What Are The Different Amplifier Classes for Car Audio?

What are the Different Types of Audio Amplifier Classes

An audio amplifier has a particular purpose in the world of sound production. The audio amplifier’s design serves the system by reproducing input audio signals at specific output elements. The desired power levels are achieved, and the correct volume is reached.

Ideally, the right kind of audio amplifier will improve the sound’s overall quality. At the very least, a lousy amplifier will distort the sound and worsen the overall quality. So having a good audio amplifier will make a difference in the long run.

The audio amplifier is divided into different lettered categories to determine what they do, the power levels they can reach, and how they perform. The grading system describes how each audio amplifier functions at a core, fundamental level.

Each audio amplifier has the same primary job, although they each have different strengths and weaknesses in performing the job. The amplifier is supposed to amplify the waveform that the preamplifier sends it, and it must do so with interruption or distortion. The different audio amplifier classes grade how each amplifier performs this job.

Audio Amplifier Classes

There are nine basic classes overall, though three are less common. Those will be discussed at the end of this article. The amplifier classes that will be addressed include:

  • Class A
  • Class B
  • Class A/B
  • Class C
  • Class G
  • Class H
  • Class D
  • Class I
  • Class S
  • Class T

The class system for audio amplifiers marks the clear distinction between each type of amplifier and how it operates. Some classes are markedly better or more effective than others.

The class system can also signify the circuit configuration for each amplifier and how they operate. Each different class has a specific output signal, ranging from a linear operation to a non-linear process. Anything in between is a form of compromise between these two modes.

While each amplifier class is slightly different in the way it functions and its output signal, they are all related by the linear scale of operation.

An entirely linear operating system amplifies high-fidelity signals, otherwise known as the lossless level because it is considered the best sound.

A non-linear operating system works when a proper, entirely accurate signal reproduction is unnecessary. This can lead to more output signal distortions.

Each audio amplifier class designation is vital to help you understand where the amplifier ranks in terms of sound reproduction quality.

Related: Our guide to the best monoblock car amps

Class A

The class A amplifier conducts over the complete input cycle range. Class A is relatively simple compared to the other classes on this list. A few of the essential characteristics of the class A amplifier include:

  • It can operate as a single-ended amplifier
  • Can serve as push/pull amplifier
  • Use one output switching transistor
  • Conducts over full 360 degrees of the input cycle
  • Fully linear
  • Low signal distortion levels
  • High fidelity amplifier

Class A is considered one of the most straightforward amplifier designs, but it is considered the best amplifier on the market. Because it is straightforward to use, it’s prevalent. And because it delivers such a high-quality sound, it’s well worth the simplicity.

One downside to the class A amplifier is its tendency to continuously lose power, which causes an influx of heat and a loss of efficiency. For high-power jobs, they are not the most practical selection.

Class B

In response to the heating and efficiency issues of the class A amplifier, the class B amplifier came into existence. The result is a solid amplifier with lots of benefits. However, the class B amplifier cannot operate over the full 360 degrees of the input cycle.

The class B amplifier features a few important characteristics:

  • Push/pull arrangement allows for 180 degrees of operation
  • More efficient for professional settings
  • Known for crossover distortion issues

While made in response to the class A amplifier, the class B amplifier was not met with the same welcoming acceptance by professionals and amateur audio fanatics.

Class A/B

The class A/B amplifier combines the primary or useful components of class A and the class B amplifier. At its most basic level, it is a variation of class B. Because of technological improvements, however, class A/B solved the crossover distortion issues associated with class B.

The goal of the A/B amplifier was to create an amp that had neither A nor B’s flaws. The amp is more robust and more efficient, improving the efficiency problems of class A by almost 50%. It’s also more substantial than class B, increasing to 200 degrees of operation across the input cycle.

As far as improvements go, the class A/B amplifier delivers on its promise to be a better version of its predecessors. It has a small bias voltage, which improves the problems in distortion without producing inefficiency or overheating.

Class C

The next iteration of the amplifier class is class C. While it is the most efficient of all previous amplifier classes, it lacks linearity. The non-linear element means that the class C amplifier only operates around 90 degrees of the input cycle.

Class C introduces a new level of distortion to the output signal that is much worse than class A despite its high efficiency.

In certain circumstances, the distortion level comes in handy as a radio frequency amplifier but is otherwise impractical for audio amplifiers.

Class G

The class G amplifier is not technically recognized as an audio amplifier class. They utilize a rail switching mechanism that is supposed to make the amplifier more efficient and less prone to power consumption. While they are more efficient in most cases, they lack the overall design to make them effective in the field.

Class H

The class H amplifier is not an officially recognized class similar to class G. The basic idea of the class H amp was to utilize a high-voltage power supply to properly power a high-output system. Where class G failed, class H was able to continuously vary the power supply voltage to account for varying thresholds.

Class G and Class H were initially created to improve the efficiency problems of class A/B. While they succeeded in solving the efficiency problem, they both require remarkable power. This adds to the cost of operation and makes them less practical for use as audio amplifiers.

Class D

The class D amplifier changed the way that other amplifiers utilized output devices. Where other amps had one output device that was constantly active, the class D amplifier switches between output devices in an on and off state, this produces a tight control of the output devices, creating more efficiency.

The class D amplifier is known for:

  • Efficiency greater than 90%
  • Non-linear switching capabilities
  • No voltage or waveform overlap
  • Current drawn through the transistor

Class D audio amplifiers are highly efficient and have only recently become available on the public market. There was a time when the class D amplifier served as the subwoofer in automobiles.

Is One Class Best?

As this discussion of audio amplifier classes shows, each amplifier class has different features that make it useful.

The class A amplifier has the highest sound fidelity, while the class B design is more efficient. Classes G and H are highly productive in almost every capacity, and class D reaches efficiency levels greater than 90%.

For each positive feature, every amplifier class has a drawback as well. Despite having great sound fidelity, Class A is by far the least efficient of all the classes. And while the class C amplifier is incredibly efficient, it introduces an entirely new level of distortion.

Picking one amplifier class as best depends on your needs for the amplifier. The class A amplifier is more widely distributed than others. Even though it lacks efficiency, it makes up for the sound fidelity and price point.

If you had to pick one, class A would be the one. Generally, the class A audio amplifier is considered the best because of its audio quality, low signal distortion levels, and excellent linearity.

Some Other Classes

Another subsection of audio amplifier classes deserves a brief mention, as they have each co-opted different elements of the main classes.

Class I

The class I amplifier is designed similarly to class B. With no input signal applied, the class I amplifier can cancel out high-frequency signals. The sound produced is considered powerful and highly accurate.

Class S

Operating similarly to the class D amplifier, class S is theoretically capable of reaching 100% efficiency. The unit is most commonly used for low-frequency signals or radio frequencies and digital input.

Class T

The class T audio amplifier is another variation of class D. Designed by the company Tripath, class T has a crisp, clean sound and holds a lot more power. It is another digital switching design, becoming more popular as technology advances.


The amplifier class system has become a significant part of the audiophile culture. Audio amplifiers come in all different types of classes and designs. These classes help determine how the amp works, what its output capacities are, what the amp wiring process looks like, and how efficient or inefficient each one is at its most basic operating level.

Brett Gordon

The engine behind editing at DigMyRide and the brains behind its build. During the day, Brett is a thirty-something dude from SoCal climbing the corporate ladder, but by night, he spends his time contributing to the online world of automotive tech & trends.