To add, just idling, this amp is REALLY HOT. I'm concerned about fire potential if I leave it on 24/7. Again, any educated comments would be really appreciated. Other then their power conditioner, I'm new to Adcom.
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It is my understanding that Adcom had 3 different companies make the 555 at different times so there was considerable variation between samples. At least some of them were considered good at the time. I have never heard of them running hot. It sounds as if this sample has problems or possibily someone has set the bias very high. I would be leary of an amp running this hot that was not class a.
Adcom emailed me back. They say the heat is likely a bias adjustment issue & the differing levels of hiss could be of concern.
The person I got it from has 2 more, so I may try another, but I'm also not real thrilled with the sound. I didn't think anything could make my NHT's sound bright; I'm used to them being a bit on the dark side! Being on a budget, one of his other amps may still be a short term solution, though.
Thanks for all the replies both on & off list, much appreciated!
Abstainer, did you leave them on 24/7 (which I'd like to do)? I assume if so, you experienced no fire hazards...
The potentiasl for a fire hazard is my biggest concern. Sound quality is sadly somewhat secondary as I'm really broke right now & I suspect I'd eventually sell the Adcom if I buy it, but I'm so used to leaving all my gear on 24/7 I'm certain I'll occasionally forget to turn the Adcom off.
I still am looking into this between the pain of getting my NAD fixed & the cheap $150 price on the Adcom.
The one good thing about the Adcom is the static electricity that caused this in the first place appears to be gone.
I am the original owner of an original model GFA-555. This amp has been on 24/7 its entire life - intially with Magnepan MG2, then small JmLab, and now Paradigm Signature 8 - the heat sinks on my amp never get hot - rarely if ever even warm - checked them just now - listening at low levels they are dead cold. This has been a great amp for me - maybe I just got a good one but I have always been very satisfied with the sound and performance of this amp. YMMV -
Moo, I've had a mkII for about 15 years without any problems whatsoever. When it was my only system I ran it 24/7. At idle it runs just slightly above room temp, but the longer/louder you push it the hotter it gets. Never really gets too hot to touch though. I recommend leaving it on 24/7 if possible for best sound. I use it sparingly lately and turn it off/on as needed - big difference in sound quality IMO. Not the smoothest amp around I'll admit but sounds very good with speakers that are voiced a bit on the warm side like my VA Bach Grands. Pushes them to the limit with great control. Probably not a great match for NHT which, from what I've ever heard, are a bit on the bright side.
Bottom line: still a great amp for the money though if the heat does bother you get it checked out.
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.
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.