PCB for a 4x4 active matrix mixer
This is a companion module to the passive matrix mixer but is rather more versatile on account of it being active and having a gain control on each of the four channels. If you're a full-on noisemonger then this gives you the chance to get some juicy feedback going if that's your idea of a good time.
If you're not clear on how a matrix mixer works then Wikipedia actually has a decent article on the subject - basically you can route multiple sources to multiple destinations and each can have it's own mix, hence all the pots. Signal routing can be immensely confusing to begin with, and the best way to understand it is to refer to the schematic.
100% through-hole components and an ideal beginners project - the BOM and schematic can be found here: https://bitbucket.org/yorkmodular/matrix-mixers/src/master/ - I recommend the use of Alpha 9mm pots with Befaco micro-knobs, since these will afford a greater degree of support to the panel.