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Getting Rid of Transformer Hum

I just picked up a Proceed AMP5 the other day. Upon hooking it up to a power cord, I noticed an annoying pulsating hum that sounds like a lightsaber match in Star Wars. This hum is coming straight from the amp, not the speakers, so it's not ground loop. There is nothing hooked up to the amp besides the power cable. What's interesting is that the amp is even though there is a standby mode, the amp was definitely turned off!

I noticed, though, that the hum got louder as the voltage from my wall dropped below 115-ish. Lowest it got to was 109 when everything was turned on, including a halogen lamp. Well, I turned off the lamp and all the lights in the house, and unplugged them -- helped the voltage drop but didn't eliminate the hum.

Am I completely lost on this amp? Or is there a way to take care of this problem without investing thousands more on some power regenerator? Another poster mentioned a similar problem solved by tightening a "chassis ground screw", but I have no idea what/where that is.

Help!
rakuennow
Post removed 
twoleftears's avatar
twoleftears
5,318 posts
 
Here's a post from Roger A. Modjeski on AudioCircle.

"One thing to keep in mind about toroids. If there is any DC on your power line the transformer will audibly buzz and the magnetizing current will go up. This is because they have no air gap. EI transformers have an unintentional air gap of about .001 inches. That's all it takes to keep a transformer happy with a volt or two on the line."

This is exactly in line with my own experience: toroidals all hum/buzz to a certain extent; amps (e.g. most tube amps) that use different styles of transformer tend not to...
tone2222
10 posts
 
I have a pair of Aragon 1Ks and one night I turned them on to hear a loud humming buzz comming from both units. I have a pair of dedicated 20 amp power lines running from the main household fusebox (one to each amp) so nothing else is on those circuits. Then I remembered my home theatre subwoofer making a similar humm/buzz when the halogen lamp in that room was set to half power - on the same cicuit as the subwoofer. So today I went across the house into the home theatre area and sure enough that same halogen light was turned on at half power, so I turned it off and the humm/buzz in my amplifiers dissappeared. Hence, even though it was across the house on a different circuit that light was still feeding DC voltage back through the main fusebox and into the dedicated lines going to my amplifiers. Hope this post helps others.
soundsbeyondspecs
132 posts
 
tone222,

Thanks ! 8 years later and your post solved my AMP5 Hum, a new  halogen desk light set at 1/2 on another circuit.

Salute ! 
rpnz's avatar
rpnz
28 posts
 
Magnetostriction. It’s usually another item in the home that will cause amp hum (not heard through the speakers)
Most common items are:
LED lights, Fan Speed controls, Some lamp dimmers, proportional temp controls on old range tops, coil heaters with thermostat fans, etc. None should be leaking DC back into the mains but they often do.

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