mobanmarket Our first sample of this preamplifier was returned to the manufacturer before we had completed our tests on it, and was replaced with the latest version (ours is serial number 500108). Enough time elapsed between the time we shipped back the first sample and the time we got around to auditioning the second that we are unable to report on any sonic differences between the two. We are prepared to report that the present one, designed by James Bongiorno (footnote 1), is the most deeply satisfying of any solid-state preamplifier we have tried to date (as of May 22. 1976, footnote 2).
Admittedly, it is not the virtuoso of versatility that is, for example, the Yamaha C-l (which can do practically anything short of dispensing draft beer), and it is not one of the prettier preamps—striking but hardly pretty! But it does all the things that one normally expects a preamp/control unit to do, and does them in exemplary fashion.
For example, most serious audiophiles now recognize that one of the worst drawbacks of the currently popular (we are tempted to say “faddish,” but we won’t) moving-coil cartridges is that they require a bootstrap input booster of some kind in order to drive adequately a standard phono-cartridge preamp stage, which means either a transformer (which introduces harmonic, phase, and frequency distortion) or an outrigger “head amplifier” in that part of the system where distortion is most conspicuously audible: Ahead of the phono stage. The fact that some other recent preamp designs have included a built-in head amp does not change the fact that there is still that additional stage of amplification—and of distortion, no matter how slight—ahead of the regular phono preamp stage. Well, GAS does it differently.
Thaedra has a “head amp” input, but instead of being located ahead of the main phono preamp section, it is itself a completely separate extra-high-gain phono preamp. Under the circumstances, it was not too much of a surprise to us to find that every moving-coil cartridge we tried with Thaedra sounded better in every respect than it ever has before. (The fact that an optimized Shure V15-III spherical can sound as good as any high priced moving coil we have tested will probably not impress readers who are already convinced that moving coils are the only way to go.)
We don’t normally comment on volume control tracking unless it is unusually good or bad. We comment here because it was better than any we have encountered to date: Tracking error (channel difference) was less than 0.5dB over the entire operating range of the control! The only preamp we have encountered that had comparable tracking was the Yamaha C-l, reported elsewhere in this issue.
Sound Quality
Sonically, we found Thaedra difficult to fault. What came out of it was a virtual replica of what went in, and the only imperfections we were able to observe—a subtle richening of the sound, an exceedingly subtle grayness, and a very slight loss of depth and inner detail (in comparison with no preamp at all)—were all in the nature of deficiencies rather than exaggerations and were thus found to be very easy to live with. It surpasses—not markedly but quite perceptibly—the Audio Research SP3A-1 in every aspect of performance except inner detail, depth and liquidity. (That liquidity or crystalline transparency that we observe in the better tube stuff has been attributed by some to a consonant form of distortion (footnote 3). We say “Nay” to this, for it is present to the same degree when there is no preamp in circuit at all.)
Our only complaints about Thaedra are in the nature of quibbles. The stepped volume control changes the level in what sound like 2dB steps through its most-often used rotational range (12 to 3 o’clock). And although 2dB is really a very small level change when it occurs across the spectrum (a change of 0.5dB in frequency response can sometimes be perceptible), there is a certain perversity of human nature—our human nature, at least—that made us wish at times that we could adjust to a spot precisely midway between two available settings. If this is suggestive of a mild neurotic compulsion of sorts, then so be it; nobody ever pretended that audiophiles are normal.
Secondly, there is no provision for switching out or bypassing the tone controls, which provision may or may not have improved the sound perceptibly. And finally, high-level-input impedance (around 40k ohms) is low enough that it could cause some distortion Olid low-end thinning from certain tuners and taps recorders. For example, no tubed components we know of were designed for that low a load, but since tube-type tuners and tape machines are already on the verge of becoming museum pieces, we don’t really feel that to be a serious consideration.
Readers considering the purchase of Thaedra should be forewarned that, because many of its transistors are class-A-operated, it is normal for it to get quite hot after an hour or so of use. Just make sure it is installed where there is an unobstructed flow of air to the bottom panel and from the center of the top panel.
Since this is priced as direct competition for the Audio Research preamp, it has to be directly compared with it, and the fact is that (as often the case) there is no winner and no loser. Thaedra has tighter, deeper low end—what’s the matter with the SP3A-l’s low end, anyway?—crisper attacks on sharp transients (hard percussion, etc.), an impression of somewhat more high-end airiness, and controls that are—but for the volume-control thing mentioned previously—a tactile and functional pleasure to use. Plus, of course, that superb head amp, for moving-coil freaks. The ARC is still not quite equaled for liquidity, depth, and inner detail in complex program material such as full orchestral tutti and massive choral passages. To us, the ARC also persists in having a degree of musicality—an intangible “rightness’ in the reproduction of acoustical musical instruments (which are still the sole valid criterion for fidelity)—that no other preamp we have yet encountered (or have heard of) can match.
Summing Up
Our advice: If you don’t get to hear live acoustical instruments more than a few times a year, you will probably prefer the sound of Thaedra. If on the other hand most hi-fi reproduction you hear sounds more or less dry or astringent to you, you’ll almost certainly prefer the Audio Research.
We’ll add one observation in closing: Everyone has known that, eventually, someone would design a solid-state preamplifier that would at least equal, if not surpass, the ARC. This one, we feel, is its equal, although rather in the manner of Macintosh apples versus Winesap apples. Whichever you feel to be the best is purely personal, and we don’t think you would like The Apple-Eater’s Guide to tell you which you should prefer. So we won’t.
Footnote 1: James Bongiorno passed away in 2013 after a long illness.—John Atkinson
Footnote 2: We should add that, as of June 25, 1976, after having auditioned all the other preamps covered in this issue I still feel the same way.—J. Gordon Holt
Footnote 3: The opposite of dissonant.—J. Gordon Holt