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Class D Amplifiers

HiFi, LoFi, Tubes, Transistors, ICs, Commercial, DIY

Postby melb » Sat Nov 30, 2013 12:00 am

I am interested in designing and building Class D Amps.
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Joined: Thu Jan 02, 2014 10:37 am

Postby inojim » Wed Dec 18, 2013 12:00 am

Hello, Mel.

Class D amps are becoming very popular because of their size and efficiency, and because contemporary ones are judged by many to sound as good as most linear power amps. A good understanding of Class D amps can be had by studying very early magazine articles. If you have access to back issues of the UK publication Wireless World, there was a series of articles by Messrs. Turnbull and Townsend back in 1965. I have fairly good scans of these articles, courtesy of Doug Self, and could make them available if anyone is interested and posts a reply to this effect.
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Joined: Thu Jan 02, 2014 10:37 am

Postby Guest » Tue Dec 31, 2013 12:00 am

The Class D Amp, in the Jan-Feb Issue of Elektor looks good. The 555 timer are used for the PWM. What I wonder is about the Clock frequency to reduce the intermodulation products which are a good -60dB. Could the Clock frequency be adjusted to say 220 kHz and 270 kHz to make the intermodulation a lot better. Yes the filters too would have to be adjusted accordingly. Has anyone tried this? How easy is it?

Postby johnhind » Sat Jan 04, 2014 12:00 am

Reading the Jan-Feb design, it occurred that it ought to be possible to modernize the whole Class D concept. I'm no audio designer, so it is not a project for me, but here are some ideas:

Use a four MOSFET full bridge to drive each loudspeaker. This avoids the need for the large output capacitor or a bi-polar power supply.

Use a boost converter to develop the loudspeaker drive voltage from a 5v (USB) DC logic supply. Control the drive voltage according to demanded gain and loudspeaker impedance to maximize the dynamic range of the amplifier.

Use the driver MOSFETS and/or the boost converter to implement protection and slow-start circuits avoiding the need for the electromagnetic relay.

Use a microcontroller for the modulation circuit and general control. Could maybe accept digital (TOSLINK / USB) inputs as well as analogue (preferably differential).
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Joined: Thu Jan 02, 2014 10:48 am

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