Z1 can be a 100 ohms or higher head phone.I used 12V DC for powering the circuit.Power supply can be anything between 6 to 24V DC.The circuit can be assembled on a vero/perf board.Output of the amplifier is coupled to the head phone using the capacitor C3. C4 and C5 are power supply filter capacitors. Resistor R5 limits the collector current of Q2 and Q3. Base of Q3 is directly coupled to the collector of Q1. Diodes D1 and D2 provides bias voltage for Q2. Emitter of Q1 is coupled to the base of Q2 through resistor R3. Audio input is coupled to the base od Q1 through capacitor C2, resistor R9 and POT R10. Resistors R6 and R7 provides potential divider biasing for Q1. In the circuit transistor Q1 works as the preamplifier. These amplifiers are most suitable for low power applications. But the advantages of Class AB amplifier are no cross over distortion, high fidelity and low harmonic distortion. The maximum possible efficiency for Class A operation is 50% and it further reduces when capacitive coupling is used. In class A mode the output device (transistors) conduct over the entire input signal cycle. This is the circuit diagram of a Headphone amplifier operating in the class A push pull mode.
The circuit can be assembled on a vero board.Circuit diagram of 4 transistor amplifier. C5 and C6 are power supply filter capacitors. The output of the amplifier is coupled to the loud speaker through the capacitor C4. Diodes D1 and D2 provides the bias voltage for the push pull stage. Resistor R8 limits the collector current of Q2.The third stage is the class AB push pull section comprising of transistors Q3 and Q4. This stage is also collector to base biased and its input is coupled to the output of the preamplifier stage using capacitor C2. Q2 with its associated components perform this job.
TRANSISTOR AMPLIFIER DRIVER
The second stage is the driver stage for the push pull pair. Collector to base biasing is a good method of biasing for circuits like this as it provides enough negative feedback, prevents thermal runway and stabilizes the operating point. Resistor R3 provides collector to base bias for Q1 and C3 is an AC by pass capacitor for the collector resistor R4. The audio input is coupled to the base of Q1 through resistor R1 and capacitor C1. Transistor Q1 with its associated components is wired as a pre amplifier stage. The circuit shown here is suitable for small radio receivers, audio players, intercom, telephone etc. Up to 78% efficiency is possible with class AB designs and cross over distortion is reduced. In class AB operation each output device conducts more than half of the input signal cycle. Description.Ī very simple and easy to build class AB audio amplifier using four transistors is shown here. More over the value of the components are not very critical and slight variations in it will not affect the performance. The main feature of these circuits is that they all are just basic designs and the components used can be easily obtained from your junk box. These are circuits that can be used in a lot of low scale applications. A Low cost amplifier circuit using Transistor So you may keep visiting this post in future for more updates. This article is solely dedicated to publish more transistor amplifier circuits. This article is a list of various types of amplifier circuits built using Transistors alone.This includes a Class AB amplifier using 4 transistors, then we have a headphone amplifier circuit and finally a low power amplifier using transistor.
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