Class D amp

[Number04]

I am a relative audio noob, so mistakes will be present.

I am an Electronics Engineering student at SAIT in my 3ed semester and in 4th we have a final project that is basically a pass or fail thing.

Now, i know that i want to do any audio amplifier, and i have looked at allot of A/B MOSFET amps. While making a mid range hi-fi amp would be a great project, i started to look at Class D.

I took a look, and i could not find and schematics my self. I want to use digital on the input stage for voltage gain then use transistors with an AV of 1-0.9 for current gain on the final stage. I Have found some chips and what not, but i was wondering if anyone has experience building a class D in parts.

I do have a few months left for design and then 4 months for construction, so i am not yet pressed for time.

Any help would be great.

[Tieftoener]

Class D is rather difficult concept for a design class. I think you'd benefit more by doing a typical class A or A/B and comparing distortion by changing your feedback methods. Or by using different topologies (adding differential amplifier at input for example). Or perhaps developing your own type of biasing for Class-A amps... maybe something similar to Nelson Pass designs. Unfortunately, I learned the hard way not to tackly too much in a design project class...

Are you actually going to design something, or are you going to copy someone else's design?? (Curious as to why you want schematics...) Or did you just want to use them as a basis/reference? Quick thought to show learning comparisons for project: compare the efficiency of different output devices (pretty much a sure thing to be MOSFETs, but the turn on resistance greatly affects the efficiency of the switching device).

There is a great deal of design work to go into a class D amp... shilelding and filtering requirements are very intense (at least for a virgin designer). To make it easy for you... I did a quick search. EE times has an article here.

It covers a lot of Class D IC's... namely one on the bottom by Apogee. I did a once over on it, and it actually seems really neat! I'm actually thinking up a little DAC speaker project up using it now... the Apogee system uses some pretty advanced DSP algorithms and it allows you to run a full-bandwidth audio signal through it, out to 20kHz. Pretty impressive results from the Audio Precision plots in the datasheet as well. It's worth checking out... and perhaps starting a new thread for

Hope this gets you started - good luck!

[Number04]

The recommendation to the students by teachers was to find a schematic and modify it so to meet out needs. We will be putting the design into a simulation program, so change or edit anything.

Some of the chips look very strait forward.
sheet 1
sheet 2

Has anyone used anything like this at all? Any experience adding transistors for extra power?

Of course, the other way might be to build all the pulse width modulation circuits myself. Has anyone had any success with this? As you said Tieftoener, I don't want to be trying anything new, so I was hoping to stand on someone elses success.

[bknauss]

FYI - Class D is not a digital amp.

I would try one of the amp forums for better luck.

[phase_accurate]

FYI - Class D is not a digital amp.

Couldn't agree more !

Have a look at:

My very first Class D pwm (switching) amplifier.

Regards

Charles