The hum from the front of the amp IS from the power xfrmr. It's probably a result of DC on your incoming power. It is almost certainly not a ground loop. As far as how hot the amp runs normally, that depends on a lot of things, including how far into CLASS A the amp is biased. Also, while the nominal spec on the 683 is 8 ohms, there are some reports on the web that they dip to 3 ohms within the audioband. The Adcom's published power specs show that while the amp is rated for a 4 ohm load, the power output does not "double down" and the rating is for continuous average power, not RMS. both of these factors lead me to believe that the amp is not fully capable of driving low impedance loads and that may be why the amp is heating up. Or it could be normal, or it could be that it needs repair. Maybe some of our more tech savy members can say if the DC leakage could cause it to run hot.
Hum inside adcom amp and hiss at tweeter
I just bought a used adcom 5503 and noticed it has a hum inside the front of the amp. I think it's the toroid making the noise. Up untill this amp there have been no noise or hiss of any kind from my system. I have a marantz sr7005 as a preamp and have an adcom 555 that I was using until I got the 5503 and it was silent. Also had some marantz ma500 that were silent. The 1 thing I noticed was the buzzing is altered when I power on and off my receiver. Does that mean it is dirty power? Also the amp seems to run super hot. I measured it at 125 deg f at the heat sinks. Does this seem to hot for low level listening? It does take a while to get that hot like 2+ hours. What I was going to try was the cheater plug without the ground and see if maybe I have a ground loop. My speakers are b&w 683 and are 8 ohm so the load is not that bad for the amp. Thanks for any advise. Mike