[kipman725]

Hello are there any scematics around for low power class D amplifiers? all the amps I see are 400w sub amps etc.

Also does anyone know of mosfets with lower than 40pF gate capacitance?

 

[tin ears]

Good question.

A class d headphone amp design would be perfect for low/no heat and low power draw portable HP amps. Moreover, if the physical size scales well, the thing could be very tiny. Even smaller than the current altoids and more powerful and more efficient, with longer battery life.

In fact, I would bet this could be the only practical amp design to use in a fully active headphone. One in which the amp was directly wired to the transducer within the can itself, and optimized for that transducer, similar to active speaker designs.Implemented properly, with SOTA materials, it could be the ultimate HP.

Imagine a HP amp adequately powered by a watch battery or two that lasts for a month or more.

 

[balou]

I don't think that class D has enough benefits in already low-power headphone applications - but ymmv. And do you mean class D with commercial off-the-shelf amplifier chips, or everything built from scratch? You could find circuits for the former in any datasheet for low power amps, the latter would be a bit more complicated, see http://sound.westhost.com/articles/pwm.htm for a good intro.

Btw, Analog Devices and TI both have class d amplifier chips

 

[Log1c]

The hardest part about working with class D stuff is that most of it is of crappy quality or they are in a package that does not lend itself to prototyping well. (ie bga, tqfp)

I've used the TPA2000 chip before as it is a TSSOP package. (ti.com)

 

[kipman725]

it would be a from scratch design not using prebuilt moduals or class D amplifiers on a chip. I have already read the esp artical on the subject which is what gave me an interest. My a level electronics project includes many ideas from class d amplifiers (basicly putting in a pic the post PWM stage so that I can do all sorts of weird distortions on the sound (nothing fancy more like variable static). Obviously a real amp wouldn't want this middle stage.

So far I have designed a 2nd order butterworth lowpass VCVS filter for atenuation of frequancys above 40khz on the input.

anyway I should have worked everything out in a few months so I will see if it's viable while tinkering with this project (which dosen't have to have nice sound quality - only work (and can have a class ab output if rearly needed)).