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LISTENING TESTS ON THE JUNG-WHITE PAT-5/WJ-1A by DAVID VORHIS Issue 3/79 of TAA contained Walt Jung's and Dave White's article on their latest modification of Dyna's PAT-5 preamp. Actually, they described several levels of modifications and noted the sonic advantages (or disadvantages) of each. The unit I auditioned had the most extensive modifications, what the authors call the PAT-5/WJ-1A. Obviously, my comments on sound quality relate only to that level of modification. I can't say how it differs in sound quality compared to the other versions, the original PAT-5/W]-1 (TAA, 1/78), or a stock PAT-5. The equipment and procedures I used in evaluating the WJ-1A are virtually identical to those I used for the Hafler preamp (744 3/78) and the Lampton-Zukauckas Mark I (TAA 1/79). My only procedural change was in evaluating the WJ-1A as a complete unit, i.e., phono input to high-level output, since Walt indicates that the input switching circuitry (which can be bypassed only for the phono input) degrades the sound. I also borrowed a Hafler preamp from a friend for comparison, burning in both units for over 24 hours before listening. My primary reference preamp was a home-built tube unit using a high-gain cascode phono stage. In normal operation, my power amp is fed directly from the volume control following the phono stage. In my opinion, the WJ-1A's most impressive characteristic sonically is its reproduction of deep bass. In this range, the WJ-1A has superb detail and impact. The preamp seems to grab the woofer and force it to respond exactly to the music, with no hangover or heaviness. The WJ-1A has the most accurate deep bass of any preamp I have ever heard. The mid and upper bass, however, is extremely lean, which thins out some of the richness in well-recorded music. Perhaps this effect is directly related to the tight deep bass. In any case, I suspect it will actually complement most dynamic woofers since they are typically loose or fat in the mid or upper bass. In the mid-range the WJ-1A has excellent musical detail and it is smooth and unstrained at all signal levels. It is not recessed like the Lampton-Zukauckas Mark I, but it is missing a certain warmth and sweetness evident on the best tube preamps. Like the lean quality in the mid and upper bass, this is certainly not a major failing but it is audible and it makes the WJ-1A sound somewhat "electronic.'' I think the best way to describe it is that the WJ-1A removes some of the warmth and sweetness from the input signal, whereas many tube preamps add these qualities. The highs on the WJ-1A are open and airy. There are simply no ''burrs'' or discontinuities in the high end. In this regard it is similar to the Mark I and quite unlike the Hafler. The extreme highs may perhaps have an added shimmer, but this effect may be due solely to its superior transient response. The overall tonal color of the WJ-1A is neutral. In fact, it reveals colorations in other preamps immediately. .Its only colorations result from the slightly recessed upper mid range and mid to upper bass, and these are by no means offensive. For some reason, and I haven't the slightest idea what it is, nearly all solid-state preamps seem to me to compress dynamic peaks. They simply don't get as loud as a high quality tube preamp, even though they may be set for identical gain. As I noted in the Hafler review, that design is a notable exception in that it actually has better dynamics than my tube amp, except on very loud peaks where it becomes somewhat frazzled. I never heard the WJ-1A sound frazzled, but its dynamic characteristics are slightly compressed. It is no worse in this respect than most solid-state units and, in fact, it is considerably better than the Hafler Mark I. Nevertheless, I believe this makes the WJ-1A sound less ''alive'' than the Hafler or my tube preamp. Unlike most high-definition solid-state designs, the WJ-1A's imaging is not etched where each detail is vividly carved into space. The WJ-1A is, to my taste, more natural. The lateral imaging is fairly precise although it is not as stable as my reference preamp. Some listeners may find that the high-level stage of the WJ/1A is fairly noisy in their system. This was the case in mine. Connecting the WJ-1A to a Williamson Twin Twenty and Fried H speakers resulted in a hiss level easily audible from my listening chair some 12 feet from the speakers. The noise didn't intrude on the music since it was masked by record noise, but I did find it distracting. Switching to a Dyna MK IV (substantially modified but with stock sensitivity-1.3 volts input for 40 watts output) reduced the noise level significantly, but it was still quite audible. As with the Hafler, my reaction to this residual noise might be considered extreme since in each case I compared an active high level stage to my passive high-level stage (a volume control) which is dead silent. Also my speakers are much more efficient than Walt's Magnepans. He reports that the noise is virtually inaudible in his system. I can say that, on a relative basis, the W] 1A has more noise than the Hafler, a stock PAS or a Heath AP-1615, which were the only other preamps I had access to during my tests. At my request, Walt measured the noise level after my tests were concluded. He found a S/N ratio of 76dB on one channel and 78dB on the other, relative to 1'VRMS output, with the volume control fully attenuated. The ratios decreased by about 2dB when the volume control was set at a normal listening position. Walt says that the S/N could be easily improved but to the detriment of sound quality. Obviously, he made the right choice in pur suing better sound, and I would be the last to criticize such a decision. But if the noise 1s a problem in a particular system, one could always install a pair of 2k resistors across the output and drive the power amp from the Junction point. This would reduce all signals, including residual noise, by 6dB. Incidentally, for those readers who may be skeptical about Walt's claim that gold-plated phono jacks and a control bypass switch im prove sound quality, let me assure you that he did not exaggerate. Each of these results in a slightly cleaner and more detailed high end, as if the sound has been purified. This is not witchcraft. Ordinary phono jacks as well as slide or rotary switches are not perfect con tacts. This results in ''contact rectification" which causes an audible coarsening and veil ing of higher frequencies. To summarize, the sound of the WJ-1A is coherent, uncolored and clean. It has the virtues of the Hafler Mark I without its veiling or as much constriction of dynamics. Simply weighing its plusses and minuses, the WJ-1A is superb; its shortcomings are quibbles compared to its excellences. Nevertheless, for my tastes, it doesn't come alive quite as often as my reference tube preamp or even the Hafler, due primarily, I think, to the compression of dynamics. For some the deficiencies of the W]-1A will be insignificant or will be greatly outweighed by its superior performance in most other areas. Certainly, if you are looking primarily for a clean sound, with quick transients and a neutral tonal balance, the WJ-1A is bound to please. WJ--Walt Jung responds First I thank Dave Vorhis for a perceptive and analytical review of our design. I have no major disagreements, but would like to comment on a couple of points. I am particularly happy he found the sound to be free of colorations. We believe this particular aspect of the reproduction is due in no small measure to the absence of capacitors in the signal path, and the beefed up power supply. Dave reports the sound to be less alive or slightly compressed, compared to his tube preamp. I agree that this characteristic of the PAT-5-W J-1A's sound could be better. We have found an alternate method of operating the ICs which improves this particular parameter (dramatically so, in our opinion). Unfortunately, while the change itself is relatively simple (two resistors), it does have side effects which can upset the servo system and the DC coupling. Dave White and I are currently evaluating how to best execute this change, and to describe it so readers may reliably implement it. I consider this uncompressed character of reproduction to be a most important one, and one handled adequately by few currently available preamps. Two examples I consider to be outstanding in dynamics are the Theta Electronics unit, and the Berning TF-10, by Precedent Audio. Both of these preamps are cascode tube units (the TF-10 is a hybrid), and use local feedback only, and passive RIAA equalization. We are confident our proposed change will improve the WJ-1A's dynamics, and look forward to passing it along to TAA readers. I do have a couple of other comments to add, on references and methodology. Dave compared the WJ-1A to his cascode preamp, which is just a phono stage. But, neither I nor the readers know the details of his design. So there is really no direct way we can relate to his comments. I would suggest he share his design with us at the earliest opportunity, if possible. I'm sure most TAA readers would be interested. As to the comments on the noise of the high level stage, Dave accurately describes my (unweighted) measured results, and we did discuss this matter at some length on the phone. He also mentioned in that conversation that he uses a Williamson Twin Twenty, which I note has a gain of 30.8dB (744 1/70, p-5). My power amp has a gain of 25.7dB, open, which is much more typical. I believe the over 5dB greater sensitivity of his power amp and the relatively high efficiency of his speakers constitutes an unusual situation, and explains why he can hear noise and I can't, even with my ear in the speaker. I don't believe a 78 or 76dB S/N is a problem, unless you operate the preamp at a 0.3V or so output level when the numbers then become 68 and 66dB. If you want to add an output pad as Dave suggested, be sure to minimize your cable length. The resistors can directly replace the two resistors already used. I hope the above does not sound defensive, as I freely admit that the OC-2H op amp does in fact have a higher noise than the originally used 5534. In spite of this it was used, as Dave notes, because it simply sounds better (added to our other reasons, originally given). ------------- PROBLEMS, PROBLEMS If by some accident or other you should have some unexpected difficulty with an article some TAA author has written just sit right down and write a nice letter. Tell him (or her) very clearly and simply about the problem. If you've built something, measure everything in sight and make acute observations about how the thing is behaving. Then carefully address an envelope with your very It the author lives in England or Holland or some odd place of that sort, you shouldn't put a stamp on but send two funny things called "International Postal Coupons' which your postal clerk probably hasn't heard of but can look up in his book. Then send the whole own name, and put a stamp on it. business to our overworked but nonetheless cheerful staff at P. O. Box 176. We're disgustingly curious so we'll open it and read it before sending it to the author. You should get a reply before too long. Probably. Whatever you do don't call the office (our staff shy easily at heavy technical queries as they don't want to risk making authors jealous). Also, you mustn't beg piteously for the address or phone number of our authors. All of them are already rather more self confident than is entirely safe, so we don't want to make things worse. If your question is really entertaining, bizarre, or even informative we might use it in the magazine, along with the author's witty riposte, as a way of guiding others out of a morass similar to yours. So do keep in touch if anything takes a turn for the worse. ------------------------ Also see: The Grounded Ear--What dbx is up to with discs, PML's mike, and Sony tape The Williamson 40/40, Power Amplifier--Return of an improved favorite after a decade
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