Class A/B Amplifiers: The Sweet Spot Between Sound Quality and Efficiency

Why Audiophiles Still Prefer the Balanced Performance Of Class A/B Even Though Class D Is Everywhere

Is Class D amplification the digital to Class AB’s analog? Is it cheaper, better, faster, like Google Docs is to a…typewriter? Perhaps the analogy doesn’t totally fit, but Class D is the “newest” technology on the amplifier horizon, even though it’s been around commercially since the 1970s. By the way, D does not mean digital, although Class D amplifiers have benefited greatly from advances in digital technology, starting with the transistor. Let’s talk amplifier science here, comparing the newer Class D to the tried and true Class AB. Follow along as we will try to explain amplifier science in as non-technical a fashion as possible and explain—spoiler alert—why we think Class AB is still king when it comes to sound quality. 

The Science Behind Class A/B

What exactly is a Class A/B amplifier, and why should anyone care?

As the name implies, you might say that Class A/B design is about finding balance. It’s an elegant solution that combines the sonic purity of Class A with the efficiency of Class B. Unlike Class D amplifiers that rapidly switch transistors fully on and off (essentially operating in a digital-like binary state), Class A/B works in the analog domain, producing a continuously variable output that more faithfully reproduces musical nuances. 

While revered for their exceptional sound quality, Pure Class A amplifiers are rarely practical in home audio. They’re notoriously inefficient—typically, only about 25% of the power they draw actually becomes sound—with the rest converted to heat. That’s why most Class A amps are built like tanks with massive heat sinks. On the other hand, Pure Class B achieves higher efficiency but introduces significant crossover distortion that makes them unsuitable for high-fidelity audio applications.

The defining feature of Class A/B is what engineers call a “push-pull” arrangement. Two transistors share the workload, with one handling the positive part of the audio signal while the other manages the negative portion. This clever division of labor significantly reduces crossover distortion—that unpleasant artifact that occurs when the signal crosses from positive to negative—while keeping power consumption within reasonable limits. The result is an amplifier that delivers excellent sound quality without requiring its own dedicated power plant or operation in an ice-cold room. While Class A/B amplifiers typically achieve around 60-70% efficiency (compared to Class D’s 90%), they compensate with notably lower distortion and superior linearity—characteristics that translate directly to what you hear.

Why Class D Isn’t Always the Answer

To be clear, Class D amplifiers excel in many applications. Their exceptional efficiency (up to 90%) makes them ideal for portable speakers, car audio systems, soundbars, wireless network speakers (Sonos et al), and subwoofers where power management is crucial. They’ve revolutionized (some) home audio components and powered speakers by reducing size, weight, and heat output.

But this efficiency comes with trade-offs that matter to critical listeners. Class D amplifiers generate high-frequency noise that requires filtering, and these filters can interact unpredictably with loudspeaker impedance curves. Sound quality may vary significantly depending on which speakers you connect—stellar with one pair, lackluster with another.

Early Class D designs earned a reputation for compromised sound quality that’s been hard to shake off. While modern implementations have improved dramatically—with some premium models delivering impressive performance—many audio enthusiasts still find they lack the natural warmth and dimensionality of well-designed Class A/B circuits, particularly in critical midrange frequencies. The difference isn’t just measurable in a lab; it’s audible in your living room when you’re trying to lose yourself in your favorite album. And that brings us to the most important factor.

The Listening Experience—What Your Ears Actually Notice

Technical specifications only tell part of the story. What matters is how amplifier technology influences your emotional connection to music.

Class A/B amplifiers typically excel at reproducing micro-dynamics—the subtle volume variations that make instruments sound lifelike. While they may not reach the absolute heights of Class A in audio fidelity, they offer a remarkably high level of sound quality with improved efficiency. This balanced approach preserves the expressive qualities that make music engaging.

The sonic advantages are most evident in how Class A/B handles the critical midrange, where vocals and most instruments reside. Voices have body and dimension, and acoustic instruments sound more tangible. The soundstage—that illusion of three-dimensional space—tends to be more precisely rendered, with instruments occupying distinct locations rather than blending together.

Bass response also often benefits from Class A/B’s linear operation. Rather than just sounding loud, low frequencies feel more controlled and articulate. You hear the texture of a bass guitar or the subtle resonance of a kick drum, not just the boom. These aren’t just audiophile obsessions. Even casual listeners can hear the difference in critical listening situations. They might not describe it in technical terms, but they’ll recognize when something sounds more like live music and less like a recording.

It’s About the Music, Not the Specs

We don’t have an axe to grind, nor are we audiophile Luddites. Different amplifier technologies have their rightful place in the audio ecosystem. As lovers of music, we’re just presenting our view on what sounds the best, and we want to educate you to make the right choice for your listening experience.

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