This is the circuit diagram of mic condenser amplifier. The low-cost and compact mic condenser audio amplifier described right here is deliver good-quality audio of 0.5 watts at 4.5 volts. It could possibly be applied as a part of low-power transmitters, packet radio receivers, intercoms and walkie-talkies.

Transistors T1 and T2 form the mic preamplifier. Resistor R1 gives the required bias for the mic condenser whilst preset VR1 works as gain control for adjusting its gain level. As a way to boost the audio power, the low-level audio output from the preamplifier stage is coupled via coupling capacitor C7 to the audio power amplifier constructed close to BEL1895 IC.

BEL1895 is really a monolithic audio power amplifier IC intended specifically for sensitive AM radio applications that delivers 1 watt into 4 ohms at 6V power supply voltage. It exhibits very low distortion and noise and works above 3V-9V supply voltage, which would make it perfect to be supplied with battery operation. A turn-on pop reduction circuit prevents thud once the power supply is switched on.

Coupling capacitor C7 determines low-frequency response of the amplifier. Capacitor C9 acts as the ripple-rejection filter. Capacitor C13 couples the output accessible at pin 1 towards the loudspeaker. R15-C13 combination acts as the damping circuit for output oscillations. Capacitor C12 presents the boot strapping function.

This circuit is appropriate for low power HAM radio transmitters to supply the important audio power for modulation. With easy modifications it could possibly also be applied to intercom circuits.

Mic condenser amplifier circuit source: “Electronics For You” magazine, December 2001