a new amp hum problem...checked the archives

Recently, I purchased a new amp. It hums. Not just the speakers, the amp itself. The only thing I haven't done is open the amp and tighten the screws. Here's what I have already checked out -

Disconnected everything from wall except amp, then disconected everything from amp except speakers. So the only players are the wall, the amp, and the speakers. Tried a cheater plug - no help. The amp still hums and the speakers still hiss. I've plugged the amp into different outlets on different circuits - still hums.

I have noticed that the hum and hiss seem to cycle a bit - it appears to get louder and softer, but I may just be crazy. I love the sound of the amp, but can't live eith the hum. If it's an electric problem, why doesn't it affect anything else? Didn't affect my receiver (which is now a preamp). I have a HSU Research amp for my subwoofer that used to hum, but (I know, I know...) a cheater plug solved that problem. I don't know what to do.

I am very frustrated and need your help.


If the hum eminates from the chassis and not from the speakers then it's quite likely that the amp has a noisy transformer. You'll want to check with the manufacturer to see about getting an amp with a quiet transformer. There's nothing you can do (cheaters, screwdrivers, etc.) that will help quiet a noisy transformer.

If the transformer is not undersized, then tranny noise is usually the result of incomplete vacuum impregnation (sucking epoxy varnish or the like into the transformer under a vacuum to glue all the wires and magnetic bits together into one solid mass) and simply replacing the tranny with another one will take care of the problem. If the transformer is underdesigned -- too small for the job, running at too high a flux density -- then it's gonna be noisy no matter how thoroughly it's been impregnated.

Contact the manufacturer -- they should be able to sort this out pretty quickly.
I've read of a transformer mechanical hum issue due to external influences - namely lamp dimmer interferences - anywhere in the house. One other situation involved an electrically noisy vent fan that somehow excited the transformer laminations into a loud hum.
It may be possible to clamp down on the noisy transformer by adding some long bolts with large washers, effecting a "squeeze". Check to see if there are any available bolt holes? A long hose clamp wrapped tightly around might also work. Also check the mounting hardware for tightness & possibly add some rubber or sorbothane washers or footers. If in warranty then insist on a replacement xfmr. If this is a Belles amp then this is not an unusual scenario.
A bad, leaky or not screwed in tightly capacitors can also generate hum from an amp (alone) through speakers. In my instance, the hum was a constant one. After replacing the capacitor the hum went away...

Good luck!
Did you try plugging the amp in somewhere other than your home? I have found that most "hum" is generated by something in the home. It could be almost anything. I had the same problem with my amp. I thought that the low hiss was from the circuitry in the amp. I also had hum that would come and go. I narrowed the source down by turning off the branch circuits in the electricl panel until it went away. Turns out the problem was in my air handler. A bad solid state relay was to blame. I also had a customer call me with a hum problem that was coming in over his baby monitor. It was so bad that he could not sleep. I told him to try to narrow the source down by turning off circuits. No luck, so I told him to buy a recepticle tester and check all of his outlets for correct wiring. That was the ticket, he had one that was not grounded and one with hot and neutral reversed. After correcting these things the hum was gone. He also remarked that his favorite radio station came in a lot better too. You may have guessed that I do this type of thing quite often. I can solve most people problems over the phone. If you plug the amp in somewhere else and it does not hum then you know that something other than the amp is to blame. If you turn circuits off and it goes away, you'll be a step closer to getting rid of the problem. call a qualified electrican, at this point, to check things further. Hum really sucks, but 99% of the time it is not the equipment!
Really works. Search on audio asylum for more details.
thanks for the suggetions -

today, i purchased a line conditioner which failed to alleviate the problem. it wil be returned asap.

also, i did open the amp to check the transformer, but it seemed very securely fastened. i'll give it another look.

it's a huge transformer. there's already a bolt through the middle, but the washers aren't very big. i have some left over foam rubber circles with matching washers from my salamander archetype rack - maybe i'll try clamping down with those. also, i checked with the manufacturer - he'll replace the trans, upgrade the caps, and give me a 20 year warranty on the amp, but that's $400 i don't have...

as for the capacitors, i guess i can check those - do they just 'push' in?

i haven't cut the other circuits in the house yet, but i guess that's an option. i am also planning on trying the amp at a friend's house to make sure that it is an internal problem and not an environmental one. i will also research the Ah Offset Killer.

thanks again, i'll keep you posted.
here's the next question. i decided to further tighten the transformer to the chassis and the hum has diminished significantly, but not completely. the question now is how tight can you make it? if i tighten it anymore, i am worried i may damage the transformer. any guidelines on this?

I had a similar problem with an amp. As it broke in the hum disappeared. Maybe you should just let it break in like I did which is a very simple solution and see if that helps.
anyone know about the ah! ac offset killer? how it works? a less expensive alternative? still can't kill the hum.