This is the circuit of Op-AmpMicrophone Preamplifier using a single power supply, this circuit suitable for dynamic or electret microphones. Nothing too special here. The Schematic is shown using a dynamic microphone, for use with an electret a pair of suitable biasing resistor is required to power the electret microphone. Note: use a capacitor with voltage 25volt or more so that the sound produced maximal use supplay good voltage, with output of 18 volts max If the desired strengthening of the different, you can change the value of R1 or R2 The design is a standard non-inverting design, the input is applied to the non-inverting input of the op-amp, which is pin 3 in most cases. The input impedance is 23.5k, the overall voltage gain is determined by R2 and R1according to the following formula: Vo = (R2 / R1) + 1 With the values of R2 and R1 on the diagram of the voltage gain (for mid band, 1kHz) is approximately 23x or 27.2dB.