Amplifier Classes Defined

One of the most effective methods of improving the audio quality in your car is to install an amplifier. In the most basic terms, an amplifier's job is to take a weak input signal, boost it, and send the more powerful signal to your speakers. There are several types of amplifiers on the market you’ll want to know about before deciding which one is best for your car audio project. This article will give you the basics about how an amplifier works and what the different classes of amplifiers mean.

Amplifier Basics

Before getting into what the different classes of amplifiers mean, it will be helpful to describe how an amplifier works. To produce better sounding, louder music, an amplifier must increase the voltage of the audio signal. To do this, an amplifier uses a transformer and a series of transistors. The transformer is made of wound wire that transforms the input voltage to a higher voltage while the transistors modulate the output voltages to the proper channels.

An amplifier needs lots of power to create higher voltages. That power results in two things: high voltage audio signals and heat. Heat is the enemy of every amplifier and ultimately is responsible for the majority of component failures – see some of the common amplifier issues and troubleshooting for more reasons why an amp might fail. An amplifier cannot make more power than it draws, nor will any amplifier output the same amount of power that it draws. This inefficiency of energy is one of the primary reasons for the varying classes of amplifiers.

Classes of Amplifiers

There are dozens of classes of amplifiers that function for different types of roles. In the car audio realm, there are four primary types of amplifiers you’ll encounter. Each type has some advantages over other types while also having some drawbacks. The common classes are A, B, AB, and D.

Class A Amplifiers

Class A amplifiers are rare and expensive, but they offer excellent audio efficiency. This type amplifies both the positive and negative values of the input wave. The transistors run at full power all the time. This means that even when there is no signal, the voltage is converted to heat. A typical Type A amplifier is around 25% efficient, meaning that 75% of the voltage sent to the amp is converted to heat.

Due to the excessive amount of heat these amplifiers generate, they are not commonly used in car audio setups.

Class B Amplifiers

This type is often referred to as a “push-pull” type. A Class B amplifier uses two transistors for each signal. One transistor handles the positive and the other handles the negative signal. This makes for a much more efficient amplifier design than a Type A amplifier. The downside is that there is a significant amount of audio distortion created at the point where the positive transistor and negative transistor take overvoltages from one another. For this reason, Class B amplifiers are seldom used in car audio applications.

Class AB Amplifiers

This has traditionally been the most common amplifier type in use for car audio systems. By combining the positives of Class A and Class B amplifiers, manufacturers can create an amplifier that produces high-fidelity sound and less heat without distortion. This type of amp is used in both car audio and home theater applications because of the accuracy of sound reproduction and efficiency.

Class D Amplifiers

Class D amplifiers are different from other types. Class D amplifiers use circuitry to create pulses of DC power that are corrected through pulse width modulation or PWM. While this process resembles a digital processor, Class D amplifiers are still analog.

Class D amps power transistors at either full power or no power. This process allows for an efficiency of around 90%. That means Class D amps produce very little heat. These amps are also smaller than AB types so they are appropriate for car audio applications.

The downside of these amps is they are not as accurate as Class A types. The PWM process induces distortion which is then filtered out. Class D amps are found in-car audio and PA systems, but only rarely in home theater setups.

Other Types of Amplifiers

The four classes above are the ones you’ll find most often, but there are other kinds on the market. Some are proprietary -like the Boosted Rail system from Rockford Fosgate. Other classes have applications ranging from radio frequency transmission to boosting power within a circuit as in a home computer.

The other types are infrequently in use in-car audio, and you’ll rarely see amplifiers on the market for automotive use that don't fall within the AB or D classifications.

How to Choose the Right Amp

When you set out to build your car audio system, choosing the correct amplifier is essential to getting the results you want. Years ago when Class D amps first hit the market, the distortion levels were unacceptable. They've improved tremendously over time but even to this day, you’ll find people that say Class D amps are terrible for car audio systems.

Class AB amps are the most common type found in-car audio. The biggest downside is that they require a lot of power to overcome the lack of efficiency. When you are planning a system using a very large amplifier you’ll also need to factor in how much power your car's electrical system can provide. You may need to upgrade your alternator or add additional batteries to support the power demands of your system. Choosing the appropriate wire gauge is also critical.

Class D amplifiers require less power than Class AB, but using a low pass filter is essential to prevent distortion. In most cases, installing a Class D amp will be easier than AB. Class D amps are smaller, lighter, and produce less heat than Class AB, making them ideal for installations in small places or areas that don’t get good airflow.

Which Class Sounds Best?

This is a point of contention for many people, and for some good reasons. Much of the debate centers on home theater systems rather than car audio simply as a result of the sound environment. In your car, you’ll have a hard time hearing the difference between comparable-quality Class AB and Class D amplifiers.

Audiophiles, on the other hand, will give you tons of feedback about why Class D amps are terrible. Due to how the amplifier increases the signal, a certain amount of distortion and alteration of the original input occurs. This can make Class D amplifiers struggle to produce certain frequencies well. Class D amplifiers particularly struggle with high-frequency audio signals at high volumes.

Class AB amplifiers are known to produce a warmer, more authentic sound than Class D amps. These are more popular for full-range speakers rather than subs because of the better-sounding frequencies. Many people say that Class D amps simply sound unnatural when reproducing mid- and high-frequencies. Class D amplifiers are very popular for powering subwoofers where the high-frequency signal is not present. You can check out our list of best monoblock subwoofer amplifiers – they're pretty much all Class D.

The average music enthusiast will struggle to hear a difference between Class AB and Class D amps in their car audio system when using a good product. Cheap Class D amplifiers tend to create more distortion and a flat, lifeless sound so if you plan to use this type, it is worth spending a little more money to buy a superior product.

Conclusion

Picking the right amp for your project doesn’t have to be confusing or difficult. The decision to purchase one over the other should focus on how you plan to use the amp. If you are simply upgrading a factory system in hope of getting better sound quality, either amp will work well. If you are installing an amp in a tight space or you don’t want to upgrade the electrical system, a Class D amplifier will make good sense. Most class AB amplifiers are larger, heavier, and get hotter but they typically produce better quality sound than Class D.

We like to recommend Class AB amps for midrange speakers, tweeters, and component drivers where getting accurate sound is important. When you are setting up your system, a Class D amp makes an ideal choice for powering subwoofers. Many of the highest quality Class D amplifiers will perform nearly as well as a Class AB amp and you’ll be hard-pressed to tell the difference between the two under most situations.

Check out our list to find the best amplifiers for cars and trucks, along with our picks for the best amplifiers you can use on boats and offroad vehicles.