DIY MIDI Thru Box, Version 2

IMG_7166I’m very pleased to announce that a PCB, panel or complete DIY kit of this project is available to purchase fromĀ


I needed an extra MIDI Thru box so I dusted off the project that I’d previously done. However, I decided I wanted to re-box it, so that it would be more in keeping with the gear I’m making now. I also removed a few frills along the way (bye, LEDs and power switch!), rationalised the board design and made the whole thing about 40% smaller as a result. Essentially, though, this is a cosmetic facelift – it’s still the same circuit design inside.



Build Documents

Schematic (Board)

MIDI THRU v2 Schematic Board

Schematic (Panel)

MIDI THRU v2 Schematic Panel

Stripboard layout

MIDI THRU v2 Board

Stripboard layout (flipped)

MIDI THRU v2 Board Flipped


My panel design and cutting guide are available below as 600dpi PDF files.

MIDI THRU v2 Panel

MIDI THRU v2 Cutting Guide





9 Comments Add yours

  1. Kripies says:

    hi! first of all, thanks for sharing your projects!
    I want to make a midi thru box, but I’m a bit confused as to the optocoupler used. in the “good” appears the 6n137, but in the schematic appears 6n136. I realized that in other projects you used both.
    Which do you recommend to use for this project ?? 6n136 or 6n137 ??


    1. Morocco Dave says:

      I started off using 6N136 but I find 6N137 easier to source locally. For the purposes of this project they’re interchangeable – you can use whichever you find easier or cheaper to get hold of. Good luck with your build!


      1. Kripies says:

        ok. Finally I will try 6N138


  2. Lukas Jurk says:

    Hey, big thanks for your great tutorial. I have successfully build it. But how can i extend the number of midi-out ports. My Idea is to take another 74hc14n. pin 7 to ground, 14 to 5 v and connect pin 1 with pin 2 from the first hex-inverter and then do the same like with the first. Would it work?


    1. Morocco Dave says:

      Hi Lukas,
      Yes, that should certainly work. The other alternative would be to just build a second thru box and just daisy-chain them. Good luck!


  3. Aaron Andrews says:

    Hi! Like others have said thank you for sharing this project, unbelievably helpful! I’m less experienced with electronics and just wanted some clarification to what the J1, J2 and J3 headers connect to? I’m assuming J1 is power in, J2 is 5x MIDI out (pins 2 & 4) and J3 is MIDI in (pins 2, 3 & 4)? this may be totally wrong but if not, I’m still unsure on the polarity of the power and arrangement of MIDI pins for the in and outs, any help on this would be really appreciated!
    Thanks again!


  4. Morocco Dave says:


    J1 is MIDI in, J2 is MIDI out, J3 is power in. If you take a look at the schematic above, you’ll find that each individual pin is labelled with its purpose.

    Hope this helps, and good luck!

    Liked by 1 person

    1. I’ll see If I can order a new set of eyes with my components haha! Don’t know how I missed that, thank you for your help!


  5. Dave thanks a trillion man. Thanks for sharing.
    Awesome build and fun too. I finished it and works like a charm…


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