It could be a number of things, but two that I think of immediately are the power electrolytics (capacitors) or the rectifier. Both smooth out 60 Hz from the wall and could be the culprit. This is an easy fix.
11 responses Add your response
Thanks so much for the responses:
@mental That seems like a very easy fix- will certainly try that first. Do you run through a power strip or GFI of some sort? Not sure if that would make the amp more susceptible to surges or other fluctuations.
@stevecham I will try googling those terms as I am electrically illiterate. When you say 'This is an easy fix' do you mean replacing those components?
@mental I have an extension chord that accepts three prong cords but is itself ungrounded/two prong. I ran the receiver through this with no audible change in the hum.
Not sure if this means anything but the speaker hum is audible once I switch on power at the rear of the amp (is this sending current to the transformer?) and gets very minutely louder when I turn off the standby mode it immediately powers into. More power = more hum? Also, now that its quieter in my space I can convey that the hum is most noticeable at a distance of between 3 and 6 inches but is still easily perceptible at 12", significantly less at 24", and inaudible at 36". Grateful for any other thoughts.
often the hum is caused by a transformer which has loosened and starts vibrating--i've cured it by opening the chassis and screwing down the transformer (make sure you keep the unit unplugged for a day or so before you do so). if it's some sort of group loop, you can also try a group isolator, which is a plug that goes between the ac receptacle and the power cord
my guess is that if it's audible within the chassis that it's more likely a problem with the internals of the unit itself (loose transformer, failing power supply, caps, etc.) than with the ground or power, but it could be a number of things. i certainly don't see any harm in tightening the torroidal transformer before moving onto other causes. be careful
@loomisjohnson Sorry, meant to say that the hum is not coming from the chassis, but the speakers only. Will leave unplugged and see about taking apart tomorrow.
@stringreen Unfortunately I am not the original owner and can't imagine that the unit is covered under warranty. Having the hardest time getting in touch with Simaudio anyway...