Audio Research D-250 II Servo power amplifier:
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With less demanding loads, the low-end characteristic which sounds "right" (or "best," if you prefer) will be as dependent on the loudspeakers used as on the amplifier. As always, the name of the game here is mating complementary products—speakers and amps whose LF behaviour offsets one another's idiosyncrasies. I would hesitate to say that the D-250's bottom end is more or less accurate than that of other amps which seem to produce "better" bass with the speakers I have on hand, but in comparison with the average of powerful amps auditioned recently, the D-250's low end sounds rather lean—similar, in fact, to the previous version of the Jeff Rowland Design Group 7 (reviewed in Vol.9 No.1).

The matter of LF performance underscores a point I have made in these pages many times in the past: within certain limits, the sound of an amplifier depends on the sound of the loudspeakers, whose sound depends on the amplifier. Like a phonograph record, which has no sound until played by a cartridge, an amplifier has no sound until heard through a loudspeaker. And as long as the "best" loudspeakers continue to sound different, there cannot be any "best" amplifier for use with all loudspeakers. Thus, in the real world of audio, where the "best" or the "most accurate" is only that which sounds best or most accurate, the question of which is the "best" amplifier is not only moot, it is hardly even relevant.

The fact is, though, that most loudspeakers are weak through the deep-bass range, and will thus do better—at the low end, at least—with amps which deliver more punch down there than does the D-250. The Infinity RS-1B is one of the few systems not deficient through the below-40Hz range, and offers provision for adjusting bass/mid-range balance; this may be one reason Audio Research uses it at every CES for demoing their electronics. (I preferred the Threshold SA-1s on the low end of the RS-1Bs because of their somewhat better control of impact bass, but that's a personal choice.) There are, however, other systems with comparable deep-bass performance (the Snell A-IIIs for instance) which should mate equally well with the D-250.

If I needed something to pick nits about with the D-250, it would be its cooling fans. These are unusually quiet, for fans, but are definitely noisier than no fans. They produce a soft rushing noise which, while usually buried under analog-signal background noise, is clearly audible during no-signal passages from digital sources (footnote 4). It's easy enough to ignore, but it does act to raise the noise floor of digital program material. But if you're one of those people who have grown so accustomed to analog noise that digital silence sounds "spooky", you'll be a fan of the D-250. (Sorry; couldn't resist that.)

Summing Up
Where, then, would I rank the Audio Research D-250? Through the middle and upper ranges, it may well be the best amplifier money can buy. I did not have a single speaker on hand with which the D-250 did not outclass every other amplifier I've tested recently, in every area above the bass. Its low end performance is less definitive, in that some other amplifiers seemed to do better with some loudspeakers than did the D-250. Is it worth the asking price? Well, Hell, what do you want me to say? Through most of its range, it is an unqualified BEST. Through the low end, it depends on your loudspeakers. I think it's worth the money if you want the very best and have the wherewithal to pay for it. However, you can come very close to this level of sound quality for a lot less, so I don't think the D-250 is as much an unqualified winner as the SP-11 preamp, which I feel to be head-and-shoulders above the competition.

There is no question, though, that this is a rich man's amplifier—the initial purchase price is only the beginning. The amplifier is a veritable power eater, whose frequent use will have a pronounced effect on your electric bill. Then there is the cost of replacement tubes, which can easily run to a cool $1000 a year if you use the amplifier often enough. But I suppose it is reasonable to assume that anyone who can afford a $6500 power amplifier (or two) can afford to maintain it. In that way, it's something like a yacht; if you have to ask how much it costs, you probably can't afford it.

For the person who wants and can pay for the very best, the D-250 is a honey of an amplifier.

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Footnote 4: The reader should also be aware that JGH's basement in Santa Fe is a quieter listening environment than most others, one in which the noise of the D-250's is readily audible. In many environments this noise would be only barely audible.—Larry Archibald