The exact opposite of a class A amplifier, the class B amplifier completely shuts off its output devices when not needed (the positive polarity output is off when the signal is negative and the negative polarity output is off when the signal is positive). Class B amplifiers are very efficient compared to class A amplifiers, but they suffer from distortion and a fairly non-linear output. hen the positive polarity output device is turned off during a negative polarity signal, it is not ready to begin operation again very quickly. Where a class A amplifier can produce output instantly since current is always flowing, the class B amplifier must get started up again. hink of a car sitting at a stop light. If it keeps the engine running at full power and full RPMs (using the brake to hold the car back), the car can take off immediately but it is less efficient (like a class A amplifier). If it turns off its engine at the stop light, when the light turns green the car must be re-started and put into gear before it can take off (like a class B amplifier). Invariably, output devices cannot be turned on and off instantly so the class B amplifier results in low linearity and distortion. Class B amplifiers are not used in audio products but are used in devices such as handheld CB radios where power reserves are important.