I've had the same problem with hum useing xlr's. Try running a ground wire from your preamp to the amps.
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Why in the world would you install a balanced cable if it only causes hum? The only reason to use a balanced cable with XLR's is to eliminate noise. If it makes more noise, why not just use the single-ended? Why attempt exotic, expensive and potentially dangerous (lifting grounds can be deadly) solutions to a problem you can eliminate by simply going back one step? Your amplifier is probably not a balanced design, and no amount of fiddling with balanced cable will get it to run quietly.
You didn't list your components, and I gather they are of diffent mfg. Use a meter/ tester, and check for phase, continuity, etc., of the 3-pins at each end of cable.. If checks out Ok, Take apart the Male XLR and notice how it is wired. If shield is connected to Pin #1, snip it. Same goes for if shield is connected to shell. Also, if a strand from shield is touching shell that may be the problem also. Signal Ground is touching chassis Ground and causes hum from Ground loop. A .10uF ceramic cap from Pin 1 to chassis cures the hum also 9 0f 10 times. If all gear isn't Balanced, its really worthless with most home audio gear. Also mixing different Bal gear causes as many noise problems. Compatability is the answer. If it sounds good with SE cables leave it alone. Good Luck! Charlie CS Audio
Thank-you Brianmgrarcom!! Once I put the plugs on to short the RCA inputs on back of amp, The Hum went away!! If I would have read the manual, I could have saved myself alot of time and hassel. To the above parties, My equipment is totally balanced and of the same manufacturer!! Thanks again to all input. Steve
I just had the same problem, once I installed my first XLR interconnect between my SF Line-3 pre-amp and Plinius power amp. A low frequency buzz came out. I tried cheater plug in all my pre-amp, phono stage and amp plug. It did not work. My amp did not come with RCA plug. I shorted it with ordinary RCA line and did not work either. Might need to change back to RCA line and save the XLR line for the future.