It's well known among designers of power amplifiers that the class-A and -A/B amplifiers (referred to as linear amplifiers) used in the majority of car, home, PC, and pro audio systems are notoriously inefficient. They can consume vast amounts of power and yet waste most of it---as much as 80% or more---as heat. They require large power supplies and massive heatsinks, which drive up system weight, size, and cost. On the other hand, class-D amplifiers, using Pulse Width Modulation switching technologies, have good power efficiency but sometimes questionable audio fidelity. (The Spectron designs are possibly the exceptions here.) Class-D amps are used mostly in battery-powered applications in which sound quality might be considered secondary to battery life.
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