This Audio amplifier has output 18 Watt RMS into 8 Ohm (1KHz sine wave) and Frequency response 30Hz to 20KHz -1dB. It’s simple to build and you don’t need preamplifier. Few notes about this circuit.

• Do not exceed 23 + 23V supply.
• Can be directly connected to CD players, tuners and tape recorders.
• D1 must be in thermal contact with Q1.
• Quiescent current (best measured with an Avo-meter in series with Q3 Emitter) is not critical.
• Q3 and Q4 must be mounted on heatsink.
• To facilitate quiescent current setting add R8 (optional).
• Adjust R3 to read a current between 20 to 30 mA with no input signal.
• 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.

Circuit 18W Audio 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_________100µF 3V Tantalum bead Capacitors
C3,C4_________470µF 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________4700µF 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

source : http://www.redcircuits.com//Page1.htm