They boost the signal enough to "drive" the heavy-duty 2N3055s.
A small-signal transistor (like a BC547 or 2N2222) acts as the initial pre-amp/differential pair. The BD139 and BD140 transistors form a complementary pair.
This stabilizes the gain and reduces total harmonic distortion (THD). Safety & Build Tips 2n3055 Audio Amp Schematic
potentiometer is usually placed here to adjust (to prevent crossover distortion). Output Stage (The 2N3055s)
The collectors of the 2N3055s are connected to the positive and negative power rails. They boost the signal enough to "drive" the
This design typically follows a push-pull architecture. It uses two 2N3055 transistors as the final power stage to drive an 8-ohm speaker. Key Components Power Transistors: 2x 2N3055 (NPN) Driver Transistors: BD139 (NPN) and BD140 (PNP) Voltage: Dual rail supply ( ±35Vplus or minus 35 cap V Power Output: ~50 Watts into 8 Ohms Step-by-Step Connection Logic Input Stage The audio signal enters through a electrolytic coupling capacitor.
Ensure your transformer is rated for at least 100VA for a mono build. This stabilizes the gain and reduces total harmonic
as these transistors generate significant heat during operation. emitter resistors to provide thermal stability. Feedback Loop A resistor (typically ) connects the output back to the input stage.