12 Volt Encyclopedia · Volume VII · Article 3
Amplifier Classes Explained in Plain English: Class A, B, A/B, G, H and D
Amplifier class describes how output devices conduct and how internal voltage is managed. It does not grade sound quality like a school report card. A carefully engineered Class D can outperform a poor Class A/B, and vice versa.
Class A
The output device remains conducting through the entire waveform. This avoids switching between devices but wastes tremendous energy as heat, even at idle. Pure Class A is uncommon for high-power mobile use.
Class B
One device handles the positive half and another the negative half. Efficiency improves, but the handoff near zero can create crossover distortion.
Class A/B
Both devices conduct slightly around the handoff, reducing crossover distortion while retaining reasonable efficiency. It became a standard for full-range car audio, though substantial output still becomes heat.
Class G and H
These designs reduce wasted voltage. Class G switches among supply rails; Class H varies or tracks rail voltage more continuously. The output section does not need to burn off as much unused voltage during smaller musical moments.
Class D
Output devices switch rapidly between states rather than operating continuously in the middle. Pulse timing represents the music, and an output filter plus the speaker load recover the audio waveform. “D” does not mean digital.
Efficiency and heat
A 1,000-watt amplifier at 80% efficiency draws 1,250 watts and must dispose of about 250 watts as heat. At 60%, it draws about 1,667 watts and sheds roughly 667 watts. Efficiency changes chassis and electrical demands.
Choosing a class
Use actual distortion, noise, efficiency, load stability, size and power data. Class describes architecture; execution decides performance.
Installation and testing checklist
| Checkpoint | What to verify |
|---|---|
| Compatibility | Source output type, receiving input type and allowable voltage range match. |
| Routing | Signal wiring is protected, secured and separated from likely interference sources. |
| Termination | Connectors fit firmly without excessive force; no cable weight hangs from a jack. |
| Signal | Every channel is identified, clean and unclipped at the intended source level. |
| Final test | Polarity, channel assignment, noise floor and operation are verified with the vehicle running. |
Frequently asked questions
Is Class D digital?
No. It is a switching power-output method and can accept analog signals.
Does Class A always sound best?
No; topology alone does not guarantee performance.
Why does A/B run hotter?
Its devices spend more time dissipating voltage and current simultaneously.
Is Class H a form of D?
No. It generally describes rail management and can accompany different output approaches.
Which is best for subwoofers?
Class D is common because high efficiency suits large bass power.