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.18W Audio Amplifier

18W Audio Amplifier Circuit Diagram

Parts list:

P1 = 22KLog.Potentiometer (Dual-gang for stereo)R1 = 1K1/4W ResistorR2 = 4K71/4W ResistorR3 = 100R1/4W ResistorR4 = 4K71/4W ResistorR5 = 82K1/4W ResistorR6 = 10R1/2W ResistorR7 = R224W Resistor (wirewound)R8 = 1K1/2W Trimmer Cermet (optional)C1 = 470nF63V Polyester CapacitorC2,C5 = 100?F3V Tantalum bead CapacitorsC3,C4 = 470?F25V Electrolytic CapacitorsC6 = 100nF63V Polyester CapacitorD1 = 1N414875V 150mA DiodeIC1 = TLE2141CLow noise,high voltage,high slew-rate Op-ampQ1 = BC18250V 100mA NPN TransistorQ2 = BC21250V 100mA PNP TransistorQ3 = TIP42A60V 6A PNP TransistorQ4 = TIP41A60V 6A NPN TransistorJ1RCA audio input socket

Power supply parts:

R9 = 2K21/4W ResistorC7,C8 = 4700?F25V Electrolytic CapacitorsD2100V 4A Diode bridgeD35mm. Red LEDT1220V Primary, 15 + 15V Secondary 50VA Mains transformerPL1Male Mains plugSW1SPST 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.

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