Which statement about Class A, Class B, Class AB, and Class C power amplifiers is most accurate?

• A. Class A achieves high fidelity, but low efficiency.
• B. Class B offers higher efficiency with some crossover distortion.
• C. Class AB is a compromise between efficiency and distortion.
• D. Class C delivers very high efficiency but high distortion (primarily for RF).

Answer: (A)

The main idea here is how the conduction angle of a power amplifier determines its linearity (fidelity) and its efficiency. Class A has the transistor conducting for the entire input cycle, which gives very high linearity and virtually no distortion across the waveform. That excellent fidelity comes at a cost: the device is on all the time, drawing current continuously, which wastes power and generates heat. So, Class A is known for high fidelity but low efficiency.

Class B can be more efficient because each device handles only half of the waveform, but you get crossover distortion around the zero-crossing unless careful biasing or feedback is used. Class AB biases the devices a bit into conduction so you reduce that distortion while still keeping better efficiency than Class A. Class C drives the device for less than half the cycle, achieving very high efficiency but producing a highly distorted waveform, which is suitable mainly for RF with tuned circuits rather than general audio.

So the statement about Class A being high in fidelity and low in efficiency best captures the fundamental trade-off that defines this class, making it the most universally accurate description. The others describe real-world trade-offs too, but they rely on specific operating conditions and often more nuanced design choices.