Condenser Microphone Amplifier Schematic using BEL 1895 IC

Here I will show you an audio amplifier circuit that can be used for walkie talkies, low power transmitters, and packet radio receivers. A condenser mic audio amplifier gives good quality audio of 0.5 watts at 3 volts. Here we are going to make use of BEL 1895 (Bharat Electronics Limited 1895) audio amplifier IC which is also a noise free amplifier IC. We are also using a pre amplifier section here to boost the weak signal from condenser mic. The pre amplified signal is connected to BEL 1895 audio amplifier IC. The preset in the first transistor acts as a gain controller, it can vary the gain of amplifier circuit. PCB layout is also given below.

Circuit diagram

Click on the image for enlarged view.

Components required

Condenser mic
Speaker
BEL 1895 IC
Resistors (2.2kΩ, 470kΩ x2, 470Ω x2, 47kΩ, 33Ω, 1Ω, 1kΩ x2, 100kΩ, 220kΩ, 100Ωx2)
Preset 10kΩ
Capacitors (100µF x2, 0.1µF x3, 47µF, 10µF x3, 150µF, 470µF, 1nF x2, 33pF)

Working of BEL 1895 audio apmplifier

Transistors Q1 and Q2 form the condenser mic preamplifier. Resistor R1 provides the required bias for the condenser mic.

The 10KΩ preset at the emitter of Q1 functions as gain control for the voice signal.

In order to enlarge the audio power, the low level audio output from the preamplifier stage is coupled to the audio power amplifier BEL1895 IC via coupling capacitor C1.

BEL1895 exhibits low distortion and noise and operates over 3V-9V supply voltage, which makes it ideal for battery operation.

It is a monolithic audio power amplifier IC intended particularly for sensitive AM and FM radio applications.

Coupling capacitor C1 determines low frequency response of the amplifier. Capacitor C2 acts as the ripple rejection filter.

Capacitor C3 connects the output to the loudspeaker. R1-C4 arrangement acts as the damping circuit for output oscillations. Capacitor C5 provides the boot strapping function.