Jfet PushPull amp

Decoupled source resistors. Degrades the efficiency. Watch for imbalance which might bias the transformer.

Graham H

That's very weird. Why do you need to do that?

John

Probably class B or AB.

Have Fun! Rich

And an output filter to deaden the high harmonic blips while it's slewing inbetween?

Ewww...

Tim

I measure noise and distortion in PPM... single digits of same.

Class AB bipolar amps are hardly linear open-loop.

John

So you've got ~80dB NFB? Yea, at what frequency?

Then you didn't design them correctly. Hell, lots of emitter resistors and a few more gain stages and you don't even need a loop.

Tim

It's not a single overall fb loop... there's some local stuff around the output stage.

The driver, usually dueling current sources, slamming into the output transistor bases is a major source of nonlinearity. All sorts of stuff happens near the zero crossing, or elsewhere for reactive loads.

I prefer to drive the loads out of the drains of the fets, not the sources. One of the many benefits is that you can bolt all the fets to a common heat sink with no insulators.

ftp://66.117.156.8/Amp.jpg

John