I want to build a simple audio mixer (adder) (from stereo line inputs) of good quality and low energy consumption. I found this simple design:
and I also found this one that also uses a transistor:
Q1: would the simple design work well, or is it just a theoretical example? Otherwise, why would the second design add a transistor? (Q2)
The second design's webpage says: "If two of these circuits are made in the same enclosure for stereo, then there can be a single power supply to run both of them. There should be a resistor in series with the incoming 9V+ lead so as to minimize crosstalk, and reduce the PLOP when it's powered on."
Q3: How big should this resistor be (Ohm)? Q4: So each of the two stereo's mixers circuits should have their own resistor in series with / connecting to the battery?
Q5: The second design uses a lot more power because the transistor draws a current while it's not used. Battery power wouldn't be feasible, right?