Hi. I am designing a very basic audio mixer circuit for use in my car before my amplifier. I need to mix one mono signal, and three stereo signals. I think my diagram is basically correct so far: http://img464.imageshack.us/img464/7110/mixer9lb.jpg I plan to measure the average voltage of the signal of each input when playing the same music, to get an idea as to which ones are naturally stronger than others. Then I will use resistors that are proportional to these values to even the volumes out. However, I am unsure of how to mix the mono signal so that it's replicated and ultimately ends up as part of both the L and R signals. How do I do this?