We are guessing you are realizing there is a lot more to amplifiers than you previously thought. They go well beyond simply choosing the one that has the most wattage. So far, you have had to consider what type of amplifier you want, where you want it, how many speakers to connect to it and more. Well, it gets even more complex now with the class of amplifiers. These classes are Class A, Class AB, Class D and Class T.

How the classes come into play, is to do with the efficiency of the amplifier. The efficiency is measured by how much of the input power is applied to the output of the amplifier. Therefore, how much of what goes in, is actually used with what goes out.

Now, you will probably assume that Class A is the best kind you can get, but the truth is that they are the worst. This is because Class A amplifiers operate with a range of about 10 to 20 percent efficiency, with the best Class A amplifiers topping out at 25 percent. That means that usually, less than one quarter, and often only one-tenth of the power that goes into the amplifier comes out of it in the form of sound.

Class B amplifiers are extremely high in their efficiency, but they have huge levels of distortion which makes them completely impractical. Therefore, there is a design of amplifiers that are AB. This means that they have the low levels of distortion of the Class A amplifiers, with the high efficiency of the Class B amplifiers. These car stereo system amplifiers commonly range between 35 and 55 in their efficiency, but some really good ones can top out at 78.5 percent.

Class D amplifiers have an efficiency of as much as 97 percent, which makes them extremely sought after for car stereo systems. All the classes from C to F have very high efficiency, but that high efficiency results in lower power output available. This is because the high efficiency can limit that the power output that is usefully available. However, one good note of extremely efficient models is that they run much cooler and do not always need to have cooling fans. Less energy loss means less heat loss.

While Class T may seem like a different class of amplifier, it is in fact a trademark of Tripath and its amplifier technologies. It uses Class D amplifiers with a sophisticated control scheme to provide extremely high quality in the audio amplification. They do not use digital signal processing, and instead use an overall loop modulator. It is almost entirely analog and feedback is taken directly from the switching node rather than through a filtered output, and the higher order loop provides a much higher loop gain at high audio frequencies.
The future of the Class T amplifier is in doubt since Tripath filed for bankruptcy in 2007.