5 Watt Class-A Audio Amplifier: Build Your Dream Circuit

Description

This solid-state push-pull single-ended Class A circuit demonstrates audio performance akin to that of valve amplifiers, delivering an output power of 6.9W when measured across an 8 Ohm loudspeaker system. The design offers reduced Total Harmonic Distortion, elevated input sensitivity, and improved linearity. The voltage demanded by the circuit is 24V, while the current draw reaches 700mA – a considerable reduction compared to the 250V HT rail and 1A @ 6.3V filament heating commonly found in valve-based amplifiers. The primary disadvantage of utilizing transistors within this circuit lies in the need for a substantial Heatsink for components Q2 and Q3 (the minimum dimensions of the required heatsink are 120x50x25mm). Nevertheless, the heat generated by this design can rival that of a single valve amplifier. The incorporation of a bass-boost function is possible through the utilization of components R5 and C5.

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Integrated Circuits (ICs) Details

The core of this circuit relies on three bipolar junction transistors (BJTs): BC560, BD439, and BD439. These transistors act as the amplification elements within the push-pull single-ended Class A amplifier configuration. The BC560, being a general-purpose NPN transistor, serves primarily as the input transistor, handling the initial signal amplification. The BD439 transistors are utilized as the output transistors, delivering the amplified signal to the loudspeaker. These transistors require adequate heat dissipation, necessitating the use of a suitably sized heatsink to maintain their operating temperature within safe limits. The selection of these specific transistor models contributes to the overall performance characteristics of the amplifier, particularly concerning linearity and distortion reduction.

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