Replacing my Krell FPB 600 amp with a tube amp

Conrad Johnson Premiere 12s

Best,

Erik 

Atma-Sphere should be on your list.
B

What would be a good ARC Ref amp to bi amp with my Krell ?

Probably the ARC Ref 150? Just make sure your amps have equal gain and it really helps if you pre-amp has a variable "pre-amp out" as well as a "main out". Otherwise, you'll have to use a splitter to feed both amps.

A point to keep in mind regarding passively biamping the FPB600 with a tube amp, in addition to the gain matching concern that was mentioned, and in addition to the possible effects on coherence of driving the speaker with two very different amps, relates to the fact that in a passive biamp configuration (i.e., without an electronic crossover "ahead" of the amps) both amps must put out voltages corresponding to the full frequency range of the signal.

Your speakers have impedances in the vicinity of 4 ohms in much of the bass region. The FPB600 is rated to provide up to 1200 watts into 4 ohms. If you were to passively biamp it with say the ARC Ref 150 you would be reducing the usable power capability of the FPB600 from 1200 watts to not much more than 150 watts, because if you were to turn the volume control up high enough to utilize more of its power capability the lower powered amp would be driven into clipping.

Good luck. Regards,
-- Al