2. amps-preamps
  3. 1432746902

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
atmasphere's avatar
atmasphere
11,807 posts
 
An intermittent connection in the XLR cables sounds the most plausible from everything presented so far as Xti16 suggested.
nglazer OP
846 posts
 
Thank you. I do not think it is a ground loop. I suspected an issue with the XLR cables. These are HiDiamond top of the line XLR's IC's and I have to see if there is anywhere in the USA I can have them looked at.

Very mysterious. In 40+ years of this mania I have never had this occur.

Neal
atmasphere's avatar
atmasphere
11,807 posts
 
I've had it happen exactly that way a few times. Next time you have a problem, see if moving the cable at the input to the amp can make it come and go.
nglazer OP
846 posts
 
Thanks for suggestions. I will try Atmasphere's suggestion. In the meantime, some other pieces of evidence:

When I use the XLR cables directly from DAC outputs to amp XLR inputs, i.e., using the DAC as a preamp, there is no hum.

When I switch the cables completely from pre to amp, i.e., what was left to left now is right to right, and vice versa, the hum REMAINS ONLY in the right speaker. This leads me to believe the cables are not the problem.

Last, when I reverted to my RCA cables into RCA/XLR adaptors on the amp end, no hum whatsoever.

Does this help at all in solving the mystery?

Thanks again,

Neal
atmasphere's avatar
atmasphere
11,807 posts
 
Were you using the same XLR cables with the DAC as you were with the preamp?
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