Amplifier Classes (A, AB, D, G, etc.) are categories that describe the circuit topology of a power amplifier, that is, how its transistors work.

1 Each class represents a different balance between sound fidelity and energy efficiency.

Class A

It is the class with the highest sound fidelity. Its transistors are always on (conducting 100% of the time), which eliminates crossover distortion.

However, it is extremely inefficient (around 25%), as it wastes most of the energy as heat, even when there is no audio signal. It is the choice for audiophiles seeking maximum sound purity. Class AB is the perfect middle ground and the most common class in hi-fi and studio amplifiers. Each transistor conducts slightly more than half the time, operating in Class A for low-volume signals and switching to Class B (where each transistor amplifies half the wave) for high-volume signals. This offers excellent sound quality, very close to Class A, but with much higher efficiency (around 50-65%). Class D It is the most efficient class of all (above 90%). It works like a switch, turning the transistors on and off thousands of times per second (using a technique called PWM) to create the sound wave. Because it generates very little heat, it allows the creation of very powerful, small and lightweight amplifiers. Although once considered of lower quality, modern Class D amplifiers have achieved sound fidelity comparable to Class AB and dominate the market for active speakers, car audio, and subwoofers. Class G and H are more efficient variations of Class AB. Instead of having a single supply voltage, they have multiple voltage "steps." The amplifier uses a lower voltage for low-volume sounds and only activates the higher voltages when the music demands power peaks. This reduces energy waste, making them more efficient than traditional Class AB.