[sdiy] Odd ground loop?

[David Ingebretsen]

Hi all,

First, I solved this problem, but don't understand why what I did fixed it.

Simply, I have a midi interface (MOTU Midi Timepiece, (MTP)), a firewire
mixer (MOTU 828 MKIII), a Moog Voyager Rack mount, an old Kawai K1, a midi
controller keyboard, and various modules (still in process of building).

Assume all are connected to the same power conditioner (yes I tried this).

When I connect the audio out of the K1 to the 828, and the Midi out of the
K1 to the Midi channel 1 in of the MTP, I get a bizarre clicking and low
frequency noise (not a hum, weird noise) in the audio. Disconnecting either
the Midi or the audio from the K1 fixes it. Connecting the Midi out of the
K1 to channel 2 on the MTP fixes it. 

The same thing happens for the Moog so I don't think it's the K1. For the
Moog, it happens if I use the balanced or unbalanced audio outputs, too.

Now, if the midi out from the midi controller goes into the MTP on channel
1, no problem and I can connect the K1 and Moog to any other input on the
MTP. No noise.

Like I said, I fixed it simply by hooking the controller to channel 1 and
the K1 and Moog to other channels and that works fine. I would just like to
understand it better.

Any thoughts? Is it a bad ground connection on channel 1 inside the MTP? Or
is it actually the way the grounds are connected internally on the MTP? Or
something completely different?

Thanks,

David


David M. Ingebretsen M.S., M.E.
Collision Forensics & Engineering, Inc.
2469 East Fort Union Blvd. STE 114
Salt Lake City, UT 84121

801 733-5458 Office
801 842-5451 Cell

dingebre at CFandE.com
dingebre at 3dphysics.net