Looking for a hardware switch to control which of two MIDI boxes is the clock master.

The two MIDI boxes - A and B - can each clock synch the other (as well as MMC commands). Both boxes have MIDI INs and OUTs on 1/8" TRS. The switch would control which is the master.

The switch box would have 4 1/8" TRS connectors: MIDI In A, MIDI In B, MIDI Out A, and MIDI Out B. The switch would have two positions:
1: A is the Master, connecting only MIDI In A to MIDI Out B.
2: B is the Master, connecting only MIDI In B to MIDI Out A.

Does such a box exist? or ... Where might I get one constructed?? or ... How might I construct one???

I've tried a software switch using Cantabile, but it does not work (extensively tested) because of jitter in the MIDI signal (tied to ASIO buffering) which makes the tempo derived from MIDI clock signals unreliable.

Any suggestions appreciated ...

Is this because either device needs to be the one to start a composition so want to give it master clock duties? Trying not to dive into an XY Problem until I understand the underlying problem that brought you to this idea.

I would normally just say use a dedicated clock device like CLOCKstep or CLOCKstepMULTI all the time and make neither of the other 2 devices master clock.

**Thanks** for assisting @ Joe_K !

Yes, I sometimes want Device A to be the master, and sometimes Device B. A is a looper (and I sometimes want to use a live loop to dictate the tempo) and B is a drum machine with adjustable tempo that I sometimes want to dictate tempo, and I don't always know what the numeric value of the tempo is from device B.

I had a horrendous design with multiple Kenton midi splitters and merge boxes and two separate off-the-shelf MIDI kill switches, but that was overkill ... I really think this should be as simple as one box, one switch, four inputs ...

Also seems like this might be a somewhat common issue that could maybe spawn a commercial product??

Yeah, I would think a MIDI Hub (a combo Merge and Splitter box with multiple Ins & Outs) would be a thing you could use, but that would be active and micro-processor based, not passive. And though something like that would work, you're not really trying to merge or split logically, you are trying to reverse direction.

Have you tried just hooking the devices together in a loop and then turning off each device ability to send THRU or receive INPUT as necessary? It sounds like you would already have to go into each device a change settings related to sending or receiving MIDI Clock, right?

If you want to DIY a passive unit like you describe, I think you could probably do it with a 4PDT switch as long as you don't have to switch the ground connections.