[sdiy] Odd ground loop?

[Seb Francis]

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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