Passive Stereo 2-channel Audio Volume Mixer

Required tools & materials

~60g PLA or PETG or ABS
- circuit board 30x70 mm
- 2x stereo 75 mm B103 10K sliding potentiometer. Do not use the red one in the picture. https://www.amazon.pl/dp/B081JNQ7MM

- 2x tactile latching 6 pin push buttons (for muting) 8.5 x 8.5 mm https://pl.aliexpress.com/item/1005003333312190.html

- 4x M3 bolts (sizes from 5mm to 12mm will work)
- 3x 3.5mm Female Audio Connector PJ-320A (TRRS or TRS, in this project I'm using TRRS)

- pliers, wire cutters
- soldering iron, solder, colophony, brass sponge, 3d printed vise
- wires (flexible silicon insulated are recommended)

- multimeter (highly recommended for checking wiring)
- 2x silder knob, ex https://www.printables.com/model/1219170-knobs-for-passive-stereo-2-channel-audio-volume-mi or https://www.printables.com/model/106132-fader-slide-potentiometer-knob

Note! This mixer handles TRS plugs only, but the female connector can be TRRS or TRS.

Case printing tips

Use support for holes (bottom part) and slider cutout (top part).
Use support blocker for the potentiometer “beds”

Assembly

Solder the components according to the schematics (wires of different colors do not intersect). Black wire is ground (common).

Test your mixer before putting it into the case. Use multimeter for debugging.

Make sure to leave some slack for the wires, so they don't break when put inside case.

Place push potentiometers into bed. They should fit tightly without glue. 

Use pliers to clip-in female sockets into place.

Place buttons on the bottom part, so they match the cutouts on the top. Screw top and bottom parts together. Watch out, so you don't pinch any wires.

Hint #1

You can use the volume mixer instead of the y-splitter to control output independently if you modify the internal wiring. 

Hint #2

You can use this device to control headphone volume of headphone which don't have a physical volume control, ex Sony WH-1000XM series headphones etc.

Note: The picture of the internals of my audio mixer show additional 2k (blue and round) potentiometers. These are optional (for fine tuning). I have left them pass trough, no resistance.