18W Audio Amplifier

-- 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 = 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

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.

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