I haven't been playing with retro computers or games/software recently, basically soon after I posted this it became a worm in my brain. A few months' worth of limited spare time, and some futzing around with FreeCAD and KiCad, and I have my first self-designed PCBs on the way from China for this: I call it the "MiniSynth 32" so as not to annoy any trademark holders, but it's 50% scale of the MT-32. I can't release the 3D models or PCB designs yet because I need to run it past my employer (even if it's released as open-source they have the option of retaining copyright), so it's at least a few weeks out for that, plus it needs some more fine-tuning, possibly another revision of PCBs, hours of swearing at 3D printers etc... The piece of paper over the GPIO pins is a printout of the rear PCB, it will sit at the level of the top of the case with the power/switch/DAC hanging upside down from it. The other PCB is to mount the buttons and OLED to the face plate, I've currently got a handmade one there made of protoboard. The rotary encoder for the volume dial is a tight fit so it's held in with a printed backplate, and the wires are soldered directly to its legs. The mt32-pi project says they plan a full 10-button control system, but it would be a fair bit trickier to get the buttons down to 50% scale.