ADCOM

I owned a GFA-555 for 30+ years.
I worked as good for all those years until I sold it a year ago.
Nelson Pass did a great job on those amps.
I have no experience with other Adcom equipment, but suspect it to be equally good.
Bob

I own a 545v2, also a Nelson Pass.. sounds pretty good.. especially for about $250.. I keep as a back up for when my main amp is being switched or fixed.. I never feel I'm missing that much when in use.. My main amps float n the $6000- $8000 range new

Gfp750 preamp and gfa565 mono power amp.

I've owned various Adcom items and they were always nice sounding and reliable...I went for the tuner-preamp with a 535 when they first came out, later a balanced preamp (can't remember which one) used with different power amps, and more 535s (used and new, including the 535II) both for studio and otherwise. Sold 'em all eventually except a 5300 that's used for remote (deck) speaker duties...that amp sounds great and was seriously inexpensive used. Nice stuff, but watch for oldness issues...leaking caps, hair loss...

In the past I've used a GFA5802 to drive Martin Logan Ascent ES hybrids. All MosFet heavy bias AB amp. A fair amount of heat but no fans. I had to go to a Pass X350 to upgrade. The Adcom is still on active duty driving a pair of JBL 4430s.

It's a pretty good amp for the money.