[sdiy] MIDI cable impedance and MIDI In ESD protection?

Mattias Rickardsson mr at analogue.org
Wed Jun 26 15:14:53 CEST 2024


Roman Sowa <modular at go2.pl> wrote:

> 200pF/m will give you good insight of what might happen in the most
> random and unsuitable cables people might try to use.


Thanks!

Ben Stuyts <ben at stuyts.nl> wrote:

> A 6N138 only provides 2500 V insulation between input and output. ESD can
> easily go higher (>= 15 kV can happen), so it might be a good idea to also
> put ESD protection to ground. Be sure to use low-capacitance ESD protection
> or you wil get nicely rounded midi data. No highs. :-)


This was one of my main concerns: Is it "allowed" to have the optocoupler
LED pins connected via capacitors to the ground of the MIDI receiver, from
which it is supposed to be galvanically isolated?

(The MIDI standard mentions allowing two small caps to receiver ground from
MIDI In pin 2 (transmitter ground) for RF shielding and from MIDI In shield
for EMI/EMC performance, but nothing about the two MIDI In signal pins 4 &
5.)

/mr
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