More and Better Preamplifiers (Again and Again) (Vol.2, No.1: Winter/Spring 1979)

An overwhelmingly superior SOTA preamp, an old favorite up dated to near-SOTA and best per dollar, and the cheapest of them all improved beyond the previous best buy-this is a fast track indeed. Maybe the fastest in all audio.

Because of the excruciatingly detailed coverage of preamplifier design theory in our State of the Art seminar, both in Part I of the transcript in this issue and in the coming Part II, we wish to avoid driving the subject into the ground and shall therefore forgo our usual pre amble to the reviews.

Just one small gloating chortle before we get down to business. It looks like that silly IEC playback equalization change has been laughed out of existence by those who knew better all along and said so-including this journal. We haven't seen it come up in new designs lately.

Requiescat in pace.

The following preamps were all evaluated on the basis of bench tests discussed in previous issues and by insertion into our Reference A system for A-B listening comparisons.

Audionics BT-2 Series II

Audionics, Inc., Suite 160, 10950 SW 5th Avenue, Beaverton, OR 97005. BT-2 Series II Preamplifier, $459 (with front-panel handles). Three-year warranty. Tested #02962, on loan from manufacturer.

This “improved” version of the BT-2 can be distinguished from its predecessor by its gold-plated phono inputs and main outputs, plus a pair of -12 dB secondary outputs. The principal design change is a new regulated power supply; the wiring harness is also somewhat different.

We have no idea what else they did to this basically very decent preamp, which was our best-per-dollar selection only two issues ago, but we don't like the new sound. The only fault of the original BT-2 was the lack of ultimate de tail, but its basic sonic quality was very smooth, balanced and listenable. The Series II, on the other hand, sounds hard, edgy and zingy. It grates on the ear, regardless of output level.

Our laboratory tests revealed no correlation with this finding; everything looked very acceptable, including pre-equalized square waves through the phono stage. The RIAA equalization isn't perfect below 200 Hz, mainly on account of the retention of the nonsensical IEC roll-off feature from the older BT-2. In the new “filter defeat” position of the switch, a little bit of the roll-off still remains (-1.25 dB at 20 Hz). Above 1 kHz, the curve is right on the nose. All in all, not one of this excellent company's best efforts.

CM 301

Audio International Inc., 3 Cole Place, Danbury, CT 06810. CM 301 FET Preamplifier, $279. Three-year warranty. Tested #376, on loan from manufacturer.

Here's a case where nothing seems to be quite right. CM Labs claims that the 301 uses state-of-the-art circuitry and insinuates that the low price is due merely to the simple, straight line, minimum-control design. We, however, find both the sound and the measurable characteristics unacceptable.

Intolerably hot, piercing highs and a homogenized, poorly detailed texture characterize the sound of the CM 301. The bottom end is diffuse, and there's a general lack of coherency throughout.

On the test bench there are similarly disturbing anomalies. The phono stage appears to handle transients asymmetrically when driven hard and the high-level stage is prone to peculiarly abrupt hair-trigger clipping once it runs out of headroom (of which it has plenty, though). Could be the feedback blues. The RIAA equalization error is one of the worst we've seen lately: +1.0 dB at 30 Hz, 0 dB from 200 Hz to 1 kHz, +0.5 dB from 5 kHz all the way up to 20 kHz. In other words, the bass and treble controls are up, even though the CM 301 doesn't have any. Need we say more? Next!

Cotter PSC-2 and CU-2

Mitchell A. Cotter Co., Inc., 35 Beechwood Avenue, Mount Vernon, NY 10553. PSC-2 Phono Signal Conditioner, 8475; CU-2 Control Unit, $1350 (projected price of forthcoming production version); both with PW-2 Master Power Supply, $250. Five-year warranty. Tested PSC-2 #C2-128410 with PW-2 #P2-128449, own ed by The Audio Critic, and limited-production “engineering model” of the CU-2.

The five modules of Mitch Cotter's monumental 3-k$ “front end”-which he calls System 2 and includes his moving-coil pickup transformer, phono stage, control unit, noise filter /buffer, and power supply-can now be all hooked up together and auditioned, which is what we've been doing for some time (see also the reference system article in this issue). We can confidently report that nothing we've ever listened to during our 30 years in audio is in the same class sonically. Mind you, we've owned some truly superior preamps-by Audio Re search, Hegeman, Saul Marantz, Mark Levin son, Rappaport and others-and each time it seemed that further improvement would have to come from elsewhere in the chain because the preamp was just about perfect. Well, it wasn't.

Little flaws and glitches and obscurations attributed to the pickup, the record, the speaker, and so forth, came from the preamp after all.

Because now they're gone. There's nothing but uncanny quiet and total transparency, coupled with unlimited dynamics.

That said, we must issue a few words of caution. The Mitchell A. Cotter Company is a recently formed, small and not very heavily capitalized operation, still in the teething stage as a business and, in addition, scarred by its rather traumatic separation from Verion Audio. Production has been slow, painful and somewhat unpredictable, although four out of the five System 2 modules are now in their absolutely final form and being made in small quantities every day. That much we know. The CU-2 in its production version has yet to be seen; several dozen of the electrically identical but cosmetically primitive “engineering model” have been circulating for some months, how ever. The point is-don't get mad if your now aroused desire for this equipment can't be instantly gratified, even if you walk into the store with a bundle of cash. Especially, don't get mad at The Audio Critic! Don't write us letters. We have absolutely no control over the operation of this company. All we can tell you is that, if and when you do manage to take home a piece of Cotter equipment, it will perform exactly as claimed. What's more, it will be built like a battleship, with nothing but mil-spec parts in it, ready to survive on the moon if necessary. For example, nobody but nobody in consumer audio uses the kind of heavy-duty, broadcast type step attenuator that controls the output of the CU-2. It must cost the manufacturer some thing like $100.

Since we've already reviewed the Cotter transformer and noise filter /buffer, which have no counterpart in competitive preamps, let's just consider the PSC-2/CU-2/PW-2 combi nation, constituting what is traditionally considered a complete preamplifier. At just a little over $2000, it's not even the highest priced ex ample of the breed, although it isn't exactly cheap. What it will immediately do upon insertion into your system-and your system had better be a very good one, with the pickup perfectly aligned laterally and vertically-is to make you wonder where everybody has been. If this is what the record really sounds like, then what did-and do-all those other preamp designers have in mind? Is it possible that nobody but Mitch Cotter is conversant with the ultimate realities of phono playback? One should hope not, but then what's going on? The fact is that we've already begun to notice some frustration, jealousy and resentment out there in guru country about this very subject. Just re member that we're merely reporting what our ears tell us, without the slightest concern for repercussions in the fraternity house of high end audio.

According to Mitch Cotter, the unique clarity and unstrained headroom of his preamp are due to relentlessly straightforward applications of basic principles rather than any kind of engineering wizardry. The signal is amplified in the current mode, as it is less vulnerable to contamination that way than in the voltage mode, and there is no inverse feed back loop anywhere in the circuit. Balanced line symmetry is maintained from input to out put. The stage of gain in the CU-2 is identical to that in the PSC-2, the only difference being the passive RIAA equalization in the latter. The conversion of current back to voltage in each circuit module is totally unorthodox but it works very simply and beautifully. The CU-2 has an unusually complete range of controls, one of the most useful of which is 180° phase reversal, separately controllable in each channel. (See the note on absolute phase elsewhere in this issue.) On the lab bench, the behavior of the entire system is flawless, requiring no specific comment. We can't trip it up with any test known to us. The RIAA equalization is 100% accurate.

There's really nothing else left to say. If you can afford the Cotter preamp, get it. If you can't, at least go out and listen to it in a good system. It's an education.

Dyna mod:

FET-5 Mark V

Jensens Stereo Shop (Frank Van Alstine), 2202 River Hills Drive, Burnsville, MN 55337. FET-5 Mark V preamplifier, 8399 (when built new from Dyna PAT-5 Bi FET kit). Mod kits, updates of older PAT-5 mods, etc., also available. Tested mod of original PAT-5, owned by The Audio Critic.

Frank Van Alstine has been modifying Dyna PAT-5's and PAT-5 Bi-FET's since the earliest memory of man. This is the latest mod we've been able to test; undoubtedly, by the time we're in print, there will be a Mark VI. You can make book on it.

This particular mod bypasses the tone controls and a few other functions of the PAT-5 in a professed attempt to achieve state-of-the art performance on straight-through phono playback. The attempt is unsuccessful. The FET-5 Mark V betrays obvious colorations from the very start when A-B-ed against top quality preamps. In the midrange, especially, there's a strangely hooded quality. We must admit, however, that there's no edginess.

The midrange also looks peculiar on pre equalized square waves through the phono stage. A 500 Hz square wave, for example, which should have an almost perfectly flat top in this test, shows a shallow S-shaped top in stead. The RIAA equalization error curve is humped up +0.4 dB at 200 Hz and +0.3 dB at 10 kHz, which isn't state-of-the-art, either.

There also seems to be some oscillation at a very high frequency on square waves through the high-level stage. Maybe the thing is too wideband (rise time 250 nanoseconds-what for?). In this instance, we can't recommend Frank Van for Ludwig van.

Hafler DH-101 (Improved, with DH-102)

The David Hafler Company, 5817 Roosevelt Avenue, Pennsauken, NJ 08109. Model DH-101 Stereo Pre amplifier, $299.95 wired. (In kit form, $199.95.) Model DH-102 Moving-Coil Pre-preamplifier, $74.95 (fully assembled, to be connected inside DH-101). One-year warranty. Tested factory-modified sample, on loan from manufacturer. As of May 1, 1979, beginning with serial number 1919000, all Hafler DH-101 preamps shipped, whether kit or wired, incorporate certain electronic improvements. The sound is considerably more three-dimensional, transparent and detailed than before, with the occasional hardness and edginess of the original version significantly reduced. (The RIAA equalization peculiarities are the same as before, though.) We marginally preferred this improved DH-101 to the Hegeman preamp reviewed in the last issue (not the greatly improved Hegeman reviewed below), which is high praise indeed for a $300 preamp. At one point we were strongly considering the improved Hafler as our new Reference B selection but ended up filling that slot at a much higher price level. Even so, this unit has class, and we recommend it highly.

We can't say the same for the neat little DH-102 pre-preamp that fits right inside the DH-101 and is nourished by the same power supply. It sounds much too bright, zippy and fatiguing to be our recommendation even for a minimal moving-coil phono system. Try the Marcof PPA-1 instead.

Hegeman HPR /CU (Improved) Hegeman Audio Products, Inc. (Hapi), 176 Linden Avenue, Glen Ridge, NJ 07028. Model HPR pre amplifier with Model HCU control unit (incorporating power supply for HPR), also known as Hapi One, $720 complete. Two-year warranty. Tested #260/238, on loan from manufacturer.

This is a very short and sweet story. Stew Hegeman decided he wasn't 100% satisfied with the Hapi One preamp we've been talking about for the past two issues, took some gain out of the phono stage, added that much gain back to the high-level stage, made a few other minor circuit improvements, and changed the face plates from black to silver. The result is a totally-and we mean totally-different preamp.

The improved Hapi One, at $720, is in our opinion the best-sounding phono preamp in the world after the $2000-plus Cotter and there fore the greatest preamp bargain in existence despite its still rather high price. In openness, solidity, precise spatial imaging and fuzzless definition it outdoes some of the most revered names in preamps, costing several times its price. Its edgeless highs and tight bass are most impressive, and only when A-B-ed against the incredibly transparent Cotter does it appear the least bit veiled. The $1300 Rappaport PRE-3 also has a more transparent high-level, but not phono, stage.

On the test bench, the basic characteristics of the preamp are as before. Note that the new silver faceplates also identify retrofitted samples, just as they do the new production model, because whenever the innards are up dated on an older unit the faceplates are automatically changed.

And that's not all. The Hapi Two, with the identical circuitry and controls but stunning new all-in-one cosmetics, is just about to make its debut. Its ultraflat “pancake” relay-rack chassis and stylish front panel are as sleekly glamorous as the Hapi One is drab and utilitarian. Clever shoehorning has made the previous two-chassis construction unnecessary, we're told; the hum is even lower than before. The projected price is $900. So, 30 years after the marvelous but shockingly ugly Lowther-Hegeman horn speaker, it looks like Stew Hegeman has his whole act together.

Hitachi HCA-7500

Hitachi Sales Corporation of America, 401 West Artesia Boulevard, Compton, CA 90220. Model HCA-7500 stereo preamplifier, $370. Tested #8001053 G, on loan from dealer.

A young American manufacturer of esoteric audio components looked at this preamp on our test rack and shook his head: “I don't know how they do it.” The HCA-7500 looks like $800's worth of equipment at the very least, with its highly authoritative black control panel, solid-feeling knobs and switches, and mind-blowing variety of functions. And for a $370 preamp it sounds great, too. There's just a touch of zippiness in the midrange and highs, quite a bit short of an objectionable edge, and the overall sound is strikingly open and detailed. For a while we hesitated between the HCA-7500 and the newly improved Hafler DH-101; we finally decided that the latter with its somewhat smoother highs would be the better choice for the audio purist on a budget, even though it sounds slightly “rounded off” in detail next to the Hitachi.

Our laboratory tests revealed no vices; we were particularly impressed with the virtually perfect RIAA equalization. If this is a fore taste of what is to come from the Japanese giants as they become more interested in the sophisticated audiophile market, some of the small American firms that cater to the latter had better look to their laurels. An outfit like Hitachi is capable of doing just about anything they choose to do and package it at just about any price they feel like.

Mark Levinson LNP-2

Mark Levinson Audio Systems, Ltd., PO Box 6183, Hamden, CT 06517. LNP-2 Preamplifier, $3500 (plus special options, if any). Five-year warranty, customer pays all freight. Tested #2018, owned by The Audio Critic.

We own this superbly built, virtually indestructible professional control unit as a necessary extension of our Mark Levinson ML 5 master recorder system, which uses the Studer A80 tape deck and MLAS electronics.

We wouldn't dream of owning it, for purely audiophiliac purposes, as the phono preamp of some kind of super system. Since a number of audiophiles to whom price is no object might be tempted to do exactly that, we feel the obligation to evaluate the LNP-2 very briefly on the basis of its essential sonic quality, without reviewing it at this time as a tool for the recordist. (This issue is already much too fat for that.) Basically, the LNP-2 has a very clean, firm, open and well-controlled sound, without any irritating edge. A couple of years ago this would have been considered definitely SOTA.

Next to the Cotter, Hegeman, Precision Fidelity C4 and Rappaport PRE-3, however, the LNP-2 appears to have slight colorations as well as an overall “homogenized” quality that submerges ultimate detail. This is true of both the phono stage and the high-level section; in fact we were quite surprised that the latest Hegeman HCU control unit, which isn't quite straight-wire-like either, changed the sound of a line-level source a lot less on a bypass test than the back end of the LNP-2. Time marches on.

As a result of these findings, we decided not to make the LNP-2 the nerve center of our reference system through which line-level signals would be routed. Too damn bad, be cause with its meters and calibrated controls it would have been ideal for that job.

Precision Fidelity C4 (Improved)

Precision Fidelity, 1238 Green Street, San Francisco, CA 94109. C4 dual-cascode preamplifier, $1095. Retrofitting original unit to new configuration, $75. Three-year warranty (tubes one year). Tested retrofitted sample, on loan from manufacturer.

Beginning with serial number 4000, the C4 vacuum-tube preamp comes with 10 dB less feedback in the phono stage, 10 dB less feed back in the high-level stage, an improved input selector switch, and other minor changes. The sound is even more open, detailed and dynamically alive than before, but meanwhile other good things have happened, and we can no longer make the C4 our Reference A choice.

The new Cotter preamp is in a totally different class, and even the considerably less costly Hegeman, in its latest version, sounds smoother on top and firmer in the bass. By comparison, the highs of the C4 have a tiny bit of shimmery coloration and the lows are on the loosey side. But, we must repeat, only by comparison against the best. The C4 is still one hell of a preamp.

We find it regrettable, though, that Precision Fidelity didn't use the opportunity of the design update to correct the saddle-and-hump error curve of the RIAA equalization. In fact, it's a little saddlier and humpier than before: -0.6 dB at 175 Hz (in the worse channel) and +0.35 dB at 10 kHz. Despite that, if you bought a C4 on the basis of our recommendation, we feel you should spend the $75 the manufacturer charges for the retrofitting. It's definitely worthwhile.

Rappaport PRE-3

A.S. Rappaport Co., Inc., Box 52, 530 Main Street, Armonk, NY 10504. Model PRE-3 Stereo Preamplifier (with external power supply), 81300. Three-year warranty, manufacturer pays all freight. Tested early production sample, on loan from manufacturer.

After our rather enthusiastic preview of the PRE-3 in the last issue, it will probably strike you as anticlimactic that, even though we find the sound of the production version quite excellent, we just can't live with that noisy phono stage.

Since we didn't have the early prototype side by side with the production model, we can't tell you whether the latter is a little quieter, as had been promised. All we can tell you is that it isn't quiet enough. The hiss intrudes at all times and submerges delicate details of texture and dimensionality. We found ourselves unable to listen “through” it undisturbed; to the extent we could do that, we found the sound of the phono stage very good but not as transparent or revealing, we felt, as that of the Cotter PSC-2 or even as satisfying overall as that of the Hegeman HPR. But we certainly can't defend too vigorously any perception based on such an artificial separation of subjective criteria.

The technical reason for the hiss is passive bandwidth limiting right at the phono input, be fore the first active stage; all the high-frequency noise of the cascaded active stages comes out the back of the preamp unimpeded, right on top of the phono signal. Andy Rappaport believes that this is the only way to implement his basic concept of a no-feedback preamp and that the issue isn't negotiable. To us that's something of an orthodox Marxist attitude; the political dogma isn't negotiable even when the net result is bread lines. Or, in this case, noise.

To complicate the matter, the RIAA equalization of the PRE-3 is quite inaccurate; there's a -0.5 dB saddle at 150 Hz, a +0.5 dB hump at 4 kHz, a -1.0 dip at 20 kHz, continuing to -2.5 dB at 43 kHz. That nudges the threshold of audible colorations. Harmonic distortion is a whole order of magnitude higher than in conventional feedback phono stages, but that doesn't bother us in the least. (See also our re view of the Rappaport power amp in this issue.) We must add that none of the above criticism applies to the perfectly quiet high-level stage of the PRE-3, which approaches straight wire transparency on a bypass test and must be considered in the same class with the Cotter CU-2. But not many people buy a phono preamp for its “aux” sound.

We're hoping that one day Andy's dogmatism will mellow and he'll redesign that phono stage. Then the PRE-3 will be a killer.

Spatial Model TVA-1

Spatial, Inc., 3633 Long Beach Boulevard, Suite C, Long Beach, CA 90807. Spatial Coherence Preamplifier, Model TVA-1, $1195. Three-year warranty; customer pays all freight. Tested #00291 and #00496, on loan from manufacturer.

We liked the original version of the Spatial well enough to have used it as our temporary Reference A preamp while our Precision Fidelity C4 was being retrofitted and before the arrival of the latest Cotter and Hegeman units.

We thought the highs were very suave and finely detailed, and the overall sound quite realistic in openness, depth and three-dimensional imaging. At the same time we noticed a somewhat thick, gagged quality in the midrange, which bothered us from time to time. We then switch ed to the Mark Levinson LNP-2, the only other good preamp we had available at the time, and the midrange opened up but the texture be came somewhat more homogenized.

The company then informed us of a major sonic improvement and swapped our unit for one of the new ones. The midrange of the latter sounded considerably thicker and more stuffed up; if the first one had a wiener in its mouth, then the new one had a hero sandwich or a whole salami. This wasn't even close to reference quality. Spatial's explanation was that a few units had certain elusive problems originating from the new high-intensity neon pilot light; if we disconnected it the midrange would clear up. This sounded like sheer cultist dementia to us but we tried it anyway. Since the chassis is deliberately designed like a Chinese puzzle to prevent people from taking a peek in side (more about that in a moment), we had to take off and later replace all the eight knobs on the unit plus countless screws in order to get at the bulb. You guessed it-the sound remained unchanged, and we felt like someone who had knowingly sat down on the whoopee cushion planted by the kids, just to let them have their little joke.

On the lab bench both samples behaved in exemplary fashion, with very low distortion figures even at unusually high output levels, excellent square wave response both through phono and high-level, and accurate RIAA equalization. No clue whatsoever to the sonic anomalies.

Of course, anything but the most obviously audible superiority to all other preamps in the world would be incompatible with the introductory ballyhoo about the Knapp TFET-Valve used in the Spatial. This is supposed to be a revolutionary device that's more linear than any vacuum tube, bipolar transistor, field effect transistor or anything else that amplifies.

But what is it? Ah, they won't tell you. They don't even want you to look; that's why the pre amp is fitted and screwed together the way it is and sealed with an initialed tab. If you do succeed in laying eyes on the forbidden sight, you'll instantly think of the Audio Research “Analog Module,” a hype of almost equal effrontery.

The TFET-Valve is the same kind of potted circuit module-just a small block of epoxy. The words “patent pending” appear only once as a footnote in all the Spatial literature that mentions the TFET-Valve, and even there in a different typeface, tacked on as an obvious after thought. No one we know has ever seen or even heard of any written material on such a patent.

No one knows what's buried in the epoxy.

No other electronic product in the world uses the device to our knowledge. Mighty peculiar for a revolutionary invention.

A half-technical, half-popular treatise by Richard P. Knapp on “spatial coherence and the TFET-Valve amplification process” was circulated long before the introduction of the preamp; it's an obscurantist, evasive piece of writing that couches familiar knowledge about time-dispersive distortions in the less familiar language of information theory and other disciplines. It's basically hamburger served as “Salisbury steak” by someone who doesn't want you to know it's hamburger.

All this devious manipulativeness and cultist posturing, combined with an apparent dismissal of the consumer's ability to think, cannot fail in the end to turn off the best people in audio, the very element that constitutes Spatial's potential following. We're already beginning to see some evidence of that. Actually, with all the preamp's faults, we like it a lot better as a product than we do the company's image itself.

Recommendations

Two issues ago, we made some remarks here about not expecting any changes in our top recommendations in the foreseeable future.

And you know what happened in the very next issue. This time we'll be smarter and just name our current choices.

Best preamplifier so far, regardless of price: Cotter System 2.

Best preamplifier per dollar (and, incidentally, the next best regardless of price):

Hegeman HPR/CU (Hapi One).

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[adapted from TAC]

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Also see:

The Two Most Interesting Power Amplifiers for the Audio Purist: Hafler DH-200; Rappaport AMP-1 (follow-up)

Various audio and high-fidelity magazines