Type of amplifier (amplifier class) in which both the negative and positive polarity output devices conduct at all times so that a current is always flowing through them. The result is a very inefficient amplifier at around 20 percent efficiency (it only outputs 20% of the power it gets from its power supply). Class A amplifiers are thus very large, heavy and hot-running amplifiers. However, since their output devices are always on, they can provide instant power in a highly linear fashion. lass A amplifiers feature the lowest distortion and greatest linearity of the various amplifier classes. The output device of the amplifier is the electronic component that puts out power in watts to drive the speakers. Its polarity refers to the signal being negative or positive. A positive polarity output device does not need to be on when a negative polarity signal is present (this is how Class B amplifiers operate), however, if it is turned off it takes time to start it again when it is called upon to output power. So, class A amplifiers that always have full current to the output devices are ready to deliver power with no lag time and little distortion.