Ground Loops via USB

[HCMarkus]

Had a nasty buzz. No drugs involved. Dim the lights, set the mood, there's that buzz again. What's up?

I've always noticed my Motif ES is sensitive to grounding. Tried all the usual things: Plugging all devices from one outlet, cutting ground wires on audio connections, even lifting the ground on the Motif and other devices' AC. But still, a subtle ungood buzz remained, robbing delicate mix moments of transparency.

Turns out that a potential exsts between my MOTU 828mkII Firewire ground and the Motif ES USB ground. Fixing it was simple: cut and pull back the plastic sheath on the Motif USB cable, remove a short section of shield and cut the black (USB gound) wire, one of four within the USB cable. Viola! Dead Quiet.

I mention this as an FYI, something to file in the back of the mind. The black wire in a properly-wired USB cable carries the ground, and can be removed as long as there is an alternate path to ground, like through an audio cable or AC grounding. Now, I am going to re-mix the tune I am working on, free from inharmonious grunge. I'm feeling good, riding a no-buzz high!