Home Resources Class A vs. Class AB vs. Class B vs. Class C vs. Class D Amplifiers

Class A vs. Class AB vs. Class B vs. Class C vs. Class D Amplifiers

by Stuart Charles Black
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Stuart Charles here, HomeStudioBasics.com helping YOU make sound decisions, so…

In the world of audio amplification, understanding the nuances of amplifier classes is crucial for crafting the perfect sonic experience.

From the purist fidelity of Class A amplifiers to the efficient innovation of Class D counterparts, each amplifier class brings its own set of characteristics and trade-offs to the table.

Furthermore, the distinctions between headphone amplifiers and speaker amplifiers add another layer of complexity, as these devices cater to different impedance loads and power requirements.

In this exploration, we’ll delve into the depths of Class A, Class AB, Class B, Class C, and Class D amplifiers, dissecting their operational principles and applications.

Moreover, we’ll decipher the tailored intricacies of headphone and speaker amplifiers, unveiling the engineering marvels behind delivering pristine audio to our ears.

Join me on this journey as we unravel the symphony of amplifier technology and its harmonious integration into the world of sound reproduction.

What is An Amplifier?

Amplifiers are electronic devices used to increase the amplitude (or strength) of an electrical signal, typically an audio signal in the context of audio equipment like headphones and speakers.

The different amplifier classes refer to the way the amplifiers operate and how they handle the input signal.

Let’s dive into the details of each class and how they relate to both headphone and speaker amplifiers:

Class A Amplifiers

The Mord Chojo is a Class A amplifier.

Class A amplifiers are known for their simple design and high-quality audio output.

They operate by conducting current through their output transistors continuously, even when there’s no input signal.

This means that they’re always “on,” which leads to high power consumption and heat generation, even when idle.

The advantage of Class A amplifiers is that they provide excellent linearity and low distortion, resulting in high-quality sound.

They are commonly used in high-end audio applications where sound quality is paramount.

Class AB Amplifiers

JDS Labs Objective 2

AFAIK, the Objective 2 was a Class AB amplifier.

Class AB amplifiers are a compromise between Class A and Class B amplifiers.

They use two sets of transistors: one for the positive half of the signal and one for the negative half.

The key feature of Class AB amplifiers is that each set of transistors operates slightly beyond its cutoff point, allowing some current to flow even when there’s no signal, but not as much as in Class A.

This reduces power consumption and heat generation compared to Class A while maintaining good audio quality.

Class AB amplifiers are commonly used in a wide range of applications due to their balanced performance.

Class B Amplifiers

The Best Portable Headphone Amps & DACs

The A3 is a perfect start.

Class B amplifiers are designed to address some of the efficiency concerns of Class A amplifiers while maintaining a reasonable level of audio quality.

They operate by dividing the signal waveform into two halves: one half is amplified by one set of transistors during the positive cycle of the signal, and the other half is amplified by a separate set of transistors during the negative cycle of the signal.

This split operation allows each set of transistors to only conduct current for half of the input signal cycle, which significantly reduces power consumption compared to Class A amplifiers.

Key Features and Characteristics


Class B amplifiers are more efficient than Class A amplifiers, especially when there’s no signal input.

The transistors only conduct current when the input signal requires amplification, leading to less wasted power and heat generation.

Crossover Distortion

One significant challenge with Class B amplifiers is crossover distortion.

This occurs near the point where the signal switches between the positive and negative halves.

This transition can introduce a small amount of distortion, which can be audible as distortion or “notch” in the waveform at low volume levels.

Push-Pull Configuration

Class B amplifiers often employ a push-pull configuration, where one set of transistors handles the positive half of the waveform, and another set handles the negative half.

This arrangement helps minimize crossover distortion and improve overall efficiency.

Complementary Symmetry

Class B amplifiers can be further refined into Class AB amplifiers through a complementary symmetry arrangement.

In this setup, the transistors are biased slightly beyond their cutoff points to reduce the crossover distortion.

This effectively combines Class A and Class B characteristics, providing better audio quality without compromising efficiency significantly.


Class B amplifiers are commonly used in audio applications where moderate audio quality and efficiency are desired.

They find applications in audio receivers, car amplifiers, and other situations where energy efficiency is important but a certain level of audio quality must be maintained.

Class B amplifiers strike a balance between efficiency and audio quality, making them suitable for various audio applications.

Their push-pull architecture and ability to reduce power consumption during periods of no signal input set them apart from Class A amplifiers.

While crossover distortion remains a concern, techniques like complementary symmetry help mitigate this issue, making Class B amplifiers a practical choice for scenarios where both efficiency and audio fidelity matter.

Class C Amplifiers

Class C amplifiers are highly efficient but have limited use in audio applications due to their non-linear operation.

They conduct current for less than half of the input signal cycle, resulting in high distortion.

These amplifiers are mostly used in radio frequency (RF) applications, where high efficiency is crucial and fidelity can be sacrificed.

Class D Amplifiers

Class D amplifiers, also known as switching amplifiers, have gained popularity due to their high efficiency and compact size.

They work by rapidly switching the input signal on and off using a pulse-width modulation (PWM) technique.

This switching behavior reduces power dissipation, making them much more energy-efficient compared to other classes.

However, their switching nature can introduce some distortion and noise, which can affect audio quality.

They are commonly used in applications where efficiency and small size are critical, such as in portable devices and subwoofer amplification.

Headphone Amplifiers vs. Speaker Amplifiers

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The primary difference between headphone amplifiers and speaker amplifiers lies in the power requirements and the load they drive.

Headphone Amplifiers

Headphone amplifiers are designed to drive low-impedance loads (headphones) directly.

They typically provide lower power output compared to speaker amplifiers since headphones require much less power to achieve adequate volume levels.

The design considerations for headphone amplifiers involve low output impedance to match various headphone impedance levels and ensuring low distortion to maintain audio quality, especially for high-impedance audiophile headphones.

Speaker Amplifier

Speaker amplifiers need to provide significantly more power to drive speakers, which have lower impedance compared to headphones (typically 4-8 Ohms).

They are designed to deliver enough power to move the speaker’s diaphragm and produce sound at the desired volume levels.

Speaker amplifiers often include additional features such as tone controls, equalization, and protection circuits to optimize performance and protect the speakers from damage.

Why do speakers require more power at a lower impedance?

Speakers require more power because they are designed to produce sound in a larger physical space, typically a room or an outdoor area, as compared to headphones that are placed directly on or in the ears.

This need for higher power is related to several factors:

Sound Pressure Level (SPL) and Acoustic Energy

In order to generate the necessary sound pressure levels (volume) to fill a room or open space, speakers need to move larger volumes of air.

This requires more acoustic energy, which translates to more power.

Higher-impedance speakers can often handle more power, and lower impedance means the amplifier has to deliver more current to drive them effectively.

Dispersion and Coverage

Speakers are designed to disperse sound over a wide area.

This means that the sound needs to be projected in different directions to cover the entire listening space effectively.

Achieving this dispersion requires more energy, which, again, translates to more power.

Bass Reproduction

Generating low-frequency sounds (bass) requires moving a significant amount of air.

Bass frequencies have longer wavelengths, so moving air to produce those wavelengths necessitates more power.

Speakers that can produce deep and powerful bass require even more power to do so effectively.

Dynamic Range

Music and other audio content often have wide dynamic ranges, meaning they have both very quiet and very loud parts.

To accurately reproduce these dynamics, speakers need to handle sudden increases in power demand without distortion.

This requires having ample power reserves available.

Efficiency and Distortion

Efficiently driving speakers with lower impedance often requires more power.

This is because the amplifier needs to deliver sufficient voltage and current to accurately reproduce the audio signal without introducing distortion, which can be especially noticeable at higher volumes.

Closing Thoughts

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The different amplifier classes (Class A, Class AB, Class B, Class C, and Class D) offer varying trade-offs between efficiency, power consumption, and audio quality.

The choice of amplifier class depends on the specific application and the priorities of the user, whether it’s high-fidelity audio, efficiency, or compactness.

Similarly, headphone amplifiers and speaker amplifiers are tailored to the specific requirements of headphones and speakers, respectively, to ensure optimal performance and audio quality.

Well, that’s about it for today my friend! I hope you’ve enjoyed this discussion on Class A vs. Class AB vs. Class B vs. Class C vs. Class D amplifiers and came away with some valuable insight.

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All the best and God bless,





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