Built this at the request of a client: 4 x 4 passive matrix mixer with added format conversion!
Detail: 4 input, 4 output matrix mixer with kill switches on each node (takes that node out of the output path). As you can see, the input (red) and output (blue) section has 3.5mm mini-jacks AND 4mm banana sockets. The bananas are normalled to the switch on the jacks so you have the option on both input and output of routing from/to a banana-jack or mini-jack source. There's also a single banana socket on the other side for grounding purposes.
So there you have it: a 4 x 4 passive matrix mixer that can work in 3.5mm jack or banana and can act as a conversion box to/from mini-jack to banana! All in a box that measures 145 x 120 x 40mm (footprint about the size of two iPhones side-by-side)
Originally built for a client but he's said he doesn't mind if I make them for other people so if you need a compact, flexible matrix mixer (and who doesn't!) then I'm making them for £100 (for a 4 x 4 one). Other colours and size options very possible.
matrix noise drone mixer banana passive