Working on the BulkyMIDI-32 Internal I made the choice of using TRS sockets for the MIDI-signals, thinking that was an easy way to get it connected up to my other equipment - as that would just require buying such a ready-made cable. Unfortunately though, the ones I had ordered up from China were simply wired up wrong - they were intended for audio and did not match any of the known pinouts for MIDI. I did order them up from a music store, but they've been delayed so many times that I just wanted something that I could rely on!
Myself. Meaning that I threw together this adapter, allowing me to use a standard 3.5mm stereo audio cable for MIDI-purposes. Yes I could probably have just ordered one from a really expensive store and have it delivered within a week from international site for professional musicians that know what they are doing, but I didn't like the fact that a short little cable - would somehow end up being the most expensive component when building an MT32-PI.
Helpfully enough, there are two competing standards for how such a thing should be wired - commonly referred to as type A and type B. A simplified guide to MIDI over TRS minijacks goes into all of the detail that you would ever need to understand for the both of them. In practice when it comes to the adapter that I made, there's a set of jumpers that need to be set according to the equipment you're using - either horizontal (type A) or vertical (type B).
Building the device should be a straight forward affair, you just solder the two components into place. Just don't burn yourself while doing so. Some 5-pin TRS socket types may have little plastic "nubs" underneath them that you may need to snip off to make it sit perfectly flush, but most will fit.
The supplied KiCad files should be sufficient as both a schematic and as a starting point for ordering PCBs (basically you could just zip the contents of the export folder and upload that on a fabrication site), the schematic is also available in PDF-format and this is what you'll need to print and work your way through when things fail to work as expected.
Most parts should be easy to get a hold of from your favourite local electronic component shop, but given that I don't have access to such shops where I live so everything was based on whatever I could get cheapest from eBay/AliExpress (free shipping, but plan on waiting 3-4 weeks for delivery).
| Reference | Item | Count | Order |
|---|---|---|---|
| Faceplate PCB | Fabricate using Gerber files | 1 | PCBWay |
| J1 | PJ-307 3.5mm socket (alternatively PJ-317) | 1 | |
| J2 | Female S-terminal 5pin DIN PCB | 1 | |
| J3 | Straight pin headers, with two jumper caps | 1 | |
| 3.5mm TRS cable (M-M), preferably of decent quality | 1 |