18W Audio Amplifier

This is the circuit diagram of 18W audio amplifier. The circuit is quite simple and inexpensive to built. It uses a pair of power transistor TIP41A and TIP42A for single channel operation. The power supply used for this circuit is dual polarity (splitted) power supply, use center tap transformer to build this kind of power supply.

Parts list:

Power supply parts:

R9 = 2K2	1/4W Resistor
C7,C8 = 4700?F	25V Electrolytic Capacitors
D2	100V 4A Diode bridge
D3	5mm. Red LED
T1	220V Primary, 15 + 15V Secondary 50VA Mains transformer
PL1	Male Mains plug
SW1	SPST Mains switc

18W Audio Amplifier Circuit Notes:

• Can be directly connected to CD players, tuners and tape recorders.
• Don’t exceed 23 + 23V supply.
• Q3 and Q4 must be mounted on heatsink.
• D1 must be in thermal contact with Q1.
• Quiescent current (best measured with an Avo-meter in series with Q3 Emitter) is not critical.
• Adjust R3 to read a current between 20 to 30 mA with no input signal.
• To facilitate current setting add R8 (optional).
• A correct grounding is very important to eliminate hum and ground loops. Connect in the same point the ground sides of J1, P1, C2, C3 &C4. Connect C6 at the output ground.
• Then connect separately the input and output grounds at the power supply ground.