[sdiy] Caution with DIY MIDI cabling

[rsdio at audiobanshee.com]

Hmm, I think the reason that this is happening is that MIDI In and MIDI Out jacks should be wired differently. MIDI Out should connect the shield ground, while MIDI In should not. It’s easy to manage in a synth, where there is only one of each (well, two MIDI “out” if you count MIDI Thru).

I assume that your DIY MIDI I/O panel was perhaps generic? … so that the panel does not distinguish between In and Out, but depends upon which port you connect internally to the rack gear?

It might work if you had one row dedicated to MIDI In, with isolated ground, and another row dedicated to MIDI Out, where you wouldn’t need to worry about grounding issues. Seems like that would be the only way for a generic panel to work, although you would be limited by the dedicate Input versus Output/Thru designations.

Brian


On Dec 26, 2018, at 6:14 PM, Michael E Caloroso <mec.forumreader at gmail.com> wrote:
> 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 tester 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