Re: [AH] MIDI wiring mess

From Michael E Caloroso
Sent Thu, Dec 27th 2018, 02:02

While we're discussing studio MIDI wiring...

...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.

I was gigging my road system and was experiencing intermittent MIDI
errors.  After finally being able to reproduce it at home, I figured
out that the metal shell of the MIDI plug shorted to earth ground via
the metal DIN jacks I was using on my DIY I/O panels.  Stray shield
wires from the cable had contacted the cable clamp of the plug
(despite my best attempts at trimming the stray wires), completing the
short circuit of MIDI ground to earth ground.  MIDI gets very upset
under this condition.

I use an EBTech cable tested after I build all my DIY cables, and it
does not have the capacity to detect a short from the shell to any of
the pins - it's not supposed to.  Even with my diligent testing after
completing a cable, this bug had eluded me for YEARS in my studio
system.  Yes I was well aware that the MIDI specification grounding
system is designed that way FOR A REASON.

The only way to guarantee complete isolation of MIDI ground from earth
on the metal shell of the plug was to disassemble the plug and add
shrink tubing over the trimmed end of the cable.  This separates any
stray shield wires from the metal clamp of the plug.  Once I fixed my
cabling for the stage rig, it behaved MUCH better.

Nasty bug, this.

For years I had wondered why my SYSEX dumps were never 100% reliable,
now I know why.

That's just the STAGE rig.  Now I have to make the cable corrections
to my STUDIO system, which has easily over 30 DIY cables that I built.
Guess how I am spending my holiday break...

Sent from my iGroundingCanBiteYou,
MC