Seventh Circle Audio

I have had a J99 for a year (John Hardy 990C's) with no problem. After moving, I have some serious hum. It varies with distance from the power supply, gets louder when I turn up the preamp (very loud at position 7 and up), and does not change pitch when I move the power cable or the mic cable. The sound occurs regardless of whether a mic is plugged in. My A12 does not hum. Ground lug is secure, thumbscrews are tight, and switching to power ground adds a lot of ground loop noise.

The only way I could appreciably reduce the hum was by moving the module further from the power supply or by covering the PSU with tinfoil. All solders and caps are in good shape. Anything else I should try, or should I send this one in?

Thanks all,
Albert

So it worked fine for a year, but now it doesn't?

Yes. It started after I moved across the state. Maybe the vibration of driving might have jostled something? All my ground lugs are secure, though.

Is what you're hearing a low frequency hum or wide band hiss?
Have you changed the cables connected to the output?
Does the output run through a patch bay?

No low-frequency hum... it's more of a buzz. I've tried changing cables, and there is no patch bay.

Problem fixed--I put the pres in a rack and grounded everything to a copper pipe, noise is gone. Thanks for the help though

Glad you found the problem.