Solid State Preamp Reviews

Editor: I think you are correct in stating that, for the most part, the Audio Research preamp and Thaedra are different yet equally rewarding. The ARC is superb and, having held its high reputation for such a long time, has been a very stiff competitor.

As you pointed out, Thaedra is sonically better in some ways, especially in the low frequencies (due to the servo) and in the highs where it exhibits more airiness (due to its wider bandwidth). These are the areas which provide a great sense of impact—particularly the lows. I believe I can add more insight into the sources of the other sonic differences noted, but first, I would like to comment on some of the features you failed to mention and which I feel deserve consideration.

The low-frequency filter was designed to remove rumble that is present on a great many recordings and would otherwise cause IM distortion and wastage of amplifier power (better utilized for the musical information). It was decided that this filter must be passive so as not to add any coloration. Without it, the response of the entire preamp is flat to below 1Hz.

The construction quality is superior to other audio gear. (For example, all internal plug-in pins and sockets are gold-plated.) The quality of the parts used is at least equal to that of the Mark Levinson equipment—sorry about that, Mark!—although there are more of them at lower cost. (Incidentally, the JC-2 is also a superb sounding preamp!)

Thaedra provides full monitoring and copying for up to three tape machines, whereas as the ARC does not. In addition, the crosstalk between any two inputs is at least –120dB from 20Hz to 20kHz when properly terminated. Since the output impedance (actual, not "source") is 60 ohms, Thaedra can drive directly virtually any low-impedance headphones such as the Koss PRO-4AA and the Yamaha HP-1.

Thaedra is the only preamp in the world with totally separate, optimized preamp boards for conventional magnetic cartridges and low-output moving-coil types. Knowing that you are going to say that features have nothing to do with sound quality, I feel there are audiophiles who do desire features.

Now to your other nitpicks. As far as looks are concerned, beauty is in the eye of the beholder (although at this price I would certainly not use plastic knobs!). You are correct in reporting that the volume control has 2dB steps, but I do not find 2dB steps to be bothersome. But then, nothing's perfect, is it?

I am glad you noticed the tracking accuracy of the volume switch; it is not a potentiometer with detents, but rather an honest-to-goodness multi-position switch with individual precision metal-film resistors between steps. You missed one of our strong points, though: If you had checked the 20kHz squarewave response through the high-level inputs, you would have found absolutely no rolloffs or other aberrations at any setting of the level control. The same applies to the tone controls. Since they are exactly the same type of control as the level control, they are effectively out of the circuit in the Flat position. This eliminates the need for a tone cancel switch. Since the tone-control switches are in the feedback loop of the high-level amplifier, there are no additional stages serving only the tone-control functions, as there are in most other preamps (including the ARC).

To suggest that Thaedra is unique in having many class-A stages, some of which run very hot, is incorrect. All preamps operate in the class-A mode (with the exception of those using ICs, most of which have class-B output stages). The difference is in the class-A power level. There are 4 independent power-supply regulators which dissipate approximately 12 watts. In addition, the line amp for each channel operates at a quiescent level of approximately 4 watts. So Thaedra does indeed run warm.

One of the last points I would like to make is one that I feel is of extreme importance even though somewhat ambiguous. The noise level on phono is 7 times(!)—that is, 17dB—lower than that of the ARC, I am surprised that you did not comment on this as you must surely have noticed. This unfortunately can sometimes be a mixed blessing. It has been shown in the past that when an "inaudible" noise field is mixed in with the signal, a quality of ambience is added to the sound, giving it a false impression of (for want of a better word) "lushness." When this masking noise field is removed, imperfections in the tape and discs become more apparent and consequently more objectionable. This might explain why the ARC supposedly sometimes sounds more musical although it is not as accurate. I have observed this effect myself, but I do not consider it important enough for me to give up accuracy. One must decide for himself which is the lesser of the two evils. I know how you feel about commercial recordings, about which I feel the same.

Finally, I am glad to see that you find some merit with moving-coil cartridges. If I did not feel they were worth it, I would not have gone to as much time and effort to design the head amp, which is specifically optimized for moving-coil cartridges. As you pointed out, the head amp is its own phono preamp stage. The JC-2 uses a combination of the JC-1 pre-pre-amp in tandem with the regular phono preamp in order to accommodate moving coils. I am convinced of the superiority of the moving-coil principle, and I do hope you will evaluate the EMT again, this time through Thaedra. Although it is very expensive ($330) and hard to obtain, it is the very finest cartridge available. Incidentally, it has a spherical stylus.

The retail price of Thaedra is $899 West Coast and $909 East Coast and, who knows, maybe soon it will be a bargain.—James Bongiorno, President, Great American Sound Co.