A type of amplifier design where the output device is always on for both parts of a complete sinusoidal cycle. Class A is the most inefficient of all power amplifier designs, averaging only around 20%. Because of this, class A amplifiers are large, heavy and run very hot, due to the amplifier constantly operating at full power. The positive effect is that class A designs are inherently the most linear, producing the least amount of distortion and are thus often found in high-end audio equipment.