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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
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.
tooter OP
85 posts
 
Thanks for the tip Rhyno. I definitely would not have thought to try that. Hopefully I can get this figured out quickly!

Tooter
bigtee
803 posts
 
Belles mounts his transformers very well and they are isolated. Unless the transformer is physically defective, I doubt that is where the problem is. It's something coming in on the line. Otherwise, it would hum all the time.
Good question about whether they all would do this. Most amps I've used in the past had an E-core.
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