18W Audio Amplifier

source: RED Free Circuit Designs

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-- High Quality very simple unit

-- No need for a preamplifier

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 = 100΅F	3V Tantalum bead Capacitors
C3,C4 = 470΅F	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 = 4700΅F	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

from:: http://www.electronics-lab.com/projects/audio/012/index.html