What's the difference between B, AB and C amplifiers and what's the basis of this classification? I ran into a sound engineer who tried to explain the difference but it was all Greek. Again, which one is the most suitable for use as an audio amplifier?
Wayne Parham Messages: 18786 Registered: January 2001
Illuminati (33rd Degree)
Class A and class AB are suitable for high-fidelity audio, classes B and C are not.
Class A is often called single-ended because it uses one active element to amplify both positive and negative cycles of the waveform.
Class AB is often called push-pull because it uses two active elements, one for each side of the waveform, positive or negative. But there is sufficient overlap so that each active element is operating within its most linear region, limiting distortion during the "hand off," commonly known as crossover distortion.
Class B is also push-pull, but there is no overlap. Each active device operates only during its half-cycle. Efficiency is higher than class AB but distortion is higher too.
Class C is a special-purpose configuration, used mostly in RF circuits. It amplifies only the top portion of the wave. Very high efficiency but also very high distortion. This distortion isn't a problem in some cases, so it is useful because of its efficiency.
gofar99 Messages: 1949 Registered: May 2010 Location: Southern Arizona
Illuminati (5th Degree)
Hi, Simple and dirty description follows.
You can also can have class A push pull amps. All my power amp designs fall into this class.
Class A amps have power flowing though the output devices (transistors, tubes) all the time.
Class B amps have the output devices running at 1/2 of each cycle of power. One device will be on while the other is off. '
Class AB has class A operation at low power and goes to B at higher levels
Class C is less than 50% on each output device (can be a single device as in transmitter output stages).
Other classes are not consistently defined. Class D , T, and H are made up with high frequency switching devices. The pulses are summed to obtain the audio output.
Matters sound can be quite complex and confusing at times but I think the whole point is in grasping the basics. Many people have the interest to know these things but don't go as far as they should.
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