18W Audio Amplifier

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High Quality very simple unit

No need for a preamplifier

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Circuit diagram:

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

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Notes:

• Can be directly connected to CD players, tuners and tape recorders.
• Do not 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 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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Technical data:

Output power:

18 Watt RMS into 8 Ohm (1KHz sine wave)

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