Assuming they've got BIG heatsinks on the sides, they are the monobloc versions of the old KSA 200 amplifier, which Krell came out with between their KMA 100/200 fan-cooled amps and the MDA 300/500 and KSA 150/250 amps. First came out with that generation in 1989 or so, I think (I bought one of the first KSA 80s to drive my Duntechs, and I think I got those speakers near the end of 1987). If they don't have balanced inputs, it's probably an early version of the amps, as Krell started adding the balanced inputs later in the series (at least with the stereo amps). These amps are powerhouses, and can drive almost anything out there. My recollection was that I liked the MDA 300s a little better as being sweeter in the highs, but that the KSA 80 was still a pretty good amp, particularly after you left it on for a while. Great space heaters too, as I recall the amps run Class A up to their full power output, unlike later Krells.
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It sounds like these are the ones you are talking about. The fins are HUGE and they are Class A all the way up according to the manual. They were made in 1989 but they do have the balanced inputs.
We are probably going to put these up for sale and want to learn as much as we can about them and get a sense of what they are reasonably worth. Any ideas on that? It would be ehlpful if anyone knew of any reviews of these amps that we could get a hold of--searching the web has not turned up anything.
I wouldn't know their worth (may have seen a pair of KMA 160s a while back for about $3800?), but I'll check my old S-philes for any reviews. I don't ever recall seeing a formal review of this generation of Krells in the 'Phile other than maybe in Sam Tellig columns (relating to the 80) and possible references to John Atkinson using the 400s. Perhaps our friends from across the pond recall a review in the British Hi Fi mags?
I'm the proud owner of a pair of KMA-160 monos. Their nominal 160 watt rating is conservative. They're actually in the 240 watt range, into 8 ohms. They drive my Aerial 10Ts with great authority and I've never, ever run out of power with them. It's scary to imagine what a set of 400s would do!
The 160s put out a lot of heat. 400s should be pretty awesome as space heaters. And with just the 160s drawing 7 amps each, the 400s probably should not both be plugged into the
same 15 or 20 amp circuit.
Sonically, I've never heard any grain. To my ears they're impeccably smooth, immensely powerful, and throw a huge, clearly defined soundstage with no signature sound of their own that I have ever been able to identify.
I'd love to get a set of 400s. But I'd have to upgrade the air conditioning in the room they were in.
In the MDA series of amplifiers, you would commonly find the MDA-300 and MDA-500 come up for sale... occasionally. What you would never find or maybe once in a blue, blue moon, is a pair of MDA-600s coming up for sale (only one pair has ever appeared for sale in the used market as far as we know). Being that only two pairs were ever made - One pair for Fabio and the other pair for Dan D'Agostino himself, good luck with ever finding another pair for sale. What is even rarer than the MDA-600s is this pair of MDA-400s that Dan specially built for a long time friend of his. This could be the only pair in the World (as far as we know)! And is probably even rarer than digging up a red diamond. Only the MDA-600s and this MDA-400s has the blue power output meter on its front that are similar to the uber high end KAS amplifiers. The MDA-300 and MDA-500 do not have them.
Here's someone selling the MDA-400s
Don’t believe for one minute they are 400w Class-A, having the 400 figure, they would have been conservatively rated at 400w Class A/B into 8ohms, bench tested usually a Krell will be more, like 450-500 Class-A/B. They do this on purpose (underrate) because then the true 4ohm figure looks like it doubling, to give an even better illusion of current.
As for the Class-A bias, with a rail voltage high enough to give approx 500w into 8ohms, those heatsinks then are only capable of doing 30-40w max of Class-A into 8ohms, as this amp does not have "Plateau Biasing" it’s a fixed bias amp.
If it were just a 100w amp into 8ohms (no more) then those heatsinks "may" support it biased into Class-A maybe all the way to 80-100w. But it’s not and the heat factor goes up exponentially as the rail voltage goes higher for more Class-B output.
EG: The Mark Leveinson ML2 monoblocks are just as big/heavy, and have comparable heatsinks, but are only 25w into 8ohms but it’s all class-A.