I have been hunting for some easy mixers to sum the 4 audio outputs since I dont have 4 channels free on my console and came across this: http://generalguitargadgets.com/diagrams/mixer_sc.gif Now my question is, what would be the most efficient way to power it from the C64 PSU? The ins and outs of the TL072 are a little over my head so i am not sure whats acceptable for supply voltages and how that impacts the audio