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Topic: Cheap PWM amplifier for loudspeakers based on 74AC14 (Read 2238 times) previous topic - next topic


I developed a cheap class-D amplifier for PWM outputs to direct drive a speaker of 4 ohms or more. It is based on a 74AC14 which contains 6 inverting schmitt-triggers. The AC variant allows very high output currents, more than most other families. It is available at around ~0,30 EUR here in Germany. The amp give good volume, much more than what is possible from the Arduino ports directly. A bipolar electrolyte capacitor should be used to protect speakers from DC, I used a unipolar one, but that is not recommended. The coils are optional and just needed for RF reject on longer speaker cables that act as radio at such high slew rates. Any coil with about 100┬ÁH that can handle about 0.2A will do.

The circuit does not contain a low-pass filter and is therefore for PWM rates in the non-hearable region. Some noise on low volume parts of music can be noticed due 8-bit output. This circuit can also be used with SimpleSDAudio library.



here the same for stereo output with 16-bit, therefore much less audible noise when use with SimpleSDAudio in 16-Bit mode (need Mega-Arduino for stereo!). Works pretty well, albeit a little bit less volume than the mono version, but still loud enough for many applications. Trim poti to lowest noise (somewhere around 1k for 8 Ohm speakers).
You can use the SimpleSDAudio test file cali16b.bhs that contains a special tone that should be vanish if the poti is trimmed correctly.

Have fun,

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