Adcom 555 Mk 2 Questions

FYI, it turned out the amp was bad. Hissing kept getting louder, then it died.

The person who I got it from had another. So far this one is running much cooler, with no audible hiss. I'm still not thrilled with the sound (though it may need to break in, I don't believe it's been used in several years). If it continues to be stable I think I'll buy it ($150) & continue to look for a repair option on my cheaper but better sounding NAD 2600. If I ever get the NAD repaired, I should be able to sell the Adcom at a small profit.

To clarify, it's definitely not ice cold like Kencrouch reported, but so far it's warm rather then hot.

I'm also running it on top of a cabinet rather then inside as i normally do (though inside is very well ventilated.).

Has anyone run these amps in mono mode? How did they sound?

I have a old 555 and I think it is a MkII because the RCA inputs are wide apart, not right next to each other as I see the originals are.
It has excellent sound. Not bright at all like some of the folks above speak of. I have it taking signals from a Dynaco Pass and feeding Acoustat 2s. This is great symmetry. The warmish Pas preamp and the big SS Adcom make beautiful music together.
I am interested in modding to some degree. First up will be cutting a hole in the chassis and installing a IEC plug socket. Afterwards the input board caps.
I don't see much to do to the power supply,since it is quite huge. This thing looks like a big empty box with one smallish board, a big toroidal and 4 big power caps.
Any mod info would be helpful.

e

I used an adaptation from an old Audio Amateur article to build a fully regulated power supply and it made a big difference in the sound quality especially with dynamic swings.

Kal

Hi, I know this thread has been going on for ages now. My opinion for the GFA-555 is a powerful and very quiet amplifier. Those who say it gets hot ,well there must be something wrong w/ it because mine does not even get warm under a heavy load. For the price used mine was $300 from Audio Classics sight and sound unseen just on reputation (SHIPPING THROWN IN ) and it came slippery clean and work the 2nd I hooked it up. I know tubes take time and I don't have the patience or that so I went ss and it's really instant on and does not get better the more you play.Yes when you shut it own and it spools down i does take a few minutes but who cares, your done listening. I sometimes leave the amp on all the time and I'm torn about this because most the people over on the POLK site swear by it and I must be a hypocric because  I have a sub woofer that has never been off since I got it about 9 y/o. For durability, price point ,looks, and form and function one could not  do much better.  For a starter amp or even your go to amp I would not hestate and go for it. My model is a bit different ,I have the rack face model used for recording studios because of their power and low noise floor. Highly recommended  for a step into 2 chll genre....Some say it's a bright sounding amp. I have no way o comparare and would like a Parasound or Bryston to get and hear the difference....Lew