The passive mixer is housed in a 3D printed case. The case consists of two parts: a lid and main body. Both parts print with no supports.
The STL files can be downloaded directly here or from Thingiverse.
The lid has cut outs for the potentiometers and audio jacks to mount to.
The lid also has indented text on the front to label the potentiometer and audio jacks. You can program in a filament swap to your slicer so that the text stands out.
The lid and main body are designed to snap fit together, making it possible to open and close as needed without any additional hardware.