[sdiy] M-Audio Midisport Uno Wire to pin ?

Pete Hartman pete.hartman at gmail.com
Wed Jan 18 18:44:46 CET 2023

On Wed, Jan 18, 2023 at 11:29 AM ShedSynth via Synth-diy <
synth-diy at synth-diy.org> wrote:

> An update: I have just bought a M-Audio Midisport UNO.
> And I’ve got myself a hum-loop:
> The shell of the UNO’s USB-A plug has a connection to the shell of the
> MIDI OUT plug (but not to the shell of the MIDI IN plug).
> And my home-built MIDI module (https://shedsynth.wordpress.com/midi/) has
> a metal DIN socket on the front panel which is grounded through the rack.

MIDI IN isn't supposed to be grounded, and I believe this is the reason.
But you're saying it's not deliberately grounded, but going through the
panel & the rack?

My quick/dirty idea is wrap a piece of electrical tape around the outside
of that DIN socket so it doesn't make contact :-D

> And it doesn’t seem to work with my MIDI module:
> I measure the UNO’s MIDI OUT signal level at 3.3V, which doesn’t seem
> enough to light up my 6N138 with recommended 220R series resistor.
> The UNO variously does or doesn’t play through my other MIDI devices.

What's the voltage drop across the 220R?  This is supposed to be a 5mA
current loop, so you should see about 1.1V.  If you don't see that, I would
suspect the UNO itself.

The "classic" driver circuit uses 5V to drive the loop, if you think that
the lower voltage you're seeing on the UNO output is part of the problem,
you may want to try dropping the 220R to 150R?

Do you have the connections to the DIN socket correct?  I have always had
to read the spec 3 times before I'm sure that I have them going the right
way.  A lot of the pictures of DIY circuits online either 1) don't label
pins 4 & 5 and 2) don't make it clear whether it's showing a front view or
rear view with respect to the DIN.

Like this one for example: https://i.stack.imgur.com/VmuRr.png

Hope this helps....

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