Updated Jan 10. 2007

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DIY Self Oscillating Class-D Amplifier (SODA)

I have for a long time worked on different class-d amplifiers on a breadboard, and have now settled for a solution based on self oscillation, and using a HIP4080A as MosFet bridge driver. The MosFets I'm using are the well known IRF640. These seems to work well and are dirt cheap. This article is divided into parts or stages, to give you an idea of the design evolution. Starting from the very first bread board tryout to finalized  double sided PCB based on SMD components.

This amp is intended as an amp for my subwoofer project, where I'm using a 12" Peerless XLS driver. I want in the region of 400 W to drive it fully, and I hope this design will be able to deliver that.

This article is meant as an inspiration for others working on similar projects, and not a description on how you can or should do yourself. I think class-d amplifiers are a real challenge, this project has taken countless hours in research and development. It requires real good insight in electronics and the art of PCB layout.

A word of advise: don't do a full bridge (H-bridge) as the first project! Though this kind of design offers a lot of benefits over a half bridge design (no PSU pumping, single sided PSU), it tends to get quite a lot more complex and hard to get to work properly.

Another advise: Do start with a breadboard ..... it will save you hundreds of hours. You should definitely use simulation programs like spice, but these models are not reality, and especially not in the case of class-d amplifiers. Breadboards will enable you to change components almost on the fly, at will help identify the most critical parts of the circuit.

Enjoy reading the next pages:

Breadboard Prototype I Prototype 2
This is how it all started The first PCB. It ended up quite good, but I had some troubles with noise, which requires some changes. 2. Prototype has been implemented. All the important circuits work, and the sound is excellent. This will be the final version, which will go into the XLS subwoofer.