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

[Sean Ellis]

It boggles the mind companies would rather have converter plugs (for their inputs only) instead of adding 2 or 3 diodes.

________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Andrei Kudryavtsev via Synth-diy <synth-diy at synth-diy.org>
Sent: Thursday, 27 June 2024 8:55 PM
To: Martin Klang <mars at pingdynasty.com>
Cc: Synth-diy <synth-diy-bounces at synth-diy.org>; Mattias Rickardsson <mr at analogue.org>; synth-diy at synth-diy.org <synth-diy at synth-diy.org>
Subject: Re: [sdiy] MIDI cable impedance and MIDI In ESD protection?

Speaking of TRS mess, found this one in the recent application list for MIDI innovations:
https://midi.org/innovation-award/psimidi

On Thu, Jun 27, 2024 at 7:54 AM Martin Klang via Synth-diy <synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org>> wrote:

Well the input, if MIDI compliant, is protected by an optocoupler. Shouldn't that be enough?

I've seen plenty of DIY and not-so DIY circuits where the output comes straight off an MCU pin, which makes it susceptible to over-voltage and current. I'd put a transistor in line at least.



Martin



-----Original message-----
From: Mattias Rickardsson <mr at analogue.org<mailto:mr at analogue.org>>
Sent: Thursday, June 27 2024, 4:29 pm
To: grant musictechnologiesgroup.com<http://musictechnologiesgroup.com/> <grant at musictechnologiesgroup.com<mailto:grant at musictechnologiesgroup.com>>
Cc: synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org> <synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org>>
Subject: Re: [sdiy] MIDI cable impedance and MIDI In ESD protection?

<grant at musictechnologiesgroup.com<mailto:grant at musictechnologiesgroup.com>> wrote:
The latest MIDI electrical spec CA33 shows "optional ferrite beads to  improve EMI/EMC performance (FBx 1K @100MHz)"as well as "optional small  capacitor (0.1 μF typical) to improve RF grounding", along with diagrams.

And I realize that the TRS MIDI spec (RP-054 from 2017-18) writes an unspecific answer to my other question:

"Because TRS connectors are often used for other (non-MIDI) purposes, manufacturers are strongly advised to add protection circuitry (e.g. to handle the case when a DC-coupled headphone driver is connected to a MIDI output)."

In the world of massive Eurorack systems and tiny plastic synths I expect that pretty loud signals are sometimes connected to MIDI Ins & Outs when confusing TRS MIDI with audio cables. But I wonder what the MMA would suggest that this protection is made, not only in the output case that they mention as example. :-)

/mr

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