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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
tvad
9,467 posts
 
Sounds like the amp needs a new/better toroid. I seriously doubt if any power conditioner/regenerator is going to solve the problem.
radicalsteve's avatar
radicalsteve
146 posts
 
I had a similar problem couple of times. First try and lift the ground anyway - in a safe manner of course. I would suspect though that you have some bad DC on the line - try plugging the amp into a different circuit in your home. You can also try the noisehound from Blue Circle or one of the PS Audio devices to take out the DC.
rakuennow OP
81 posts
 
Tvad, do toroidal transformers usually degrade with age, or is there anything specific that would make it go bad? I doubt a high-end amp would employ a cheap toroid to begin with. If amps/toroids do regularly go bad over time (5 years?), I would be more weary making future audiogon purchases...
tvad
9,467 posts
 
05-02-08: Rakuennow
Tvad, do toroidal transformers usually degrade with age, or is there anything specific that would make it go bad? I doubt a high-end amp would employ a cheap toroid to begin with.
Like most things, there are toroids that are better (quieter) than others. The cost of an amp may have no relation to the quality of toroid installed.

I have not heard of toroids degrading with age. Voltage dipping 10% or more from a toroid's rated voltage can cause hum.

Why not have a technician check it out? Perhaps tightening the screw, or adding damping material would solve the problem. A new toroid would certainly be less expensive than a replacement amp.

Channel Islands Audio makes a power conditioner designed to eliminate or reduce transformer hum. You could give it a try.
rwwear
2,692 posts
 
An amp will hum without interconnects hooked up and speakers and power attached. Does it hum with the interconnects attached? If so, is it hum or vibration? If it is hum it may be fixable if vibration, probably not, unless the transformer has become loose. If the transformer is loose, you may be able to tighten it.

But I had a Krell amp that had a noisy transformer years ago and Krell had to send me a new amp.
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