Self-bias is not used in class B power amplifier

[Osawa_Odessa]

Hi,
I am reading about power amplifier. Here is a list of advantages and disadvantages of class-B push-pull amplifier over class-A amplifier: https://www.article716.com/enlist-the-advantages-and-disadvantages-of-class-b-push-pull-amplifier-over-class-a-amplifier/
This part I don't quite understand. Hope you can help.
DISADVANTAGES-

(i) Harmonic distortion is high.

(ii) Self-bias is not used.

What do they mean in "Self-bias is not used"? Please explain.

 

[erikl]

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.

 

[Audioguru]

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.

 

[Osawa_Odessa]

Thanks all!
I understand Audioguru but not quite understand erild's point.
If possible, please help me explain it more.

 

[erikl]

... not quite understand erild's point. If possible, please help me explain it more.

My explanation concerns the input biasing. I mentioned 2 possible input biasing schemes: independent from or dependent on the output quiescent (DC) voltage.