Class-D amplifier conclusions

I’ve completed the last part of the amplifier project. The 20W stereo amplifier board i tested – and works like a charm!

I discovered an error in the layout of the input stage having connected the feedback resistor to the input instead of the feedback pin. whoops, no sound through the left channel. luckily it was a very quick fix with only one track cut and a rotated cap. job done – now the amp is playing along very nicely!

I should do some real power testing to confirm the efficiency claims but I haven’t got the time yet. Although I have some serious 4 and 8 ohm resistors laying arround (>300W power resistors). I might do that one day.

2014-03-30 20.43.36Just a nice quick picture for comparison. the weight? I should get a precision scale. The kitchen scale wont even register the small (10W). both combined is about 3g.. talk about a Power-to-Weight ratio that rocks!!



  1. Just one comment. Look in MAX9744 data sheet, the working range is 4.5-14V, but you only has a 3.3v reg. on your schematic. Just wonder if you should have at least a 5v reg?

    Just my 2cent, and good work BTW.

    • You’re right although you’re wrong 🙂
      The PVDD is 4.5 to 14V but the VDD is 3 to 3.6V. So the powerstage needs at least 4.5V but the control circuits lives on 3.3V. If you see on page 24 of the datasheet you can see the two power rails on top of the chip. Good catch 🙂 (and to be honest I did goof up the first version of the 10W amp. I put on a 5V regulator but luckily I haven’t had problems with them.

  2. Good to hear. Just wonder how loud it is with 5V?

    • Hi Ben, Sorry for not getting back to you before now. I’ll have a hard time quantifying the sound pressure at different voltages. I’d say that it’s pretty loud. I should do some tests with dummy loads but this isn’t very high on my list. I would have a close look at the datasheet and use the graphs and equations from there to find a better answer. and finally – the THD is also present when playing really loud.. just a reminder 🙂

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