Well I actually have two older adcom amps and when I got them they humed like it was no ones bussiness. I found that it was due to several factors: first of all have the power cables been modified? in particular the male ends? Second are they equipped with a three or two prong male power cord, if it is a two prong that is probably your problem. Also your home wiring could cause the problem, it would be more noticeable if it is a power hungry amp ie lots of power. In my case they were GFA-565 mono blocks(300 watts @ 8 ohms) and made all of the lights in the house dim when they were turned on, heh heh heh. I assume the hum your hearing is a 60Hz ground hum all of those things could cause that hum. If you are willing to modify the amps at all (which I did) you can upgrade the gauge of all power/ground related wires and at that time add a better power cable and that should take care of all of your humming, even if your house has power wiring(which my house also has). If you upgrade everything and it still hums the amp just might not know the song you are trying to play, just kidding!! If you have any questions just let me know, I have used the amps a lot for around 3 years and they have not hummed a peep since there upgrades. Best of luck :-) TIM
