Here are some 3d printed patchbays I made for my modded CASIO SK1 synths. Each plug is a banana jack (you can get 100 of these on ebay for like 12 bucks) and is connected to a pin on the memory chip bus of the main PCB. To understand how to wire one of these up look at the page at CasperElectronics. The point of the patch bay is to connect these together in a myriad of different ways to create unexpected sounds. Basically I think it makes interruptions in how the encoded instrument sample data is sent from rom chip to processor. Skip to the end of this post to hear a sample.
I made lots of design changes to this simple board and printed it out multiple times to get things nice. I still think the font I chose for the letters is a little unsuitable for this resolution of printer.
To hear what it sounds like, listen to some noisy experiments… this is done with a Korg monotribe with the CASIO Sk1 plugged into the audio input.