My favorite Krells in the past have been the original KSA 50MkII, followed by the KSA 150/250, along with the KSA80/200, their predecessors. The 50, 80 and 200 are all pure Class A designs, and after warmup can sound quite nice (for solid state); the 150/250 were actually not fully pure Class A in operation, as I recall from the Stereophile review, but heavily enough biased in Class A that they too could drive just about anything out there, and they were pretty nice sounding as well, perhaps a little sweeter and warmer, if possible for a Krell, than the 80/200s. My personal favorite was the 50Mk II, which had a slight sweetness in the highs that the others did not quite match, but that's the oldest model here and used a cooling fan, which is another part that could go in the unit--the other versions have massive heat sinks. All run very hot, and can double as a space heater. After these models (and the Audio Standards), Krell went to a Sustained Plateau Bias system that kept the amp running cooler but in my view lost some of the character, and ultimate power into difficult loads, of the earlier models. The later models have their supporters too, though, as I'm sure you'll find from the answers to your post--I think it's safe to say they may be more accurate in passing the signal, but I always felt they lost a little of the music along the way. My opinion, likely not shared by many others!
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