About a simple class D amp

That is a really horrid design and for audio work it really isn't going to do at all. You may be able to understand a voice but it will be very hard to listen to.

You want the output to be push pull.

No way this schematics is going to make 100 to 300W.

The first improvement is use the half bridge output stage instead of the single ended.

If you need a simple class D amplifier which really works, there is a bunch of single IC solutions from TI, NXP, ST, Freescale. If this is about the minimalist contest, a class D amplifier can be built using just one FET and few resistors and caps.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

That sounds cute. How?

John

And that makes distortion OK ?

It's a heap of crap if that's what you wanted to know.

Go to I.R. ( irf.com) and use one of their application circuits.

Graham

Hello

Yes, a minimalist, any diagrams of that class D amp using one fet and few resistors and caps ?

Thank

Jean

Assuming you tolerate distortion, you can do it with one mosfet and no other parts.

John

Which puts net DC through the speaker and is *completely* inappropriate for a high power design.

Graham

A basic oscillator circuit with hipass RC-RC-RC in the feedback from drain to gate. The speaker is the load in the drain. The hint is that at high frequencies the speaker inductance makes the resonance with the FET stray capacitance. The typical parameters make the resonance exactly where it is needed. So, the whole thing oscillates in the nonlinear mode, and the FET is switching. If the audio frequency is applied to the gate, that pulse width modulates the drain current. There is also the bias circuit to keep the operating point.

As simple as that: FET, speaker, 4 resistors and 3 caps.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

Yikes! Sounds like a class AD amplifier!

You could do it with a fet and one TinyLogic schmitt trigger and a few, three I think, passives.

John

Hi

That circuit won't work.

Try this one.

Cheer

Gaetan

Here's a fairly minimal circuit, a lot more parts than under discussion but a lot fewer actives than anything using an IC. Class DA, the circuit itself has good efficiency but the output network ruins things. Excellent linearity though -- less than 0.1% THD!

Tim

It scares me when people talk about excellent audio linearity being 0.1% THD.

Just ordered some Nat Semi samples of some op-amps with so many zeroes in the THD figure that it's simpler to quote it as SINAD instead. It's

-130dB.

Graham

BIPOLAR output devices ?

That circuit must be at least 25 yrs old.

Graham

We can do better on the power stage. The saturation voltage of that circuit is quite high. At least the pull up resistor should be bootstrapped.

Hi

I was, since few months, looking for an easy to build PWM inverter, and without any PIC programing.

Looking again at the 555 PWM amp circuit, I have an ideas, by merging a

Here is the final circuit.

It should work... I think...

Thanx

Cheer

Gaetan

MooseFET ( snipped-for-privacy@rahul.net) writes:

Hum on the +320 supply both adds to and modulates the output.

Sort of reminds one of how awful tubes actually are.

John

"Eeyore" a écrit dans le message de news: snipped-for-privacy@hotmail.com...

Huh... Did you actually look at the drawing? It's a full toobs switching amp and 0.1% is not bad at all considering the stuff involved and that it's an open loop design.

And building such a bizarre amp shows some sense of humor and derision I like.

I thought the brits could easily understand this. Apparently not all of them.

-- Thanks, Fred.

Now that IS impressive.

I'll have to get to understand you better

Had I looked I would have done. My sense of humour is somewhat dry at times so I would have apreciated it. None the less, it goes to show just how far some devices have gone now.

On the subject of tube amps, anyone here heard of the 'circlotron' amplifier ? It was an EV design and I still haven't fully fathomed it. Google will find it.

Graham

Ye Gawds.

My brain hurts now....

Bob M.