Replacing my Krell FPB 600 amp with a tube amp

aoliviero..... I just read your review and i really did like what i read about it. Especially compared to the Krell FPB 600. Wonder how it compared to the ARC Ref 750se. 

I went up the Krell line of amplifiers in the 1990s, and ended with a FPB 600, which deserves high praise, but has certain - let me say - conditions. In my system, it sounded much better when it 1) got a dedicated power line, 2) a solid slab of stone below, 3) a good tube preamp rather than a mid-line Krell or other solid state (the manual warns of possible problems with a tube preamp, a jumper can be used, but I noticed much better sound without it, and never had problems), 4) using balanced inputs, and 5) matching speakers. The ones I had (Dynaudio Consequence) were a bit too much even for the 600. So the sound went from good to marvellous only on a quite high volume level (the amp shifting into class A operation). Even this power beast could not really unsettle the rather Germanic Dynaudios and make them sing and dance. Experimenting a little with speakers, I marvelled at how good the amp could sound driving an easier load. Since it was not possible to add another 600 amp to my setup, I ended selling both the amp and the Dynaudios, and bought Atma-sphere MA-1s instead.

I could say "I have never looked back", which is mostly true, but having lived with the Krell for ten years I have a lot of respect for it, it is a classic in some ways, and I have often wondered if there was even more potential to it than I managed to exploit in my setup. It is a bit of a paradox, the FPB 600 was sort of a "solve-all" when it came, it should not matter what speakers you gave it, it ate them all, and so on - but my experience was different, this amp is so good that everything you do - in terms of speaker matching, and the points mentioned above - is well worth it. Just before I sold it I had the Krell drive my small Aurum Cantus 3 speakers to great heights. 

This was some years ago, but I remember thinking: connecting a 1k dollar set of speakers (the Aurums) to a 12k amp cannot be any good. So I was surprised.

I often wondered if I would prefer a different bias system on the Krell - an option to make it go into class A operation on a lower volume level, or more user-controlled. Maybe it came in a later version (mine was a 1997 first version).

Note: my version of the amp does not make it clear when it shifts into class A; the nearest I could get was to feel the heat on the top plate. As soon as I turned the volume up with the Dynaudio speakers, the top plate turned hot, playing loud, very hot. So it may be that the amp was already working in class A, no problem there, but it was striving with my over-controlled speakers, which would have liked double power - 600 watts per channel (I never got a chance to try this).

I heard an interesting transformation of B&W 801 Matrix S3 speakers driven by Pass Aleph 1.2 mono blocks (200W/Ch).  They became smooth and rich even in the treble, which before had always had a bit of harshness to them.  So budget permitting if it were me, I would consider a Pass XA amp to replace the Krells. Rowland amps are also "tube-like" although rare on the used market.  I am also not sure that your speakers really need 600W to begin with.  One caveat- I agree with Mr. Holter that the Krell FPB's are very good amps- I had one myself and it was a joy to use- reliable, quiet, unflappable, easy on the eyes, etc.