Audio Research SP-3 preamplifier

Preview, from Vol.3 No.3: We thought Audio Research's previous-model SP-2C (footnote 1) was excellent, but this is even better—the closest thing available, in fact, to the ideal straight wire with gain. Our sample had a minor glitch—there was a slight "plop" if you rotated the tone controls rapidly—but we could find nothing else about it to criticize. Currently, by far the best preamplifier than money can buy. And would you believe it uses tubes (at reduced heater voltage, for extended life and cooler operation)!

Price is a most respectable $595.

J. Gordon Holt wrote again about the SP-3 in Summer/Autumn 1973 (Vol.3 No.5):

We have been watching with fascination the announcements for what looks like a new breed of preamplifier (as typified by the Phase Linear), equipped with sophisticated circuitry for reducing noise and expanding dynamic range, and whose manufacturers make a point of the fact that they are not straight- wires-with-gain. We are fascinated because we are just dying to see what these preamps can do with program material that is noisy and compressed. We are also curious to hear what they can do with program material that is quiet and uncompressed—the kind that is, that calls for a preamp that is a straight wire with gain.

Meanwhile, we will continue to be completely happy with the closest thing we have found to that ideal straight-wire-with-gain—the SP-3 from the Audio Research Corporation.

There is really little more that can be said about the SP-3's sound. Quite simply, it modifies the input signal less than any other preamp that is currently available (with the tone controls out, that is), and what change it does effect.—an extremely subtle softening of "hard" transients is of a kind that the ear finds much more agreeable than the typical solid-state hardness (which exaggerates the hardness of commercial recordings) or the typical vacuum-tube haziness.

We mentioned that there is some degradation of the sound passing through an SP-3. We should qualify that by stating that the unit is equipped with a tone-control bypass switch (actually, the controls are normally out of circuit; the switch puts them into operation), and that the sound is just a hair cleaner with the controls out. With them in, the difference between the sound coming out of the SP-3 and the same sound directly to the power amplifier, bypassing the preamp, is so slight that, even with the very best associated equipment, it takes a sophisticated ear to detect any difference at all. And it is precisely that kind of ear that will appreciate the superiority of the SP3 over any other preamp.

Most perfectionists have noticed by now that the earliest stages in a system seem to be the most crucial as far as distortion is concerned. A very small amount of distortion that would be virtually undetectable in the latter stages of a power amplifier seems to add entirely disproportionate amounts of hardness and edge to string tone and mis-tracking distortion when it originates in the preamp stages. We don't know just how low the distortion is in the SP-3's preamp (it was unmeasurable on our modest little Heath Audio Analyzer), but it sounds lower than in any other preamp we have ever heard, if cleanness and musical purity are any indication, which they are. There is less of the things which generally annoy us in phono reproduction, but virtually none of the dulling or softening that has characterized the sound of other preamps that don't exaggerate breakup or steeliness.

You may not like the sound of your system with the SP-3 in it, for you may want or your system may need some extra hardness to cover up the fact that your speakers have lousy transient response, and it's your God-given right to be wrong about such matters. But if you want the best-sounding preamplifier that money can buy, and have the money to buy it, the SP-3 is unquestionably It. (Two designers of new preamplifiers have told us recently that theirs sound "as good as the SP-3." Maybe they do, maybe they don't, but when the competition admits that a product is the standard by which they judge their own efforts, it says something for that product.)

Since the SP-3 uses tubes instead of transistors, there is of course the possibility of tube-type problems and the certainty, at some future time, of the need for tube replacements. Audiophiles who have owned only solid-state gear may be introduced to microphonics and other-worldly binging or boinging noise that a rare tube will inject into the system when the preamp is jarred. Since all the tubes in the SP-3 are identical (12AX7 types), it is a simple matter, when microphony is encountered, to locate the bad tube (by gently tapping each one in turn with the fingernail) and swap it for one of the others.

The old bugaboo of creeping distortion—which sneaks insidiously up on you as the tubes start to wear out, and which transistors were supposed to eliminate (some of them do the same thing but for different reasons) is of course a consideration with the SP-3, but a small one. There will come a time when tubes will have to be replaced, and there are eight of them in the SP-3. This should not be cause for alarm, though, for the tubes are operated at below-normal heater voltage and power dissipation, which means they will last several times longer than normal. ARC indicates that five years "under normal-use conditions of several hours per day" is not an unreasonable expectation, but we should add that the 12AX7s in our ancient Dyna PAM-1 preamp (operated under similar power-supply and use conditions) racked up nine years before starting to sound sour.

Footnote 1: Of the SP-2C, J. Gordon Holt wrote in Summer 1971 (Vol.3 No.1), Unquestionably the finest-sounding preamplifier we have tested to date, this [high-priced ($550) and all-tubed preamp] is the next best thing to the ideal "straight wire with gain." Sound is extremely lucid and detailed, but without a trace of the hardness or graininess that characterizes most other preamps. Control and switching facilities less versatile than on some competitively priced preamps. Phono equalization accurate to within 0.5dB.
Audio Research
3900 Annapolis Lane North
Plymouth, MN 55447-5447
(763) 577-9700