Home Projects Audio 18W Audio Amplifier



18W Audio Amplifier

source: RED Free Circuit Designs
 -- High Quality very simple unit
 -- No need for a preamplifier


Circuit diagram:

18 Watt Amplifier

Amplifier parts:

P1 = 22K Log.Potentiometer (Dual-gang for stereo)
R1 = 1K 1/4W Resistor
R2 = 4K7 1/4W Resistor
R3 = 100R 1/4W Resistor
R4 = 4K7 1/4W Resistor
R5 = 82K 1/4W Resistor
R6 = 10R 1/2W Resistor
R7 = R22 4W Resistor (wirewound)
R8 = 1K 1/2W Trimmer Cermet (optional)
C1 = 470nF 63V Polyester Capacitor
C2,C5 = 100F 3V Tantalum bead Capacitors
C3,C4 = 470F 25V Electrolytic Capacitors
C6 = 100nF 63V Polyester Capacitor
D1 = 1N4148 75V 150mA Diode
IC1 = TLE2141C Low noise,high voltage,high slew-rate Op-amp
Q1 = BC182 50V 100mA NPN Transistor
Q2 = BC212 50V 100mA PNP Transistor
Q3 = TIP42A 60V 6A    PNP Transistor
Q4 = TIP41A 60V 6A    NPN Transistor
J1 RCA  audio input socket

Power supply parts:

R9 = 2K2 1/4W Resistor
C7,C8 = 4700F 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 switch



  • 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.

Technical data:

Output power: 18 Watt RMS @ 8 Ohm (1KHz sinewave)

Sensitivity: 150mV input for 18W output

Frequency response: 30Hz to 20KHz -1dB

Total harmonic distortion @ 1KHz:  0.1W 0.02%    1W 0.01%    5W 0.01%   10W 0.03%
Total harmonic distortion @10KHz: 0.1W 0.04%    1W 0.05%    5W 0.06%   10W 0.15%

Unconditionally stable on capacitive loads




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