[sdiy] Odd ground loop?

[harrybissell at wowway.com]

I had a MIDI box that had the 5V regulator tab tied to the chassis...
that made for a unique ground loop as well. A mica washer fixed the problem
neatly.

H^) harry




On Sun, 21 Dec 2008 13:45:32 +0000, Seb Francis wrote
> Make sure also there is no connection in the cable to the metal DIN 
> plug shell (you are using a proper MIDI cable, right?).  The cable 
> shield should only connect to pin 2 (the middle pin), not to the 
> plug shell.  See here: http://www.philrees.co.uk/midiplug.htm
> 
> If this is ok then maybe your MTP breaks MIDI spec by connecting the 
> ground at the MIDI input.  Try making/modifying a MIDI cable with 
> ground pin 2 disconnected at the input end.
> 
> Seb
> 
> David Ingebretsen wrote:
> > 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
> >
> >
> >
> > _______________________________________________
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> > Synth-diy at dropmix.xs4all.nl
> > http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> >
> >
> >
> 
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Harry Bissell & Nora Abdullah 4eva