Simple 3-Channel Stereo Mixer with VU Meter

Dear Readers, please welcome a new contributor Colin Merkel. His projects include an impressive built from scratch micro controller based looper and now a simple Stereo Mixer.  I’m sure this will be useful in circuit bending applications. It is worth noting that the project below was built from spare parts and could be done much smaller if needed. – CM

My name is Colin Merkel, and recently I have been annoyed by the audio setup in my room. I have some really awesome speakers, but they are usually attached to my computer-when I want to plug my iPod in, or anything else for that matter, I have to fiddle around with 3 different cables – very frustrating!

So, to fix my problem, I put together a simple 3 channel stereo mixer.

Mixer

As you can see from the photograph, there is an analog VU meter, one volume knob and mute switch per channel, and a master volume control in the form of left/right level sliders.

The electronics behind the system are extremely simple- in fact, I used only a single LM324 quad op-amp, some resistors, and some diodes. The entire circuit runs off of a 12V DC wall wart power supply. Shown below are poorly-drawn schematics for the left and right channels.

As a possible improvement, I may add a headphone jack on the front so that you it would be easy to put all the mixer output through headphones. Here are some photos from the build:

Breadboard layout
Testing on the breadboard!
Soldering the circuit...
Completed circuit
Completed circuit
Have to keep good notes...

Anyway, the mixer was an easy build that managed to make my audio system a little bit more awesome. Thanks for reading! If you have any comments or questions, feel free to ask.