Switched it and here's the hum-free circuit. This is why I used a breadboard to mock things up. Using the same DIN8 cable assemblies from Digikey, the orange wire is audio signal ground and the brown wire is +12V. When either the cassette player or radio is on, either component supplies power to the preamp section and EQ via the DIN8 cable. One more thing, the power antenna is controlled via the on-off push-button volume control, even if a tape is playing. The cassette player will still run whet