18W Audio Power Amplifier Circuit
18W Audio Power Amplifier Circuit designing an audio amplifier capable of delivering a decent output power with a minimum parts count, without sacrificing quality. The Power Amplifier section employs only four transistors and a handful of resistors and capacitors in a shunt feedback configuration but can deliver more than 18W into 8 Ohm with 0.08% THD @ 1KHz at the onset of clipping (0.04% @ 1W – 1KHz and 0.02% @ 1W – 10KHz) and up to 30W into a 4 Ohm load
18W Audio Power Amplifier Circuit
To obtain such a performance and to ensure the overall stability of this very simple circuitry, a suitable regulated dc power supply is mandatory. This is not a snag because it also helps in keeping the noise and hum of the preamp to very low levels and guarantees a predictable output power into different load impedance.
Working of Power Amplifier Circuit
- This circuit Can be directly connected to CD players, tuners, and tape recorders.
- Do not exceed 23 + 23V supply.
- Q3 and Q4 must be mounted on the 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.
- Connect separately the input and output grounds to the power supply ground.
Components for 18W Audio Power Amplifier Circuit
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 Components
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
