Krell KSA-50 power amplifier
The timbre of this amp is sufficiently neutral and uncolored that there just isn't much to say about bass, midrange, and treble. They will tend to reflect the input signal and interconnects rather than the amplifier. I can say that you will want to use interconnects like the Straight Wire, Distech, and Randall rather than the Monster and MIT, and that the amp seems to work best with a dynamic cartridge possessing a slightly live midrange, like the Koetsu Black Gold or the Kiseki Purple. This, however, brings me to the sound qualities of the Krell KSA-50 that are truly unique.
Like most of the better class-A amplifiers I've heard, the Krell KSA-50 sounds liquid rather than dynamic. While no two class-A amplifiers ever sound alike, they all share a kind of mid-hall sound. Rather than give you "exciting" sound with a great deal of "forward" dynamic energy, they seem rather to disappear into the music. The Krell does this more than any class-A amplifier I've heard. I suspect this is because of the Krell's ability to deliver strong bass into virtually any speaker load, something for which most class-A amps lack the power, and because the designer (Dan D'Agostino) has gone to great pains to remove the last trace of hardness from the upper octaves.
In any case, the KSA-50 can resolve all the detail from the music without imposing itself. I would personally prefer a slightly more open sound, and slightly faster handling of transients, but this is quibbling.
The Krell also impresses in terms of its noise floor. As audio electronics continually improve, it becomes ever more apparent that a great deal more "trace" or low-level noise is audible than was previously thought possible. The Krell KSA-50 produces an amazingly low amount of such noise. In fact, the amplifier's only sound is the mechanical sound made once it is turn ed on, and that is virtually inaudible. This kind of quieting will not be apparent at the dealer's, but makes quite a difference during those late-night listening sessions when the room is really quiet.
The Krell also provides outstanding performance during passages of extremely soft music, or when you want to hear very low-level musical information along with medium- to high-level information. The KSA-50 is one of only a very few transistor power amplifiers that approach tube units in their ability to accurately reproduce low level music.
This is not a high-power amplifier, of course, and is more suited to speakers like the Quad ESL-63, Thiels, and Vandersteens than to the big power gobblers. It can, however, reach far into the deep bass, and proved able to drive subwoofers like the RH Labs with considerably more true deep bass than some amplifiers rated at well over 100 watts. This may be the result of the KSA-50's amazing load tolerance. This is the amplifier for truly difficult loads.
The KSA-50 is beautifully styled and built. I have never seen any piece of audio gear built quite so solidly, or, when the cover is removed, assembled with such ob vious care. This is Rolls-Royce quality of a kind few competitors are likely to equal.
The Krell does, however, carry a Rolls-Royce price-tag (at least for an amp of its power rating): $1900. This brings us back to the little matter of taste. The KSA-50 is a superb amplifier, but is it really any better than the Audio Research D-70, or a wide range of other high-quality amplifiers? I can't answer this question for you, only identify the salient tendencies and point you in the right direction. There is no substitute for your own ears listening to these excellent amplifiers in your own system. A dealer or reviewer can hype a product, but its no substitute for your audition. Ultimately, audio is a participatory, not a spectator, sport.—Anthony H. Cordesman
John Atkinson compared the KSA-50 with the KSA-50S in August 1995 (Vol.18. No.8):
I reviewed the original KSA-50 for the August 1983 issue of English magazine Hi-Fi News & Record Review, where I was very favorably impressed by its sound quality, enough so to purchase the review sample, which I brought with me when I moved to the US. The earlier KSA-50 has only unbalanced inputs, so for the comparisons with the KSA-50S, I hooked it up with 10' lengths of unbalanced AudioTruth Lapis fitted with RCA jacks. The '50S was auditioned in balanced mode so I wouldn't have to plug and unplug RCA connections, with all the potential for blowing up speakers and amps that that entails—hey, I own the B&W Silver Signatures and one of the amplifiers, okay? The balanced 'S was 3.8dB more sensitive than the unbalanced '50; again, levels were matched to well within 0.01dB at 1kHz.
Listening to the original '50, which I haven't fired up in almost six years, brought the memories flooding back. The soundstage was wicked big; the bass was wicked deep; the amp was wicked GOOD! In the "Christe Eleison," from the Mozart C-Minor Mass's "Kyrie" (Peter Schreier, Dresden Staatskapelle, Philips 426 273-2), Barbara Hendricks soars to a glorious climax. The old Krell allowed me to hear her voice lighting up the surrounding acoustic in a delightfully unambiguous way. And in the opening of the "Kyrie," the pulse of the dotted rhythm pushed the pace along.
The new Krell was significantly better than its predecessor in one important way: that gloriously liquid quality I noted earlier made the earlier Krell sound a little "electronic" by comparison. Hendricks' voice acquired a rather phlegmy edge via the older amplifier; the '50S presented it with a significantly more natural character. The original KSA-50's high frequencies were also grainier compared with the KSA-50S, and slightly sibilant. The new amplifier had altogether a more civilized, more neutral sound, I found. But when it came to the soundstage, the Dresden walls weren't illuminated to the same extent as they had been with the old amp.
And the new amp lost something of the sense of pace. It wasn't that it couldn't boogie at all, but when it did so, it was definitely in a more mannered way. Despite the more natural, less grainy presentation of the vocal, the combination of bass guitar and kickdrum on "Tell Everybody I Know," from the killer Keb' Mo' album (Okeh/Epic EK 57863), for example, could officially be classified as "polite" through the '50S. Perhaps as Krell designer Dan D'Agostino and the rest of us baby boomers get older, so does the sonic character of Krell amplifiers keep pace with our shifting desires.
While the Krell KSA-50S's bass is not quite as awesomely kick-ass deep as the earlier KSA-50, it has lost some of the slam, the "Wham, Bam, thank you, Dan!," that characterized the original KSA-50.—John Atkinson