Main classes of amplifiers:Class A amplifiers gives the least distortion, but are terribly inefficient. They are rarely used in commercial amplifiers because they produce too much heat and give too little output power for the effort.Class A/B is what most commercial amplifiers are. They are much more efficient, but do produce more distortion.Class B amplifiers have two transistors, one per supply rail. In properly-biased class B, only one conducts at a given time, but there is always one conducting.Class D amplifiers are a rather new phenomenon in the hifi world. They are extremely efficient (80%) and can give a very good result.