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Belles amp hum ... rf problem?

Hi all. I have a noticeable hum problem which I have isolated as coming from my power amp, Belles 150a hotrod. The amp hums when I have it plugged into the wall with nothing else attached. The hum is not always present. I'll go a couple days without it and then it will re-appear ... comes and goes. I called David Belles and he told me the issue was likely a quality of electricity problem which was exciting the torroid transformer. (I live in a large apartment building in Manhattan.) He recommends a RF filter. Can anyone recommend a RF filter brand? Would something like a Blue Circle Noise Hound or PS audio ultimate outlet/power conditioner serve this function? If it is a electrical problem I don't think it's coming from within my apartment. I've unplugged everything that I can and the hum persists. Help it's driving me crazy. I may be imagining this but when it does hum the system doesn't sound as good. High frequencies are really grating. Thanks in advance for any suggestions.
tooter
bigtee
803 posts
 
If anyone in your vicinity has a light dimmer or similiar device around(off of the same feed in your building) or in your apartment, this could be the culprit.
I looked for a week trying to find why my Belles amp had a humming transformer. Part of the time it was dead silent, then it would hum. I finally traced it to a Leviton dimmer in one room of the house. I replaced that switch and it hasn't hummed since.
The switch does not need to be on the same feed from your breaker. My amp was upstairs on a dedicated 30 amp service. The switch was downstairs on a 15 amp line.
mattybumpkin
590 posts
 
I second Bigtee. I had same problem with a halogen light. On the light's low setting, my amp hummed like crazy. Switch it to the high setting, it basically went away. Toroidal's are very sensitive to this type of stuff.

Regards,
tooter OP
85 posts
 
Thanks for the responses guys. Actually I have 3 lights in my apartment that have dimmers but I always make a point of turning them off when I am listening to my system. Is it possible they are putting garbage into the line even when they're off? I think I will try replacing the dimmers with regular on/off switches.

If it turns out not to be something in my apartment causing the problem but say my neighbor. Would something like a power regenerator fix this? I've always been told not to use any sort of conditioning on my amp but I don't think I can live with this hum. If it's quiet, I can hear the hum across the room, 20 feet or so.
tooter OP
85 posts
 
One more question ... Are all torroid transformers equally susceptible to this electrical hum? Does it have to do with the size of the torroid or is it more related to how the amp is built/designed? I guess what I'm trying to get at is, in the future if I decide to change amps am I going to have the same problem? Thanks.
rhyno's avatar
rhyno
649 posts
 
just b/c the mounting of the transformer to the chassis is tight doesn't mean that its not the cause.

leave the lid off, next time it hums, go put your fingertips only (carefully! do not touch another thing!) on top the transformer and feel if its a mechanical hum or an electrical one. fingertips are sensitive enough to tell...if the transformer is moving, raise it off the chassis & put some rubber gromules inbetween the mounting plate of the transformer and the chassis.
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