Here is the circuit diagram of a simple dynamic microphone amplifier using two transistors. The amplification factor of this circuit is around 150 and can handle signals from 50Hz to 100Khz.These features make it ideal for audio applications. The audio signal from the microphone is coupled to the base of Q1 via the capacitor C1 and resistor R3. Q1 works as a preamplifier here. The preamplified signal will be coupled to the base of Q2 for further amplification. Resistor network comprising of R4, R5 and R6 provides the necessary negative feedback. Final output signal will be available at the emitter of Q2.
- The circuit can be assembled on a vero board.
- Use 12V DC powering the circuit.
- This circuit is designed for use with 200 Ohm dynamic microphones. For usage with low impedance microphones, the value of R3 must be increased to around 47o Ohms and C1 must be decreased to around 2.2uF.
- The circuit can be also operated from a 9V PP3 battery with a little compromise on performance.