this is my first question and I am very much a beginner in electronics so I apologize if this is a too stupid question.
I have Atari punk console and another small homemade audiomaking circuit. These two have mono audio signals as outputs and I would like to combine these as one in the simplest possible way. I know next to nothing about audio processing but I believe that the strength of the two signals is roughly the same.
What would a neat solution be? It would be really nice if I could extend the solution later on to more than just two signals but thats not really important.
Any hints, references, guides, links or ideas would be highly appreciated.
Best Answer
The simplest way to combine two signals is with two resistors as shown in the circuit diagram below.
simulate this circuit – Schematic created using CircuitLab
The ground connecton is shared between both inputs and output. The quality can be improved by adding an output buffer (opamp), but that complicates things in requiring an IC, power supply, (de)coupling caps, ...
simulate this circuit
The advantage of the lower circuit is that the inputs see a constant input impedance, one that doesn't change with the other signal's level. This improves output quality. Practically speaking the inverting output (-) of the amplifier is virtual ground, which means it is set at a static voltage (4.5V in this case). The series capacitors are required to decouple the DC bias of both in- and outputs, they allow the signal to pass, but block the DC voltage.