I assume, that you understand, that a passive mixer creates crosstalk with non-zero source impedance. An active mixer however shouldn't. Otherwise it's not working correctly. Details can be determined by real measurements.
I understand that in theory, an active mixer creates a "canceling" current that prevents crosstalk, but I don't understand it at the electron flow level.
According to the referred link (
**broken link removed**) the purpose of an active mixer is to prevent crosstalk through this "Virtual Earth" zone. It summarizes earlier that within passive mixers there is the possibility of crosstalk. The article, however, does not go into the details of what the crosstalk is? What are its characteristics? Why does it matter?
I apparently don't fully understand because I don't see how the three mixing inputs (in their example) can affect each other in such a way that they would degrade the final output product.
I was able to do a bit of experimenting this weekend to ensure that my connections were clean. In addition, I retested my Amplifer IC without the Op-Amp and found that everything operates perfectly. With my setup as follows:
Op-amp1 -- Input1 --{Amplifier1
Op-amp2 -- Input2 --{Amplifier1
I found that as long as I did NOT connect BOTH op-amps into the circuit I had no crosstalk, whether none or one. When both op-amps were connected the same crosstalk that occurred in the last test setups returned (channel 1 bleeding into speaker 2, sound distorted). Be mindful that this is a dual Op-Amp chip and at the time of the experiment it was grounded and fed with power. This just leads me to experiment (when I have time) with just the op-amp to verify that...
a.) I'm employing it properly
b.) the chip has not been damaged
c.) the feeding power is acceptable
I suppose if anyone has any additional articles that you could refer me to I would appreciate it. Through having a better understanding of the principles of active mixers I may come to acknowledge that this is the solution to mixing three input channels into two outputs. As for now, my ignorance tells me that active mixing is not the right solution or the op-amp chip is not working.