
I needed a utility box for my band. The goal was to have essentially and A/B/C switch so 1) no cord switching is needed for the Aux Guitar and Aux Keyboard (they are not used at the same time), but also 2) be able to use the Supro as a "country stack" (2nd amp for the main guitar) when the Aux is not in use. Here is the design I came up with:

The 3PDT are being used as 2PDT, I built this in a pinch with parts on hand
It doesn't look as crappy IRL, I swear...
All the sound goes where it needs to be, but this @#$%ing thing hums like crazy!!! Only the keyboard input is quiet, I've tried multiple guitars and all the jacks and they are really hum-infused. This box is a paper weight currently.
I'm sure it is ground noise, but I wired the ground scheme to the best of my meager knowledge. Help, please!
Can someone please tell me how/why I am stupid? Also, any advice on fixing the hum problem would be clutch