Class AB vs Class D vs Class A Amplifiers (The Truth)

Norvan Martin
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If you’ve ever glanced at the specification sheet for amplifiers, you know that the amplifier classes are denoted by one or two letters like A, AB, D, H, etc. Class D, A, and Class AB are the most common ones in the consumer home audio industry currently. So, you might need to understand the differences between them. This article provides details that’ll help you discover the differences that matter most to you.

Class A amplifier designs are characterized by their high fidelity, ensuring accurate and pristine sound reproduction, albeit at the cost of efficiency. Class AB amplifier designs are powerful, efficient, and offer good sound quality. On the other hand, class D amplifiers are even more efficient than class AB but have lower fidelity (how accurately a copy reproduces its source) than class AB.

Class AB vs Class D vs Class A Comparison Table

CriteriaClass ABClass DClass A
EfficiencyModerateHighLow
Power EfficiencyModerateHighLow
Heat GenerationModerateLowHigh
Size and WeightModerateCompact and LightweightLarger and Heavier
LinearityGoodGenerally GoodExcellent
Signal FidelityGoodHighExcellent
ApplicationsConsumer and Professional AudioPortable Audio, Car Audio, Home TheaterHigh-End Audio Systems
CostModerateCost-EffectiveHigher

If you are interested in Class D and AB, see the table of differences in the section below.

Class D vs Class AB 

FeatureClass ABClass D
GainMedium - HighHigh
Power CapacityHighHigh
Power EfficiencyVery GoodFair
LinearityGoodDepends

 

What Are Class AB and D Amplifiers Used For?

Class AB amplifiers are designed to achieve an advanced level of efficiency with incredibly lower distortion.

class ab power amplifier

As you might have noted, it combines the best features of Class A and B to come up with a device without most of the drawbacks of these earlier amp versions. Due to the value that this amplifier offers, Class AB has become the most common home theater and stereo amp.

Class AB is 60% more efficient than Class A. However, Class A remains the winner for accuracy. Until recently, AB was the only realistic way of achieving high-fidelity, full-range sound amplification.

Class D amplifiers have emerged as the most famous kings of efficiency. So, they represent the zenith of amp efficiency.

class d amplifier

Due to the efficiency of these amps, they are also ideal for home use. You’ll also find others in cars.

Has Class D Become the Go-to Choice?

Class D amplifiers are highly efficient and make signals rapidly by switching transistors both on and off. This process resembles digital processing. However, these devices are not digital amps. Some of these amps may have digital control circuits, but their circuits are strictly analog.

Many audiophiles say they need to filter out the generated distortion to get value out of these amplifiers.

Do you see why Class D amplifiers are the go-to choice? Class D amplifiers might not serve you well if perfect fidelity is crucial for you. The distortion issue is real.

However, if you’re looking for smaller and lighter amps that run cooler than other options with an equal amount of power, then they are the absolute go-to choice.

Is a Class AB Amp Better than a Class D?

Neither of these amps is necessarily better than the other. It all depends on what you want to get from your amplifier. You might have heard that Class B is slightly more efficient than Class A amps. However, it’s full of distortions. Class A offers a greater degree of accuracy. Class AB is much better than the two combined. It provides an excellent sound response as well as exceptional power efficiency.

On the other hand, the Class D amplifier has the highest efficiency. However, it doesn’t guarantee you the best fidelity. So, you can see that the ultimate decision is yours.

Read on for a summary of the pros and cons of Class AB and Class D that will help you see the significant differences.

Class AB 

Class AB amplifiers’ efficiency ranges between 50% and 70%.

Pros

  • More efficient than Class A.
  • Users can render the crossover distortion moot.
  • Relatively inexpensive.

Cons

  • Efficiency is good but not exceptional.

Class D

The efficiency is typically greater than 90%.

Pros

  • Lightweight
  • Small
  • Best possible efficiency

Cons

  • Pulse width modulators work at low frequencies.
  • They can easily compromise high frequencies.
  • Some designs depend on the speaker load to determine sound quality.

Do Class AB and D Amps Run Hot?

Yes, this is a major concern. Class AB amplifiers get hotter since they are less efficient than class D amplifiers. So, this is another reason class D remains a better option if you don’t consider perfect fidelity an essential feature of a great amp but are looking for amps that run cooler.

For this reason, class AB amplifiers tend to go into protect mode when under too much pressure. 

How Do Class AB and D Amplifiers Get Hot?

When you turn down Class A amps’ volume, they get hotter. This happens because these amps consume the same amount of power irrespective of their power output. For that matter, when you set the gain to a low value, the amp converts the excess power that has not been sent to the speakers into heat energy.

It’s important to note that Class AB amplifiers use the Class A section up to a particular level. So, once they cross the threshold of output power, the heat begins to reduce slightly.

Since Class D amps don’t convert the excess power into heat energy, you won’t experience the same heating pattern. When the amount of power that your audio system demands from your Class D amp increases, the device gets hotter. This should let you see why these single-letter amps often tend to produce a punchier, deeper sound than Class AB amps.

Do Class D Amps Use Less Power than AB?

In a way, we can say that Class D amplifiers use less power. They are highly efficient at turning raw AC power into watts. Apart from that, they don’t waste unused energy.

This means they are more energy-efficient than Class A and Class AB amplifiers. So, these amps don’t use power sparingly but are better than the other alternatives known for wasting large amounts of energy when converting unused energy into heat.

How Hot is Too Hot For an Amplifier?

We’ve seen that Class D and Class AB amplifiers can get hot. One thing you need to note is that neither of them should get too hot. You should consider your amp too hot if its temperature goes above 160F (or 71.111°C). In most cases, your amp may shut off to prevent further damage at this point.

If the surface temperature of your Class AB amplifier exceeds 65° C (149° F), check whether the room temperature exceeds the standard, 40° C (104° F) and if the room is not adequately ventilated. If that’s the case, you can fix this issue by ensuring adequate space around the amp’s cooling vents. That alone is enough to prevent excessive heat buildup. You might also need to create enough space to allow air to circulate freely in the room.

What Is The Difference Between Class AB And Class D Amplifiers?

In reality, Class AB amplifiers are heavier than Class D amplifiers, they typically run warmer, and they aren’t as efficient. On the other hand, Class D amplifiers are super-efficient. They pull less current, and they run much cooler than Class AB amplifiers. It is worth mentioning that they are typically much smaller.

What Class Amp Is Best For Mids And Highs?

Going by reviews and performance, an excellent choice for mids and highs is the P400X4. It’s a CEA-2006 compliant rated amp, giving you certainty about the honest specs and the assurance that the amp will deliver as promised. The signal-to-noise ratio (SNR) at the rated power output is fantastic, at 105 dB. 

Summing Up

You have all the details you need to understand the differences between Class AB and Class D amplifiers. As we’ve seen, Class D guarantees you the best possible efficiency and is lightweight but comes with a few cons. Class AB is relatively efficient and is affordable but might not satisfy some audiophiles. We trust you are ready to use these details to choose the best amplifier and transform your listening and watching experience.

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Norvan Martin is the founder of BoomSpeaker.com. He is a professional Electronics Engineer and is passionate about home theater systems and AV electronics. BoomSpeaker was created as an online hub to share his knowledge and experiences as it relates to home theaters and home audio electronics. My email: [email protected]  Connect on Pinterest and Linkedin