'Loudmouth' Class C 12V power amplifier
Although not intended for 'hi-fi' applications this portable design was capable of pulling a fair punch with excellent intelligibility for speech applications and music.
To reduce crossover distortion, an HF astable running at 30kHz helped to average and thus fill-in the transition period. To maximise power output, the speaker was fed by two output stages, each anti-phase to the other and a transformer winding across the output was used to give a back EMF 'kick' of 24V across the load. Efficiency at maximum output is about 55%.
If, for higher outputs, 40411 output transistors were not available, other 30A types like the 2N3772 could be used instead. Upgrading the transformer secondary is also recommended. Compare to Class D operation.
These were used very successfully with a LM381 preamp and a Technics SL-10 driving a quantity of various speaker types including a Bessell array, sometimes in the remotest of sites. For safety, fuse to suit load. An automotive bulb can be ideal.
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