An audio amplifier is an electronic device that amplifies the electrical signals that go through it to power up sound outputs like loudspeakers and radio. With the help of an external power supply, an audio amplifier boosts up the low power audio signal by controlling the output to match the input signals shape. The gain of the amplifier relates the magnitude of an input signal and the output.


There are different classes of an audio amplifier such as A, B, G/H, D.

The categorization is done by several factors such as bandwidth, gain, output power, supply voltage. By class, we mean the ability of the respective amplifier to perform the same task of amplifying the input audio signals and giving a distortion-free output.


One of the simple electronic device amongst the audio amplifiers, class A operates with the output device of the amplifier, conducting through 360 full cycles of a signal waveform. It is considered as the benchmark audio amplifier among the sound enthusiasts.

The class A  amplifier are further divided into push/pull and single-ended amplifiers. Both the amplifiers perform the basic function of class a except that while one shoulder most of the load in a positive cycle, the other one does the same in a negative cycle, which gives very accurate sound production.

They consume a lot of power and generate excessive heat which makes them least efficient.

Class B:

Unlike the class, A amplifier which conducts a full 360-degree cycle in one phase, in Class B amplifier, half of the cycle conducts in one phase. The push-pull amplifier is utilized in such a way that half of the output device conducts at one time, i.e., it covers +180 degree cycle while the other half conducts at another time, i.e., 180-degree cycle. Hence they are comparatively more efficient than class A.

But since the signal is split into two waveforms, there comes a time when they crossover leading to severe distortion and adversely affecting the sound quality.


Primarily used for home theatre systems and car stereos, Class AB amplifier utilizes the efficiency Of Class B amplifier and sound quality of class A amplifier. The push/pull amplifier of class b is utilized in such a calculative way that when the half cycle is conducting, class A/B amplifier increases it to up to 200 degrees, thereby reducing the potential of any crossover distortion to the point of it being ineffective on the overall performance of the amplifier.

Like class an amplifier, it does get heated up, but that’s negligible.


A minor variation in the driving voltage of the Class A/B  amplifier forms the basis of operation of Cl\assG/ Class H Amplifier. It makes use of lower rail voltage, thereby significantly reducing the power consumption. As the need for high power arises, it switches the output signal to a second higher voltage and efficiently handles the load.


The most efficient amplifiers in the class with 80% efficiency range, they are also referred to as digital audio amplifier. The output stage is directly proportional to the instantaneous value of the input signal, but when switching frequencies, there is a harmonic distortion at the output that needs to be filtered. Used in desktop systems and home theatre receivers, they  produce higher quality sounds and are continually improving with the implementation of better filter and getter methods.


An audio amplifier has found its use in several domains such as

Instrument amplifier for guitars or the keyboard amplifiers;

Home theatre systems: loudspeakers;

Concerts and theatre sound system;

Public address sound system