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

ShedSynth shedsynth at gmail.com
Wed Jan 18 19:21:17 CET 2023

Thanks Pete.

On a lucky guess, I swapped the 6N138 chip (no other component changes) and now working OK.


I’ve been testing with two other MIDI sources:

M-Audio FastTrack Ultra, 5V signal, no problems.

M-Audio MidiSport 2x4, 3.3V signal, no problems.


And now M-Audio UNO, 3.3V signal, no problems

…apart from that pesky ground issue

…and it doesn’t work with another sound module, but not investigated that very far yet


And thanks Harry for the adapter suggestion.





From: Pete Hartman <pete.hartman at gmail.com> 
Sent: 18 January 2023 17:45
To: ShedSynth <shedsynth at gmail.com>
Cc: synth-diy at synth-diy.org
Subject: Re: [sdiy] M-Audio Midisport Uno Wire to pin ?




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