[sdiy] Caution with DIY MIDI cabling

[ASSI]

Am 27.12.2018 um 03:14 schrieb Michael E Caloroso:
> I build my own I/O panels for my racks, and my own MIDI cables.  I
> recently uncovered a nasty bug that has perplexed me for years:
> 
> If you use metal shell MIDI plugs on your DIY MIDI cables, DO NOT
> ALLOW MIDI GROUND TO COME IN CONTACT WITH THE SHELL.

Well, that is actually explicitly specified in the MIDI electrical spec. 
  MIDI is a 5mA current loop optically isolated at the MIDI input 
(receiver end), and the cable shield must not be part of it.  There is 
no "MIDI ground", as the loop is isolated and actually referenced to +V 
for the current source.  The reference voltage used to be 5V in MIDI1.0, 
but there probably is equipment by now that provides 5mA through pin4, 
but not necessarily 5V, so you'd best not rely on any specific voltage.

MIDI cables: Pin 2 (cable shield) and pins 4 & 5 (current loop) are 
wired straight through, pins 3 & 4 are left unconnected.

-- 
Achim.

(on the road :-)