Class AB Audio Power Amplifier Schematic Circuit Diagram

A Class AB Audio Power Amplifier represents an amplifier configuration that falls between the characteristics of Class A and Class B configurations. It incorporates a minor diode biasing voltage to ensure that the output transistors remain active, even in the absence of an input signal. Consequently, these transistors operate within their active region for small input signals, effectively preventing crossover distortion. In simpler terms, during more than one half-cycle of the input signal, one transistor remains ON.

This configuration effectively eliminates crossover distortion while maintaining a relatively insignificant collector current during idle conditions, which is notably lower when compared to the Class A configuration. Below, you’ll find a straightforward, high-quality audio power amplifier designed to operate with a 12V DC power source. Such an amplifier proves exceptionally suitable for car audio applications, given its uncomplicated design and the use of readily available components. Its power output typically hovers around 10W.

Description

This circuit relies exclusively on transistors for its operation. The initial stage of the circuit features a long-tailed pair (LTP) constructed using transistors Q1 and Q2. Transistors Q10 and Q11, along with their associated components, establish a constant current source for this long-tailed pair. Biasing in this stage is achieved through the use of resistors R15 and R3.

Moving to the second stage of the circuit, it centers around transistor Q3. Here, transistors Q9 and Q6 work in tandem to create a constant current source for the second stage. Resistor R8 serves as the feedback resistor, a crucial element in reducing distortion.

The ultimate stage of power amplification within the circuit relies on complementary pairs, specifically Q8 and Q5. Q7 and Q4 function as the driver transistors for Q8 and Q5, respectively. The audio output is transmitted to the loudspeaker by way of capacitor C3. Biasing diodes D1 and D2 are also present in the circuit. Additionally, C4 functions as the power supply filter capacitor. It’s important to note that this amplifier circuit can be effectively powered within a voltage range spanning from 12 to 16 volts.

Circuit diagram

Notes.

• Use 12V DC for powering the amplifier.
• An optional 10K POT can be added in series to the input for volume control.
• Use a 4 ohm/20W speaker as the load.
• Transistors Q8 and Q5 must be fitted to a proper sink.