Power supply circuit diagram of 120W power amplifier

This is a schematic of a 120W power amplifier using TO-3 package complementary transistors, NPN and PNP polarities. The well-known power transistor pair 2N3055 and MJ2955 are used in this circuit. A +/- 50V symmetrical (split/bipolar) power supply with a minimum of 3A current should be used for best performance.

120W Power Amplifier Parts List

transistor

2N3055 (alternative: MJ15003 or 2N3772): 2

MJ2955 (replacement: MJ15004 or 2N3771): 2

Tip 42:2

Tip 41:1

2SC2229 or 2SC2230 or C1573: 2

A1015 or A872 or A733: 2

Capacitors

100uF/50V electrolytic capacitor: 2

470nF (474) non-polar polyester capacitor: 1

100pF (101) non-polar ceramic capacitor: 2

470pF (471) non-polar ceramic capacitor: 2

10pF non-polar ceramic capacitor: 2

100nF (104) 100V non-polar polyester capacitor: 2

Resistor

0.33Ω （ 5W）：4

10 Ω to (1W) – Brown, Black, Black: 1

100 Ω (1W) – Brown, Black, Brown: 2

33 Ω (1/4W) - Orange, Orange, Black: 1

150 Ω (1/4W) – Brown, Green, Brown: 3

10K Ω (1/4W) – Brown, Black, Orange: 1

1K Ω (1/4W) – Brown, Black, Red: 1

4.7K Ω (1W) – Yellow, Purple, Red: 1

68K Ω (1/4W) – Blue, Gray, Orange: 1

56K Ω (1/4W) – Green, Blue, Orange: 1

33K Ω (1/4W) – Orange, Orange, Orange: 1

3.3K Ω (1/4W) – Orange, Orange, Red: 2

diode

3A diode 1N5404: 2

1A diode 1N4007: 3

Zener diode between 20 and 24 volts: 1

other

3A fuse

Mini 3-pin (GP) connector

Large 6-pin connector (Molex)

Aluminum radiator

20K potentiometer if you want to add volume control

120W Power Amplifier PCB Layout Design

Bottom PCB layout (copper)

Top PCB layout and component placement

How to mount the transistor to the aluminum heat sink, see the picture below:

The main points are: protect the circuit from short circuits, use proper isolators and use thermal paste to maximize heat dissipation to the heat sink. Use mica between the transistor and the heat sink.

Power supply circuit of 120W power amplifier

Power supply bottom PCB layout

Power supply top PCB design

Power Supply Parts List

The transformer for a mono amplifier should be 35 + 35 VAC, at least 3 amps. For stereo channels, the amperage should be doubled.

4700 uF/63V Capacitor: 4

15 amp diode bridge (rectifier): 1

120W amplifier wiring

This is how to connect the amplifier module to the speakers, power supply and audio input. And connect the power supply module to the transformer.