With the circuit shown, we have an excellent level for the signal obtained from an electret microphone. The LM324 amplifier must be supplied with voltages between 6 and 12 V. The resistor in series with the electret microphone depends on the supply voltage. The 33 nF capacitor can be increased to obtain a better response to bass sounds. Both the signal inputs and outputs of this circuit must be made with shielded wires, avoiding the capture of humming. The 120k ohm resistor determines the gain of the circuit and can eventually be changed or even replaced by a potentiometer.
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