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If you’ve been shopping for home theater components, you may have seen the Class D amplifiers mentioned. But what are they and what are they for? Let’s dive deeper into these highly efficient wonders.

An introduction to amplification

At the most basic level, a traditional amplifier is a signal booster. Give it an input signal and use electricity and various gain stages to increase the amplitude until you end up with a much louder signal than what went in. The end result: a stronger signal than the input signal.

There are multiple types of amplifiers like class A, class B, and class AB. Class A and B have their own benefits and drawbacks, while class AB amplifiers combine elements of each to maximize the benefits and minimize the drawbacks of each. For years, the vast majority of consumer electronics, such as A/V receivers and home theater systems, have used class AB amplifiers.

Why do we spend so much time talking about other amplifiers when this article is about class D amplifiers? Because they work very differently.

How Class D Amplifiers Work

A class D amplifier is also known as a switching amplifier. Instead of boosting the input signal through linear gain stages, a class D amplifier uses a concept known as pulse width modulation.

This is a tricky subject, but this converts the input signal to pulses. The output stage then switches back and forth at a high frequency, corresponding to the pulses the signal was converted into. This amplified signal is then processed and low-pass filtered to return it to its original waveform and remove high-frequency noise.

This conversion to and from another type of signal is somewhat similar to how the reverse conversion works and digital to analog but this is much less complex. That said, the process (probably combined with the “D” in class d) leads to people sometimes mistakenly referring to class D amps as “digital” amps.

What Makes Class D Amplifiers Special?

Because pulse width modulation allows amplification to occur at much higher frequencies than normal, class D amplifiers require much smaller power transformers than class AB amplifiers. That means you can pack a lot more amplification into a smaller space.

These amps are very efficient and produce more volume with less power. Class D amplifiers often have maximum possible efficiency values ​​of 90 percent or more, while Class AB amplifiers rarely exceed 60 percent efficiency.

Of course, class D amps aren’t perfect. Due to the low-pass filter, which is meant to filter out unpleasant noise, the high-end can suffer, so they’re not ideal for audiophile use. Some class D amps can also exhibit distortion, and some people, particularly audiophiles, just aren’t fans of the sound of these amps in general.

Even with the downsides, that combination of high efficiency and small size makes Class D amplifiers perfect for certain applications.

Common Uses for Class D Amplifiers

As you can imagine, Class D amplifiers are a great choice for any audio project where size and power efficiency (think battery life) are important. Because of this, you will often see Class D amplifiers employed within bluetooth speakers .

The headphones Bluetooth they are also a good candidate for class D amplifiers, although because the volume requirements are quite low, other types of amplifiers will also work for this particular case. You’ll also find Class D amplifiers in many other products, including headphones laptops and even stereo amplifiers.

Subwoofer connections on the A/V receiver
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An important area where class D amplifiers are frequently used is subwoofers. Looking at the pros and cons of class D amps, it almost seems like they were created for subwoofers. This is because audio problems essentially disappear when the amp is only used for low frequencies, and the small size and efficiency allow you to pack massive power into a subwoofer.

Take a look at our list of best subwoofers you can buy and, if it is powered, the subwoofer is most likely using a class D amplifier.

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