Krell KCR-HR or Krell KAV280i

I have worked with the KRC-3 as well as the KAV-280p.

The KRC-3 has the older "D'Agostino" sound.  He tended to like a more warm sound.  It was nice, but I remember hearing some sibilance issues - could be from the warm/lush type signature.

The KRC-HR was the top of the line back then.  It has a significantly larger power supply compared to the KRC-3 line.  It also is a fully balanced/differential preamp, where the KRC-3 was only a single-ended circuit.  It was said that the "HR" was the model to go after.  It has kept its value for a very long time, even on the used market today.  I have not heard it, but I suspect it keeps the older type sonic signature but with a much more refined sound.

The KAV-280p is a completely different beast and is the "new krell" after D'Agostino left.  It also is the first generation to use all SMD devices, where the older stuff was all "through-hole" components (as D'Agostino continues to like to use).  The KAV-280p is going to be a much faster circuit that has higher resolution and more attack.  It is definitely not a forgiving preamp, but I love the sound.  It is also a fully balanced/differential circuit.  It has a fully balanced/differential input stage as well as a fully balanced/differential output stage, both fully discrete Class A circuits.

Either one of these would probably need to be re-capped because of their age.  In my opinion, the KAV-280p power supply is undersized.  The Class A circuits suck a lot of current!  I have made huge improvements in the sound quality by increasing the main power supply caps to 4 x 6800uf (use Nichicon KW).  The original caps were 4 x 3300uf if I remember right.  This provides enough power to allow the waveforms to be fully built.  This removes the brightness/harshness of the preamp and gives it much more bass strength.