18W Audio Amplifier | Schematic Diagrams

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18W Audio Amplifier


This circuit diagram is quite simple and cheap…

18W Audio Amplifier circuit

Amplifier parts:

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


  • 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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