Headphone Amplifier(Class A)

Description.

This is the circuit diagram of a Headphone amplifier operating in the class A push pull mode. In class A mode the output device (transistors) conduct over the entire input signal cycle. The maximum possible efficiency for Class A operation is 50% and it further reduces when capacitive coupling is used. But the advantages of Class AB amplifier are no cross over distortion, high fidelity and low harmonic distortion. These amplifiers are most suitable for low power applications.

In the circuit transistor Q1 works as the preamplifier. Resistors R6 and R7 provides potential divider biasing for Q1. Audio input is coupled to the base od Q1 through capacitor C2, resistor R9 and POT R10. Emitter of Q1 is coupled to the base of Q2 through resistor R3. Diodes D1 and D2 provides bias voltage for Q2. Base of Q3 is directly coupled to the collector of Q1. Resistor R5 limits the collector current of Q2 and Q3. C4 and C5 are power supply filter capacitors. Output of the amplifier is coupled to the head phone using the capacitor C3.

NOTES:

• The circuit can be assembled on a vero/perf board.
• Power supply can be anything between 6 to 24V DC.
• I used 12V DC for powering the circuit.
• Z1 can be a 100 ohms or higher head phone.
• Electrolytic capacitors voltage rating must be according to the supply voltage you use.