Self-bias is not used in class B power amplifier

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Osawa_Odessa

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Class-B push-pull amplifiers usually have single (non-differential) input and output, hence their quiescent input and output DC voltages usually are different - contrary to most differential amplifiers. So in most cases, their input bias voltage will be controlled (fixed) by a circuit network which is independent of the output quiescent voltage. I think this is meant by self-bias is not used.

Apart from this commonly used input bias scheme, self-biasing via feedback from the output to the input of course is possible: One just has to care for different DC and AC gain by an appropriate feedback network.
 
A class-B amplifier output is not biased so crossover distortion is produced (there is almost no output until the input to the output transistors reaches 2 x 0.7V in level) and sounds awful. Therefore almost all audio amplifiers have the output transistors in class-AB where they are biased a little and have very low distortion.
 
Thanks all!
I understand Audioguru but not quite understand erild's point.
If possible, please help me explain it more.
 

Osawa_Odessa said:
... not quite understand erild's point. If possible, please help me explain it more.
Click to expand...
My explanation concerns the input biasing. I mentioned 2 possible input biasing schemes: independent from or dependent on the output quiescent (DC) voltage.
 

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