We all know what car amplifiers do in regard to boosting the audio signal of a head unit, but not everyone understands or knows, the difference between the different amplifier topologies, or classes. In this post, I will explain the two most popular topologies used for car audio, class A/B, and class D.

In addition, I will discuss other topologies that are not used for car audio (class a and class B) just to give you some background on the class A/B topology. Before we begin, let’s look at class A and class B amplifiers. These are the two topologies on which the class A/B amplifiers are based. 

Class A

Class A amplifiers utilize all of the audio signal input, all of the time. This means that the amplifier is duplicating the signal from the head unit, or audio source, with little to no clipping or distortion. The drawback of class A amplifiers is the creation of extreme heat. This is because these amplifiers are “on” all the time, even when no audio signal is being sent to them. The trade-off for the heat is sound quality. But, on the other hand, class A amplifiers are typically not used in car audio applications because this topology can generate 500 watts of heat to get just about 100 watts of power output. Because the trade-off isn’t great for car audio, class A amplifiers are typically used for low-power audio components like headphones.

Class B 

Class B amplifiers utilize two output devices, which handle conducting signals alternately. This means that about 50% of the audio signal is used, so only half of the signal wave is amplified. Dealing with the audio signal this way creates a lot more distortion than the class A amplifiers, but allows to class B amplifier to be way more efficient. 

Now that we have some background on class A and class B topologies, let’s take a look at the two that are pertinent to car audio, class A/B, and class D.

Class A/B

Class A/B amplifiers, from the name, take the best of both class A and class B and combine them to create an amplifier that can produce a fairly clean audio output and be more efficient at doing it. The class A/B amplifiers can accomplish this task because they run very close in nature to class B. This means that where only about 50% of the signal is being amplified and the other half is “off”, the class A/B amplifier amplifies more than 50% of the single, thus reducing the time in between when both signals are “off.”

A class A/B amplifier is a good mix of class A and class B because, for the average audiophile, the volume level is relatively low giving you the sound quality you desire from a class A amplifier, but when the volume is turned up, the output signal still remains less distorted than the typical class B amplifier.

Class D (Digital)

Class D amplifiers are the most efficient amplifiers used for car audio today. They can achieve an efficiency rating over 90% or higher. This is extremely higher than the 75% efficiency, typical of class A/B amplifiers. Because these amplifiers are so efficient, they require less power from your vehicle, smaller heat dissipation devices (heatsinks), and can be manufactured with small components, hence the age of the mini and micro amplifiers like the Sundown Audio SAM series amplifiers.

Class D amplifiers work by switching their output devices “on” and “off” unlike the class A amplifiers, which remain “on” even without an audio signal. By switching “on” and “off,” these amplifiers create “noise” within the output signal that needs to be reduced. This task is performed by a technique called Pulse Width Modulation (PWM). Trying to make the output signal of a class D amplifier “clean” is a difficult process. This is why most class D amplifiers are for powering subwoofers. The reason is that a subwoofer doesn’t need a quality output signal (because of their frequency range) like a component set of speakers. Most class D amplifiers have extremely low output impedance, which also makes them great for subwoofer applications.

Some class D amplifiers are giving class A/B amplifiers a run for their money. These high-quality class D topologies are giving the same output as traditional class D amps, but are also providing much better sound quality overall.

“D” Doesn’t Always Mean Digital

Being class D doesn’t mean the amplifier is a “digital” amplifier. The letter “D” is just a moniker given to this class of amp because there is also a class C amplifier, so “D” was just next in the naming of the classes. There are class D amplifiers that are digital. This type of amplifier uses and is controlled by digital circuitry. What the digital circuit does is convert the audio signal into a binary signal and then is processed further to remove any errors from that signal before it is outputted to the speaker or subwoofer. 


It’s not rocket science, but it can get confusing sometimes, especially when trying to decide which topology is right for your car audio setup. Personally, I run a class A/B for my midrange and high frequencies and utilize a class D for the subwoofer. But, on the other hand, it’s all personal preference and budget that will ultimately determine this choice for you. I hope this post has shed a little more light on the different amplifier classes and has given you a better understanding of how they perform and how they differ. 

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** Please note that this article provides general information on amplifier topologies (classes) in a car audio system. Keep in mind that not all vehicles are the same and may require different installation methods and techniques to ensure a safe and effective install. By no means, am I a professional mechanic or car audio installer, and D4S and I, are not liable for any damages caused to your person or vehicle by following these instructions. Please consult a professional if you have any questions or concerns regarding your own vehicle and how to perform modifications such as the one explained in the previous statements.

How to identify feedback topology of an amplifier.

About The Author Brandon L

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