Hum in speakers when connecting RCA cables into BHK PRE

Hey all,
Recently got a used BHK PRE. Everything works great but whenever I plug in RCA cables into one of the inputs I hear a SLIGHT HUM from my speakers… I then replace that input and output with one of my XLR cables and it is GONE. Whats going on here?

The whole point to XLR cables, into a true balanced circuit like the BHK is noise rejection (CMR–common mode rejection).
You can find complete explanations on this forum or most anywhere.


This popped up on my radar and you answered better than I. This is the answer! ^^^

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You probably have a ground loop somewhere in your system. The BHK pre works fine with RCA/unbalanced cables unless you have some gear plugged in (and grounded) in one location and other gear plugged in (and grounded) at another receptacle/branch circuit. You also didn’t mention if the RCA input is from a phono pre which can be very sensitive to grounding from your TT, etc.

You could try to unplug all but the essential gear and see when the hum stops. Then try to plug all necessary components into the same receptacle at least as a temporary test to see if that’s the issue.

Good luck. Can be a bit patience testing these grounding/hum issues. Also, I noticed a couple of my previous phono preamps could pick up hum from light dimmers at a particular setting.

ah yes… the rca from my phono pre DID NOT have hum! what had the hum was when I’d connect my OPPO UDP 205 RCA OUTS into RCA IN on one of the BHK INPUTS AND when I’d connect RCA out from my MARANTZ PRE AMP into one of the BHK INPUTS for HT BYPASS. So once I changed these out for one of my Audioquest Red River XLR’s… hum gone!