I have a project coming up where I’m going to want to combine several audio outputs together. This would typically require the use of a mixer and a number of circuits are available to perform a nice mixing function. But I’ve gone for the cheapest, dirtiest solution possible that fits my requirements. It is just one step up from just combining all the outputs together (which you really should not do!). It is a simple passive mixer circuit.
Warning! This is really one of those projects you don’t want to plug into anything expensive or important. This is as crude as it gets in terms of features and could damage an expensive amplifier or speaker setup if used as described in this tutorial!
If you google for “simple passive mixer circuit” you’ll find a number of tutorials and circuits that explain the concepts and provide more robust solutions to this one! Here are some better places to go to, to read up on the theory and decide for yourself.
- Audio Signal Mixing (Elliot Sound Products)
- Simple Mixer Schematics (All Electric Kitchen)
- Simple Audio Mixer (CircuitLib)
Any one of these will give you a much better result, but this one does the job for me.
If you are new to Arduino, see the Getting Started pages.
Parts list
- 6x 10kΩ resistors
- 3.5mm stereo jack socket (PCB mounted)
- Stripboard, male and female headers
The Circuit
The circuit is quite simple. It takes all inputs and passes each through a resistor and then combines the output. The way I’ve wired mine up allows it to be either a three channel stereo mixer or a six channel mono mixer. There is a jumper in the middle of the board that will link the left and right channels together to create the mono mixer.
I built mine on a piece of 6×12 protoboard as you can see in the photos and used the legs of the resistors for linking up the pads.
Closing Thoughts
There are many issues with a passive mixer like this – the output is heavily dependent on the number of inputs, the levels of one input affect the others, there is no means to change the levels of the mix, and so on, but as I am anticipating combing several very similar signals, this should do the trick for me.
As I say, don’t expect significant audio quality and don’t use it to feed a signal into or take a signal from anything expensive!
Kevin
Simple DIY Electronic Music Projects 
what would changing the wattage of the resistors do?
LikeLike
I don’t think the wattage would be significant for an application like this. I can’t imagine there being significant current involved, so I expect any type of resistor would be fine, but as I say, I’m not really an electronics person 🙂
LikeLike