The following diagram is mono 18W audio amplifier circuit. This transistored amplifier is powered by a couple of power transistor TIP41A and TIP42A. Build two similar circuit for stereo amplifier.
Amplifier Parts List:
P1 = 22K Log. Potentiometer (Dual-gang for stereo)
R1 = 1K 1/4W
R2 = 4K7 1/4W
R3 = 100R 1/4W
R4 = 4K7 1/4W
R5 = 82K 1/4W
R6 = 10R 1/2W
R7 = R22 4W Resistor (wirewound)
R8 = 1K 1/2W Trimmer Cermet (optional)
C1 = 470nF/63V Polyester Capacitor
C2,C5 = 100µF/3V Tantalum bead Capacitors
C3,C4 = 470µF/25V Electrolytic Capacitors
C6 = 100nF/63V Polyester Capacitor
D1 = 1N4148
IC1 = TLE2141C
Q1 = BC182
Q2 = BC212
Q3 = TIP42A
Q4 = TIP41A
J1 = RCA audio input socket
Power Supply Parts List:
R9 = 2K2 1/4W
C7,C8 = 4700µF 25V Electrolytic Capacitors
D2 = 100V 4A Diode bridge
D3 = 5mm. Red LED
T1 = 220V Primary, 15 + 15V Secondary, 3A
PL1 = Male Mains plug
SW1 = SPST Mains switch
Circuit Notes:
- The power supply do not exceed 23 + 23V supply, 15V transformer output is the recommended.
- Q3 and Q4 must use heatsink to prevent overheating.
- D1 must be in thermal contact with Q1.
- Adjust R3 to read a current between 20 to 30 mA with no input signal.
- To facilitate quiescent current setting add R8 (optional).
- A correct grounding is very important to eliminate hum and ground loops. Connect to the same point the ground sides of J1, P1, C2, C3 & C4. Connect C6 to the output ground.
- Then connect separately the input and output grounds to the power supply ground.
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