What Is the Difference Between Class AB and Class D Amplifiers?

You may think that the similar names mean both classes operate in the same way.

It’s actually more complicated than that. So, what is the difference between Class AB and Class D amplifiers?

Class AB and Class D amps don’t operate like each other and don’t apply to the same appliances. They also don’t have the same output.

The only commonality between them is the name. We’ll tell you everything you need to know about the differences, but first, let’s see what an amplifier class is.

What Is An Amplifier Class?

Amplifiers work by converting the incoming DC voltage into AC power through the transformer. It then mixes the power and the stereo’s signal to generate a high-current output.

The amplifier class is the system that’s responsible for mixing the voltage and the signal. Classes vary according to the amplifier type you’re using. Some are more efficient than others, and some provide more fidelity than others.

There are five known amplifier classes: Class A, Class B, Class AB, Class C, and Class D.

But, we’re here to discuss the differences between Class AB and Class D amps.

Class AB vs. Class D – Everything You Need to Know

We’ll tell you everything about the two classes and what distinguishes them from each other.

Class AB

It’s a no-brainer that Class AB is a combination of Class A and Class B amps. The upgrade aimed to solve the problems in both classes. One upgrade that resulted is an increase in efficiency, and that’s exactly what happened. Class AB amps are now the most used amplifier class in home theaters and stereos.

Instead of the distortion issues of Class B amplifiers, Class AB amps allow both devices to conduct simultaneously. That way, the crossover with the waveform doesn’t cause any distortion. Moreover, it offers 60% more efficiency than Class A.

Class D

A Class D amp is actually an analog device. Then why the letter ‘D’? The reason is simpler than you think. It was the next letter in the alphabet after Class C. We’re dropping the knowledge bombs on your head now!

The Operation Method

Each class works differently than the other. Let’s see how operating Class AB differs from operating Class D.

Class AB

Class AB operates as a combination of Class A and Class B. The exception is that it upgrades Class B’s conducting method, instead of the 180 degrees output of the push/pull arrangement, it bumps up to 200 degrees.

This helps reduce the chance for a cycle gap, which consequently means the distortion gets reduced by a good amount.

It does this by keeping the push-pull transistors’ pair on most of the time. They don’t turn off suddenly like the way it is with the previous classes.

Class D

Class D operates in a way of its own, unlike most other classes that operate in similar ways. It produces DC in the shape of high-frequency pulses; over 100kHz.

The pulses then adjust to the signal in a process called ‘Pulse Width Modulation’. Meaning, if the signal is loud, the pulse gets wider, and so on.

This causes the pulses to pass through the transistors to produce the output.

The thing about Class D amps is that the transistors either work on their full power, or turn off with no power at all. There is no in-between; this is mainly because of the DC pulses they’re getting. This method provides 90% efficiency.

The Applications

Class AB

Thanks to their high linearity and quality output, audio enthusiasts prefer Class AB amplifiers over other classes. Their most common use is in home theatres.

Class AB amplifiers are also used in audio power amplifiers, hi-fi systems, and AV hi-fi receivers. The simple design and the minimal distortion account for sensitive uses.

Class D

Class D amplifiers are now the go-to choice for a lot of applications. For example, it’s the most common amplifier for public address systems and speakers. Additionally, it’s now used in almost all car audio systems.

Class D amps have gained a wide popularity thanks to their small size and lightweight. That way, you can carry them around and fit them anywhere. They also don’t produce as much heat as other amplifiers do.

Advantages & Disadvantages

Each amplifier class has its advantages and disadvantages. These advantages/disadvantages should help you decide which amp is for you.

Class AB Advantages

Class AB has a relatively simple design. It’s easy to handle even for the inexperienced. Additionally, it has a linear behavior, which means that the circuit output is an exact multiplication of the input.

Furthermore, the amplifier’s output has a distortion level that’s less than 0.1%. This results in pure, high-quality sound.

Class AB Disadvantages

The most prominent disadvantage of AB amplifies is the generated heat. The power dissipation demands a large amount of heatsink.

Moreover, the efficiency of Class AB amplifiers is lower than others. The average efficiency doesn’t exceed 50%.

Class D Advantages

The 90% efficiency is the most eminent feature in Class D amplifiers. What’s more, the lower power dissipation accounts for the minimal heat generated.

Class D amplifiers are also small in size and portable.

Class D Disadvantages

Unlike the simple design of Class AB amplifiers, Class D amps are much more complex.

Besides, the switching of the output transistors causes sound distortion to occur. As opposed to the low distortion of AB amplifiers.

Final Thoughts

If you’re looking for a portable amplifier that’s small in size and can fit anywhere, Class D is your go-to amplifier. The 90% output efficiency is also a bonus.

On the other hand, if you’re looking for an amplifier that’s easy to handle, Class AB amplifiers will be a good option for you. Additionally, its low distortion accounts for the pure sound. Keep in mind that the preamp needs to be a good fit too.