A low power audio amplifier that can provide power up to 250mW can be designed using electronic diagram below.
Electronic scheme is simple and is built with transistors and common electronic components.
A BC547 transistor drive a balanced power amplifier made with BC337 and BC327.
Idle current is set by the diodes D1 and D2. Due to simplicity of circuit, the rest current varies with temperature.
Amplification is determined by the values of R1 and R3 and, P1 potentiometer. With values indicated in the scheme, and depending on the setting of P1, the amplification is about 15 and can be modified by changing the value of R1.
Input sensitivity, corresponding to a power output of 250 mW and an 8-ohm amplification 15, is about 95 mV, consumption current is about 180 mA.