It could also be caused by power cables crossing over patch cables or even
be caused by something sitting to close to a power supply or amp in a rack.


Jon Myatt wrote in message
.. .
I have what appears to be a ground loop, and it's driving me *mad*.

My S90 keyboard is plugged into my ST Audio DSP24 C-Port sound card (well,
rack).

The balanced outputs of the DSP24 then go to the power amp.

When the S90 is connected I hear a constant whirring in the background,
which gets worse if I move the mouse. Disconnecting the S90 makes it go
away.

I've tried about five different pairs of jack-jack leads - all the same.
Other devices plugged into the DSP24 are fine. The S90 plugged into the
power amp directly is fine.

Any suggestions? I'm tempted to ditch the DSP24 and buy a Motu or
M-Audio...

Thanks,

Jon.


Remove the obvious from my address to mail me. Thanks.