Many times we want a circuit which will fit in less space and run from low power so this is a circuit of your choice there are many circuits of 1watt audio amplifiers which use ICs in there circuits but this circuit use only four transistors to make a good and useful out put power of more then 1.3
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watt and also run with a handy power supply which is 9 volt. All transistors which used in this circuit are dc coupled which make the circuit simple may be the adjustment of the circuit will difficult but by proper understanding the working of circuit and then adjusting for right voltage and current will over come this difficulty. Transistor Q1 BC 148 Q3 and Q4 in series are making class B amplifier Q2 AC 132 is operating at 10mA to giving sufficient drive. The R10 resister is providing temperature stabilization to transistor Q3 AC 188 and Q4 AC 187. The transistor Q3 and Q4 should be mounted on heat sink. To adjust this circuit short the resistors R8 and R10 and select a value of resistor R2 to give 4.5 volts at "A" with respect to ground. After this attach meter in series of battery to check current. The meter should show 10mA. Remove the short adjust R8 till the meter shows 15mA. Use some glue or any other material to seal Resistor R8 to this point. If you increasing quiescent current this will reduce the distortion more but it will increase the consumption of battery power. But 5mA quiescent current is a good compromise. The amplifiers input impedance is 30 K ohms; response of frequency extends up to 30 KHz. 25 mV signal will give full power output.
