In accordance with the different amplifier tube conductive modes, there are different types about the commercial power amplifier
: the first-class amplifier (also known as class A), the second-class amplifier (also known as class B), the first-second-class amplifier (also known as class AB) and the fourth-class amplifier (also known as class D).
The first-class amplifier refers to the commercial power amplifier of which any power output element will not be cut-off current (namely stop output) during entire signal cycle (plus or minus two and a half cycles of the sine wave). When the first-class amplifier is operating, it will produce high heat with low efficiency. However, its inherent advantage is that there is no crossover distortion. The mono-amplifier is the first-class amplifier while the push-pull amplifier can be the first class, or the second class or the first-second class.
The second-class amplifier
refers to the amplifier of which the plus or minus two and a half cycles of sine signal are outputted and amplified respectively and alternately by two "arms" of the push-pull output stage. And the conductive time of each "arm" is half a cycle of the signals. The advantage of the second-class amplifier is that it has high efficiency and its disadvantage is that it will produce crossover distortion.
The first-second-class amplifier
is between the first class and the second class. And the conduction time for each "arm" of push-pull amplification is more than half a period of signal and less than one cycle. The first-second-class amplifier can effectively solve the crossover distortion problem of the second-class amplifier, and it is more efficient than the first-class amplifier, so it has been widely used.
The fourth-class amplifier
is also known as the digital amplifier, which can amplify the audio signal by the extremely high-frequency conversion switch circuit. The amplifier features high efficiency and small volume. There are many fourth-class amplifiers of which power are more than 1,000W but they are just as big as VHS tapes. This type of amplifier is not suitable for use as the broadband amplifier, but there are more applications in active subwoofer.