DIY Midi A/B box

I recently realized how often I am plugging and unplugging my midi cables. What I needed was a midi A/B box which allowed me to select input A, B or none at all to feed my Korg DSS-1 keyboard. After a quick search online I ran across some solutions, but not anything in my budget ($0).

Enter my box of switches and such. I found a cheap plastic project box from Radio Shack that I had, a DPDT (double pole, double throw) switch, a female 5 pin din (midi plug) and an old midi cable that I could re-purpose. All in all it cost me less than $10 in parts, which I already had.

First I split my midi cable and determined which wires fed the three main pins (pins 2, 4 and 5) of the midi cable. The outermost pins are not used and the center pin is the shield pin (ground). I took the 2 wires which corresponded to the remaining pins (pins 4 & 5) and attached them to the DPDT switch. Then I connected the DPDT switch to the female 5 pin din plug. Pin 2 from both cables attaches to pin 2 of the female midi jack. Drill some holes and whammo! Now I can select A, B or no input. This box will also work in reverse. I chose to use the cable in place of more female midi jacks because otherwise I would have needed to buy more midi cables. You can easily substitute jacks for cables or visa versa.

It is easier to explain with pictures, so excuse my drawing, but if you have questions contact me.




6 thoughts on “DIY Midi A/B box

  1. What do pins 1 and 3 even do then? arent the nececarry for other midi applications? I need a box like this for sending a midi clock, CC messages, and note values to my gear. are your pinouts good enough for my needs?

    • Having only 3 pins active is the norm for standard midi information. The other two pins (pins 1 and 3) are for powering some gear which is somewhat rare. Most gear only requires the 3 standard midi pins, so yes this will work for you as long as you are using standard midi gear.

      You would know if your gear required 5 pin active midi cables since most cables are made now with only 3 pins active and you would have run into problems by now with those cables.

      Good luck,

  2. I followed your lead to solve a ridiculous yet killing problem. What a great fix! Above all, none of the MIDI mergers on the market that I looked into would have helped me much, so it had to be a switch.

    It’s one of these tip that helps you get more focused on the music and less on the equipment so it’s really worth the effort.

    I had to figure it out you cannot mix MIDI cables with various impedance&resistance, but then splitting a cable is perfect. On both cables I butchered (and repaired afterwards), the active wires were the red (signal) and the white, you can try with these first. The switch I obtained from the local guitar shop, a few bucks, you have to ask for an ON-OFF-ON switch if DPDT says nothing to the shop guy. For the box I used a transparent box of cotton ear sticks found in the bathroom… it’s not ugly, you can see the wires inside (don’t forget to tie them inside to stop them so that your box lasts longer), and it was literally a piece of destined junk so it’s perfect now in its new use!

    So have fun, thanks again for the good tip, and a happy new year to you!

  3. Is connecting the grounds every problematic for ground loops? Would you connect the grounds to the enclosure? Thanks!

    • No, I did not attach the ground to the box. As of yet I have had no problems though. With midi, it is pretty low voltage and there is no audio for any ground hum to get introduced to the sound. If you want to, you can probably connect all the ground wires together inside the A/B box to be safe.

  4. I followed your instructions and my midi box works great.I built it to use for my Jupiter 6. When you turn this keyboard on, it defaults to omni mode. But if you turn on the unit with a cable connected from midi out to midi in, it sets it on midi channel one only, then you have to remove that cable and plug in the other cable to use the keyboard via midi. Not wanting to mess with cables each time I powered on my keyboards, I use this box and it worked wonderfully. Thanks!

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