Yet Another Analogue Line Mixer

[cgraf]

Gentlemen

since a long time I am looking for a small mixer suiting my needs: 2 Stereo Channel input, 2 Stereo channel output which are easily switchable. The requirement came from the fact that I often do A-B tests, either comparing 2 sources to one amp, or one source to two amps to compare amps. It is not for DJ use.
As I did not find something which totally suits, I tried to come up with my own design.

• Sliders pots for the input and the output
• good sound performance
• small form factor
• Analogue-like VU meters using an Arduino and two small OLED
• Possibility to have a Bluetooth receiver connected, having a rotary volume and which can be switched off using a switch
• two clip leds, also powered by the arduino nano.
• All parts on the PCB

The "software side" is under control, but I am not really an expert in hardware design. Is there an expert who could take a look on the schematics ? Are there any major bugs ?
As a small thanks I would offer two PCB's to the one who could help.

I designed the schematics in EASYEDA Pro, the PCB is not routed yet but the places of the potentiometers, input rca jacks, vu meter is kind of "given".

Inputs will be highly appreciated.
All the best,
Christoph

 

[PRR]

The output not being fed should be shorted to ground or it will pick up hum and stray crap.

Level controls are dubious in A/B testing because if one side is the least bit louder it will be "better". Your box may reduce to switches or relays.