Audio Amplifier 100W or 130W
This audio amplifier delivers between 100 W and 130 W of output power, depending on the number of power transistors used in the output stage.
Output Stage Configuration
- Using 2 power transistors (2 × 2N3773), the amplifier produces approximately 90 W.
- Using 4 power transistors (4 × 2N3773), the amplifier delivers approximately 130 W.
- Driver transistors: BD137 (NPN) and BD138 (PNP) provide sufficient current and voltage gain to drive the output stage.
Power Supply
A symmetrical power supply is required to operate the push-pull output stage efficiently. Typical supply voltages are ±35V to ±40V, depending on the desired output power.
Construction Notes
- Mount all 2N3773 output transistors on a large heatsink with good thermal coupling to prevent overheating.
- Ensure proper biasing of the driver and output transistors to minimize crossover distortion.
- Keep input and feedback traces away from high-current output paths to avoid oscillations.
- Use adequately rated electrolytic capacitors in the power supply to reduce ripple at high power levels.
- Include fuses and protection circuitry in the power supply for safety.
Key Features
- Adjustable output power: 100 W (2 transistors) or 130 W (4 transistors)
- Complementary push-pull design
- Driver stage using BD137/BD138 for reliable current amplification
- Suitable for 4 Ω or 8 Ω speakers
PCB and layout
Use T3 on Heatsink
| Component | Ref./Value | Type |
|---|---|---|
| R1 | 120K | 1/4W Resistor |
| R2 | 3K3 | 1/2W Resistor |
| R3 | 5K6 | 1/4W Resistor |
| R4 | 3K3 | 1/4W Resistor |
| R5 | 680R | 1/4W Resistor |
| R6 | 120R | 1/4W Resistor |
| R7 | 3K3 | 1/4W Resistor |
| R8 | 1K2 | 1/4W Resistor |
| R9 | 2K7 | 1/4W Resistor |
| R10 | 1K5 | 1/4W Resistor |
| R11 | 680R | 1/4W Resistor |
| R12 | 120R | 1/4W Resistor |
| R13 | 120R | 1/4W Resistor |
| R14 | 0,33R | 5W Resistor |
| R15 | 0,33r | 5W Resistor |
| R16 | 10R | 1W Resistor |
| R17 | 10R | 1W Resistor |
| C1 | 10uF | 16V Electrolytic Capacitor |
| C2 | 330µF | 16V Electrolytic Capacitor |
| C3 | 470uF | 35V Electrolytic Capacitor |
| C4 | 150pF | Ceramic Capacitor |
| C5 | 100nF | 100V Polyester Capacitor |
| RV1 | 1K | Trimpot |
| D1 | 9V1 - 500mW | Zener |
| T1 | BC557 | PNP transistor |
| T2 | BC557 | PNP transistor |
| T3 | BC548 | NPN transistor |
| T4 | BD137 | NPN transistor |
| T5 | BD137 | NPN transistor |
| T6 | BD138 | PNP transistor |
| T7 | 2N3773 | NPN transistor |
| T8 | 2N3773 | NPN transistor |
| L1 | coil | largest number of turns rolled in R16 with AWG22 |
Power Supply
|
 |
| Component | Ref./Value | Type |
|---|---|---|
| T1 | 30+30 - 3,5A | Transformer |
| D1-D2-D3-D4 | Rectifier 5A - 150V | Diode |
| C1-C2 | 4700uF | 50V Electrolytic Capacitor |
| F1-F2 | 3A | Fuse |
| C3-C4 | 100nF | 100V Polyester |
Audio Output and Heatsink
4 transistors 130 W
