2. amps-preamps
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Strange Hum from Right Pre Channel Only

My tube preamp has developed a peculiar hum problem only in the right channel, and it began only after I switched to XLR cables running from the preamp to the XLR inputs on my Krell FPB 300cx amp. I never had this problem when I used RCA’s from the pre into a RCA/XLR adaptor attached to the amp inputs.

Strangely, when I switch L/R channels for the XLR cables attached to the pre, the problem goes away, but now I have Left pre out to Right amp in, and Right pre out to Left amp in, not an optimal arrangement.

Please advise what could be causing this right channel hum and how I can remedy it, other than by reversing the channels on the pre end.

Thank you.

Neal
nglazer
steuspeed's avatar
steuspeed
501 posts
 
Ground loop. Try using a two prong adapter on your power cables until you find it.
xti16
1,525 posts
 
Strangely, when I switch L/R channels for the XLR cables attached to the pre, the problem goes away, but now I have Left pre out to Right amp in, and Right pre out to Left amp in, not an optimal arrangement.
Doesn't sound like a ground loop. I would expect a ground loop hum to be in both channels. Almost sounds like a bad connection somewhere and by reversing the cables you got lucky. I would first try wiggling the connectors to see if the hum comes back. If nothing try putting tension on the cable close to the connector. I would do this to both cables at both the pre and the amp side. I'm guessing since this happened with the new cables it's a cable problem. But it could also be a connector on the device that had the rca/xlr adapter.

Just saw the duplicate post.
czarivey
5,680 posts
 
if your preamp is old, than it may need service.
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