Simple Audio Amplifier

This is an audio amplifier circuit which has power of 18W. It is very simple but it has a high quality. This circuit does not require pre amplifier. It can be directly connected to tuners, tape recorders, and CD players. It produces 18 Watt RMS into 8 Ohm (1KHz sine wave) output.this circuit has a good sensitivity,  for 18W output it need 150mV input. Furthermore this circuit has low distortion at 1KHZ and 10KHZ. Here is the circuit :

In this circuit a quiescent current (best measured with an Avo-meter in series with Q3 Emitter) is not critical. We can add R8 (optional) to facilitate quiescent current setting. D1 should be in thermal contact with Q1. Q4 and Q3 should be assembled on heatsink. To read a current between 20 to 30 mA without input signal we can adjust R3. A correct grounding is very important to eliminate ground and hum loops. Connect to the same point the ground sides of P1, J1,  C3, C4, & C2. Connect C6 to the output ground. Then connect separately the output and input grounds to the power supply ground. To prevent damage to the circuit, do not exceed 23 + 23V supply. [Schematic diagram source:  redcircuits.com]