18W Audio Amplifier
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 |
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
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