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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
markpaul
1 posts
 

I appreciate your response. A new halogen desk light set at 1/2 on a different circuit solved my AMP5 Hum eight years later. I also noticed an annoying pulsating hum that reminds me of a lightsaber match from Star Wars once it was connected to a power source.

ianrmack
227 posts
 

I had same problem in our 120 yo house even though I have dedicated AC lines.

It's called “DC offset” and it was fixed instantly by installing an Emotiva CMX-2.
 

 

cindyment's avatar
cindyment
351 posts
 

@rakuennow 

 

Two things, one it concerns me that you are seeing such a large drop under load. Some drop is expected. That large a drop could be indicative of a poor connection somewhere or undersized wires.

DC offset on the AC line is caused by unbalanced loading on the positive and negative going sides of the AC wave. It does not happen often, but it also does not take much to cause hum. Old 2 position dimmers (popular on range hoods), 2 position motor speed controllers (some ceiling fans) may in one switch position only conduct for 1/2 a cycle. With other electronic equipment performing poorly, the conduction on one 1/2 the cycle may be lower. Result is DC offset on the AC line.

iFi, Isotek, audiolab, ATL audio, etc. make these. There is not a lot in them. Couple of capacitors and some diodes. The diodes are to ensure the voltage on the capacitors never gets very large. If it does not have a safety certification (UL, TUV, ENEC, etc.), then get one in a metal box in case there is a failure.

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