open, focused and detailed midrange; sizzly, nasty, almost unlistenable highs. Pity.

AGI Model 511A Audio General, Inc., 1631 Easton Road, Willow Grove, PA 19090.

Model 5114 Stereo Preamplifier, $465.

Beautiful construction for this price range; somewhat edgy and irritating sound on dynamic material, combined with a subjective effect of thinness. Not SOTA.

Audionics BT-2

Audionics, Inc., Suite 160, 10950 SW5th, Beaverton, OR 97005. BT-2 Preamplifier, $449 (with handles on front panel, $459).

Best preamplifier per dollar the last time around; nosed out by the Apt/Holman in our latest tests. Open, smooth, focused, lacking only the ultimate immediacy and super detail. A new modification, to be out soon, is claimed to be considerably superior.

Audio Research SP-3A-1

Audio Research Corporation, 2843 26th Avenue South, Minneapolis, MN 55406. Model SP-3A-1 vacuum-tube preamplifier/control: no longer available in the version reviewed.

If you own an SP-3, SP-3A or SP-3A-1, you can have it modified by Audio Research "to upgrade it to the SP-6 level" (it says here). The cost is $470. The mod will presumably give you the SP-6 kind of sound, plus tone controls and tape copy features. The SP-3A-1 we originally tested had much more aggressive and less natural highs than the SP-6.

Audio Research SP-4

Audio Research Corporation, 2843 26th Avenue South, Minneapolis MN 55406. Model SP-4 solid-state preamplifier: no longer available in the version reviewed.

The original SP-4 we tested sounded open, clear, but hard and sibilant. The bass was somewhat deficient. Now there's a new SP-4A at $975, which we haven't tested. The SP-5, at $595, appears to be the same thing without tone controls.

Bravura Audio Arts, 4208 Brunswick Avenue North, Minneapolis, MN 55422.

Bravura Stereo Preamplifier, $495.

An astonishingly wrongheaded design, full of little cultist quirks. Sounds like a transient filter; no sparkle, no life.

CM 300

Audio International, Inc., 3 Cole Place, Danbury, CT 06810. CM 300 Stereo Control Center, $549.

Forget it; not in the same class with any number of more recent units selling at lower prices.

Cotter MK-2

Mitchell A. Cotter Co., Inc., 35 Beechwood Avenue, Mount Vernon, NY 10553. Moving-Coil Pickup Transformer MK-2, $425.

The laws of physics strongly suggest that a textbook perfect transformer will outperform a textbook-perfect active device (pre-preamp or head amp) when it comes to interfacing a low-impedance moving-coil pickup with subsequent stages of amplification. The Cotter MK-2 transformer begins to approach the aurally perceptible thresholds of such textbook perfection; certainly no active device known to us is as quiet or as close to a straight wire in its sonic character. Mitch Cotter's original Verion MK-1 transformer was electrically identical but is no longer made; the new MK-2 incorporates some minor improvements in physical construction, including better plugs.

Dayton Wright SPS Mk 3 Dayton Wright Associates Limited, 350 Weber Street North, Waterloo, Ont., Canada N2J 4E3. SPS Mk 3 Professional Preamplifier, 8555.

Sounded reasonably smooth and detailed, though a bit closed down, when we tested it; however, this company has changed hands since-so who knows? The RIAA equalization was quite inaccurate on our test sample.

Dynaco PAT-5

Dynaco, Inc., Coles Road & Camden Avenue or PO Box 88, Blackwood, NJ 08012. PAT-5 Preamplifier: no longer available in the version reviewed.

The current version is the PAT-5 Bi-FET at $299 (kit only); the original version we tested sounded absolutely horrible. Variability of parts has been the bugaboo of this line.

GAS Thaedra, Thoebe, Thalia

The Great American Sound Co., Inc., 20940 Lassen Street, Chatsworth, CA 91311. 'Thaedra' Servo-Loop Preamplifier: no longer available in the version reviewed. 'Thoebe' Servo-Loop Preamplifier, 8599. 'Thalia' Servo-Loop Preamplifier, $339.

Thaedra II, at $1049, replaces the original version we tested. Thoebe (same thing minus MC head amp) remains as before; so does Thalia. We're not too fond of the design philosophy and listening criteria of this company, although we see some recent evidence that they're having second thoughts.

We don't consider any one of these preamps to be a good buy at its particular price point; all have a veiled, hazy, smeared-over sound quality indicating serious time-domain problems.

Hafler DH-101

The David Hafler Company, 5817 Roosevelt Avenue, Pennsauken, NJ 08109. Model DH-101 Stereo Preamplifier, 8299.95 wired. (In kit form, $199.95.) After having examined and lived with two additional samples of this preamp, we're ready to concede that the deterioration of our original review sample after prolonged "cooking" on our equipment rack was untypical. These last two samples continued to produce open, spacious, balanced, well focused sound week after week, with just a slight cutting edge when pushed hard with a superfast cartridge. We really can't think of more than six or seven production preamplifiers, at any price, that we'd currently rate superior to the DH-101. At its price, either wired or as a kit, nothing can touch it. We still don't like those 0.01 microfarad bypass capacitors on the AC line; they're a shock hazard and a source of hum. In general, the unit is quite prone to hum in some installations because of its peculiar grounds. Even so, it's an honest and intelligent product, representing good value.

Hegeman HIP Input Probe Hegeman Audio Products Inc. (Hapi), 176 Linden Avenue, Glen Ridge, NJ 07028. Model HIP Input Probe with HPS power supply, $160.

This is essentially the unequalized input stage of the complete Hegeman preamplifier, made available here on a separate mini-chassis. It acts as a plug-in interface between the phono cartridge and your present phono input. If the latter is in correctly designed (e.g. Audio Research SP-4), the Input Probe will effect a definite improvement in sound. Our recommended preamps, on the other hand, don't need it.

Linn Moving Coil Preamp

Audiophile Systems, 5750 Rymark Court, Indianapolis, IN 46250.

Linn/ Naim Type PNAG moving coil preamp with Type NAPS power supply, $250.

Not as neutral, transparent and low in noise as the Cotter (formerly Verion) transformer but less veiled and colored than other pre-preamplifiers known to us.

Luxman C-1000, CL-35/III, CL-350 Lux Audio of America, Ltd., 160 Dupont Street, Plainview, NY 11803.

Model C-1000 Control Center: no longer available in the version reviewed. Model CL-35/III Vacuum Tube Control Center, $795.

Model CL-350 Solid State Control Center: no longer available in the version reviewed.

The sound of the original C-1000 was closed-down and at the same time slightly aggressive; we have no idea what its cheaper replacement (C-1010, $745) sounds like. The CL 35/III, still in the line, is a decent tube preamp but not in a class with our present top choices. The defunct CL-350 appears to have no direct descendant; in its time it sounded hard, nasal and ugly.

Marantz 3600

Superscope, Inc., 20525 Nordhoff Street, Chatsworth, CA 91311.

Marantz 3600 Stereo Control Console, $499.95.

Unbearably aggressive highs; forget it.

Mark Levinson ML-1

Mark Levinson Audio Systems, 55 Circular Avenue, Hamden, CT 06514. ML-1 Preamplifier, with plug-in System A, $1850. (Plug-in System D for MC cartridges, $240 extra.) We still don't know of a solid-state preamplifier in actual production that equals this one in clarity, smoothness, balance, and low noise; the Precision Fidelity C4 and Audio Research SP-6 tube preamps, however, are definitely cleaner, more transparent, more effortlessly natural in sound, though not as quiet. The new current-mode feedback-less preamps (Cotter, Rappaport) will undoubtedly be the future threats to the supremacy of the ML-1 in the solid-state category. Our own sample has undergone three factory overhauls in a year and a half, each time because we suspected a slight lapse in performance; each time it came back sounding considerably better and ranking higher in our comparative tests. The latest update involved replacement of our very early phono input modules and applying shielding to some previously unshielded sections of the switch wiring. Before these changes both the production Hegeman and the Apt/Holman sounded more open and better focused. We can only speculate whether or not all this is typical of other samples in the field.

Paragon Model 12 Paragon Audio, 997 East San Carlos Avenue, San Carlos, CA 94070.

Model 12 vacuum-tube preamplifier: no longer available in the version reviewed.

This was the best tube preamp of its time, quite com parable to the top solid-state units and barely nosed out by the then new Mark Levinson ML-1. We haven't tested its successor, the Model 12A ($1045); meanwhile the rumor is that this company has folded. What a shame.

Quad 33

Acoustical Manufacturing Co. Ltd., Huntingdon, Combs. PEI8 7DB, England.

Quad 33 Control Unit, $295.

Respectable sonic performance and unusually clever variable high filter; the Hafler DH-101, however, offers tighter, better focused sound at the same price.

Rappaport PRE-1 and PRE-1A A.S. Rappaport Co., Inc., Box 52, 530 Main Street, Armonk, NY 10504. Model PRE-1 Stereo Preamplifier, $620. Model PRE-1A Stereo Preamplifier, $555, with PS-1 Power Supply, $200, and optional MC-1 Moving Coil Phono Stage, 3300.

We refer you to the Rappaport PRE-2 review above; the PRE-1 and PRE-1A have tone controls but are otherwise the same preamp. The MC-1 is far too noisy for our taste and its RIAA equalization error is too large for comfort.

Stax SRA-12S

American Audioport, Inc., 1407 North Providence Road, Columbia, MO 65201.

Stax SRA-12S integrated preamplifier/headphone amplifier, $500.

We saw this listed some time ago with an RII suffix; we're sure it's still essentially the same unit we tested. We didn't like the preamp section at all; it sounded hard and sizzly on dynamic material. The headphone amplifier section also disappointed us in the long run.

Supex SDT/180 Sumiko Incorporated, PO Box 5046, Berkeley, CA 94705. Supex SDT/180 Step-Up Transformer, latest price NA (was $150).

We prefer transformers to pre-preamps for moving-coil cartridges-but not like this. Rolled-off bass and distorted to boot.

Van Alstine Model One

Van Alstine Audio Systems, Inc., 12217 Riverwood Drive, Burnsville, MN 55337. Model One direct-coupled stereo preamplifier, $600.

Highly touted but far from SOTA. The sound is open and essentially neutral but still a bit grainy, edgy and irritating. The phono stage shows some anomalies on square waves.

Verion MK-1 Superseded by Cotter MK-2 (see above).

Yamaha C-1 and C-2 Yamaha International Corp., 6600 Orangethorpe Avenue, Buena Park, CA 90620. NS Series C-1 Stereo Preamplifier, 31800. NS Series C-2 Stereo Preamplifier, 3650.

The C-1 was an overpriced PR stunt for image building; it's no longer on the market. The sound was smooth but closed down and lacking in inner detail. The C-2 was (or is, if it's still around) beautifully built for the money, very low in noise, but impossibly sizzly and aggressive on high-frequency transients.

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[adapted from TAC]

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Also see:

Cartridge/Arm/Turntable Follow-Up: Loose Ends and New Developments

Various audio and high-fidelity magazines