Most simple circuit:
1.5 volt alkaline, two 2.43K 1% current limiting resistors, two ~2.2 to 5 MFD 25-35 volt capacitors with - negative terminal the output of the channel.
Connect the + of battery to both resistors, and other end of each resistor is left/right channels connected to + of MIC, mentioned end of resistor, and + of capacitor.
Everything else not mentioned is common ground connected for both input, - battery, and output.