50mW Transistor Audio Amp Circuit Diagram

Description

A compact audio amplifier, resembling those found in small portable radios, is presented here. The input stage is configured to evenly distribute the power supply voltage across the paired, complementary output transistors, utilizing diodes placed between their bases for slight current conduction enhancement. A 3.3 ohm resistor is implemented in series with the emitters of the output transistors to maintain a stable bias current, minimizing variations due to temperature fluctuations or differing transistor and diode characteristics. As the bias current rises, the voltage between the emitter and base is reduced, consequently decreasing conduction. The input impedance is approximately 500 ohms, while the voltage gain achieves around 5 when coupled with an 8 ohm speaker. The amplitude of the signal on the speaker is approximately 2 volts without causing distortion, and the power output is within the 50 milliwatt range. Increased supply voltage and the incorporation of heat sinks onto the output transistors would yield greater power capabilities. This circuit draws approximately 30 milliamps from a 9 volt power source.

Circuit diagram