[sdiy] Who apart from me things the whole MIDI board needs replacing ?

Mattias Rickardsson mr at analogue.org
Wed Jan 26 20:38:22 CET 2022


Tom Wiltshire <tom at electricdruid.net> skrev:

> So does the 3.5mm TRS MIDI not-Standard connect the ground of the TRS lead
> at both ends, or only one like DIN MIDI? And does it use opto-isolation in
> the same way?
>
> If so, it's basically just a change of connector for something of a
> smaller size and I don't see any problem with it. If the good features of
> the original standard also got dropped in the change, that seems like a
> somewhat retrogressive step.
>
> While I can see that if everyone was using 3.5mm perhaps it made sense for
> the standard to reflect that, 3.5mm is alos used for audio input/output on
> a gazillion devices and people are absolutely bound to try connecting it,
> just to see if it works. 2.5mm is less common and prevents that to some
> extent.
>

The specified cable for TRS MIDI is shielded twisted pair, why it kind of
makes sense to specify a non-audio-standard connector for it, so that
people don't just take any eurorack cable. (Who would do such a thing?) .-)

https://www.midi.org/midi-articles/trs-specification-adopted-and-released

There are some interesting passages in the standard actually, it can be
downloaded with illustrations on the page above, but some of it in plain
text:


"Details:

(1) Pin-out Correspondence:
The following TRS to DIN drawing illustrates the wiring for a female TRS
connector in comparison to a
female MIDI-DIN connector (it is expected that devices will use female TRS
connectors).

Notes:
The MIDI In/Out circuitry should be implemented in accordance with the MIDI
1.0 Electrical
Specification Update [2014] (MMA/AMEI CA-033).
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).

(2) Connector Size:
2.5mm TRS connectors are recommended.

Note: If any other connector size is used, the remainder of this
specification still applies.

(3) Cables
All cables shall use shielded twisted pairs, as defined for a MIDI cable.
The following drawing shows how to implement a male TRS to female MIDI-DIN
adapter cable:

Notes:
Adapter cables shall have a maximum length of 2 meters.
Direct connection between two TRS-equipped devices using cables designed
for use with audio
equipment is not acceptable because the wires are not twisted pair and are
typically individually
shielded."
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