2. amps-preamps
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Difference between Class a and a/b

Hi,

I have been reading alot about class a and class a/b biased amps, but I am not really clear on what the difference is. I understand that it has to do with circuit providing power through the entire cycle. But I was hoping that someone may be able to explain it in simpler terms.

Any help is greatly appreciated.

Thanks

Craig
species253

Showing 1 response by zoya

zoya
120 posts
 
Craig,
I will try to explain it more technically, but maybe it will make more cents. Your amplifier is working to deliver some signal to the output. If you draw imaginary line through the center of that signal you will divide it into a positive half and a negative half. In Class A amplifier a single output device controls the flow of the entire signal. To do so it has to be biased in such a way that the lowest point of the negative signal still has to be above 0 level, at which point output device (transistor, tube, FET, etc...) shuts off and clips (distorts) the signal.
In class AB amplifier the output signal is controlled by a pair of output devices, where each one of the pair controls only the positive or the negative half (push-pull) of the signal. So each one is biased to be shut-off at zero crossing and stay off while the complimentary one is working on the opposite half of the signal (hence the crossover distortion).
This is basically how they work. I hope that my explanation was clear enough to follow.
Well... I tried...:)
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