what does it do?
A lot of fun

the main PCB contains 10 relay, all switched at the same time.
the first eight have two 26 pin IDC connectors, relays no 9 & 10 molex, for inputs A & B (I use them for switching MIDI, and mute MIDI thru to prevent MIDI loops if switched to B)
outputs are again one 26 pin IDC and molex.
the 26 pin IDCs have Tascam layout, if you prefer SubD connectors.
the other PCBs are passive, 8 x Neutrik NC3FBV to IDC 26,
and IDC 26 via 8 x Neutrik NTL1 transformers to 8 x Neutrik NC3MBV for outputs.
just a simple A/B switch

didn't want to wire it by hand, so I designed the PCBs with options for SubD25.
the older version just needed too much time doing the wiring:

All the other parts are just PSU(s), and an optical Click system.