Generally, there is a small difference between FET type devices and bipolar devices. Sometimes FET devices can have a colored texture to the sound - more of a warm and fuzzy type sonic signature. This is not always the case, but FET does lean this way. The warmth of Pass Labs (and possibly Accuphase) definitely leans this way. I would not say Pass is very warm, but it’s a nice controlled easy listening sound.
Bipolar is usually a lot cleaner sounding (without that warmth influence). Gryphon is an example of this. Sometimes the high bias Class A bipolar devices can present a very smoothed over and liquidy sound (this is also an extreme coloration, but it’s different than the FET warmth). The new Krell sliding bias Class A amps are like this. New Mark Levinson are also very liquidy sounding. There are many others, but I can’t remember them.
Bipolar is usually a lot cleaner sounding (without that warmth influence). Gryphon is an example of this. Sometimes the high bias Class A bipolar devices can present a very smoothed over and liquidy sound (this is also an extreme coloration, but it’s different than the FET warmth). The new Krell sliding bias Class A amps are like this. New Mark Levinson are also very liquidy sounding. There are many others, but I can’t remember them.