Quiescent Current Control, NFB, and Push-Pull Pairs

[featherpillow]

A push-pull output pair can shift in and out of its class under load. Can't this sort of problem be controlled using some type of compensation? For example, in a Class B output pair, we can design local compensation into the output stage to help improve linearity and minimize crossover.

Can't the same be done for Class A or AB? Some type of current controlling device that could, say, sample the current drawn through the output pair's emitter resistance, regulate the quiescent current, and turn on and off when the current draw is looking low?

 

[clintrubber]

I think you mean something that's called 'adaptive biasing', right ?

Just one of the links popping up:

http://www.marklevinson.com/products/overview.asp?cat=pa&prod=no434&details=yes

Adaptive biasing is used to manage the power source of the output stage for best performance without excessive heat generation or waste of energy. First developed for the No.33 Reference Monaural Amplifiers, adaptive bias technology has proven its worth in thousands of installations using Mark Levinson amplifiers. Adaptive bias delivers the benefits of low switching-distortion possible from class A designs, with the efficiency of typical A/B amplifiers.

The result is a sonic character that suggests unlimited reserves of power while also retaining the finesse associated with the best sounding low-power amplifier designs.

I thought I heard Marantz uses this as well somewhere, as will be countless other designs.

 

[featherpillow]

Mark Levinson? Don't those amps cost like a billion dollars?

 

[Samuel Groner]

You're looking for the D. Self class A feedback regulator:
Self_Bias.gif

Samuel

 

[featherpillow]

Ha! I have his book--I see now that he actually discusses this in chapter 9. I'm only on chapter 3 right now.

 

[bcarso]

Many are the ways.