About The Circuit
This three transistor audio amplifier has been designed so as to deliver almost 100mW power to a 25 Ohm speaker. This circuit can easily be assembled on a vero board with a 9 Volt PP3 battery to provide the power. In the circuit the special notice should be given to the capacitors C1 and C2. They must be rated a minium of 15Volts.
The transistors Q1 and Q2 are provided with a constant bias voltage with the help of diodes D1 and D1. Out of these transistors Q1 acts as a pre-amplifier and Q2 and Q3 are used to drive the speaker. There is no necessity regarding the type number of the transistors. All you have to notice is whether Q1 and Q3 are NPN transistors and Q2 is a PNP transistor. In the case of the transistors the minimum collector current capacity should not be less than 100mA. Even if the speaker resistance is reduced to 8 Ohms, the circuit will work, but with lesser volume.