The MIDI Association has released Recommended Practice #54 covering the use of TRS connectors for standard current loop MIDI. If you’re not a member of the MIDI Association, I strongly recommend becoming a member. Among other benefits, members have access to the Association’s on-line specifications and recommended practices.
Without putting too fine a point on it, the diagram from RP#54 says nearly all. [Click image to enlarge.]
MIDI device designers are facing the same sort of space issues as phone developers. The physical form factors are getting too darned small! In many cases — no pun intended — connector size is a limiting factor. Old school 5-pin DIN connectors are enormous relative to slender product envelopes. The MIDI Association recommends 2.5mm TRS connectors and a maximum adapter cable length of 2 meters.
So, of course, you’re wondering about the MIDI controllers, etc. that you already own. A quick check with a digital meter or continuity checker will determine if your current device is consistent with the recommended practice or not. I checked the adapters with my Akai MPX8 and, yep, the adapters are consistent.
The Korg HNS-4331 MIDI conversion cable is also consistent with the RP #54 convention. Albeit, both the Akai and Korg adapters have 3.5mm TRS plug, not 2.5mm. 2.5mm is a good idea since it would be all too easy to plug 3.5mm headphones or a live LINE output into a MIDI port. Yikes!
The IK Multimedia cable that came with my iRig MIDI is a bit of an oddball. First, the 5-pin DIN connector is male, not female as shown in the diagram above. Further, the pin 4 and 5 connections are swapped relative to the pin wiring shown above. So, if you’re wiring for IK Multimedia, please take care and check things out for yourself using a continuity checker.
Sure wish this recommended practice was available a few years ago…
In case you missed it, here’s the MIDI reference circuit.
Please join and be sure to read the 2014 update to the MIDI electrical specification.
Copyright © 2018 Paul J. Drongowski