Okay, maybe I have connected something incorrectly then...
Before I continue, could anyone tell me what range of voltage and current is to be expected from a line-level and/or headphone signal?
(I'd like to try setting up my circuit in a simulator before risking frying another micro controller.)
Edit1:
Can't seem to get it to work in the simulator:
Circuit design Arduino Line-Level sound level input | Tinkercad
I only get 0.