30 Watt Audio Amplifier Schematic: A Powerful Build!

Description

This project involved designing an audio amplifier capable of delivering a respectable output power with a minimal component count, while maintaining quality. The Power Amplifier section utilized only three transistors and a handful of resistors and capacitors in a shunt feedback configuration, yet it was capable of delivering more than 18W into an 8 Ohm load with 0.08% THD @ 1KHz at the onset of clipping (0.04% @ 1W - 1KHz and 0.02% @ 1W - 10KHz) and up to 30W into a 4 Ohm load.

To achieve such performance and to ensure overall stability of this simplified circuitry, a suitably regulated DC power supply was indispensable. This was not a concern, as it also helped in minimizing the noise and hum of the preamp to very low levels and guaranteed a predictable output power into varying load impedances. Finally, given that the amplifier required a single rail supply, a robust DC voltage regulator capable of supplying more than 2 Amps @ 40V could be implemented with a limited number of components as well.

The BC550C transistor was selected for its low noise and high gain characteristics, while the IRF530 and IRF9530 provided significant current handling capability for the output stage. These components were mounted on appropriate heat sinks to dissipate the heat generated during operation. The use of these transistors along with the configuration allowed for a power output exceeding the design goals.

The BC550C, 2N3819, and BC550C transistors in the preamp section were chosen for their general-purpose characteristics and suitability for this application. The preamp was designed for maximum sensitivity and a wide overload margin, particularly important for modern music sources like CD players, tape recorders, iPods, and computer audio outputs. The volume control was strategically placed at the preamp input to further enhance the overload margin.

After a unity-gain impedance converter stage (using a BC550C), a Baxandall-type bass and treble tone control stage was added. This stage, required to provide a gain of approximately 5.6 times, employed a low-noise, “bootstrapped” two-transistor circuit with FET-input. This design included excellent THD figures up to 4V RMS output and a low output impedance, necessary for driving properly the Mini-MosFet Power Amplifier, but could also be utilized for other purposes. This approach utilized FET transistors to optimize performance and minimize distortion.

Circuit diagram:

Power Amplifier Parts:

Circuit diagram:

Power Amplifier Parts:

Notes:

Technical data: