I bought a bargain external speaker and mic for an iPOD. I wanted to play a tape recorder device direct into the speaker by plugging the speaker + mic into the 3.5mm (1/8 inch) output of a tape recorder.
It wouldn't work even when changed some of the connections after I had checked the pinout for the four connectors on the 3.5mm plug and
When I opened up the external speaker + mic there was circuit board. What does the circuit board do?