A Complete Guide to Different Classes of Amplifiers Leave a comment

In our previous post, we discussed 4 important things to look for when buying an amplifier. In today’s post, we’ll continue the discussion on amplifiers by explaining their different classes.

The electrical characteristics of an amplifier can be distinguished by class, thus known as amplifier classes. It defines the type of amplification used in the amplifier output stage. Adding to this, the output stage comprises of two sub power stages, one to amplify positive signals while the other to amplify negative signals. In simpler terms, the classes describe the topology of an amplifier, i.e., how they function at the core level. It is generally denoted by a letter or two.

Here’s a quick guide to different classes of amplifiers used commonly in home audio devices.

Class A

Class A Amplifiers are the simplest and most commonly used devices compared to other amplifier classes. These amplifiers are considered as the best class because of their low signal distortion levels. They deliver the best sound quality and keeps both the stages (positive and negative) on at all times. They have the highest linearity compared to other counterparts and generate the most heat as power is always present, thus delivering high-quality audio. Power efficiency rate of Class-A Amplifiers is 10-20 percent.

Class B

In Class B Amplifiers, current is pulled and pushed between the two sub-power stages, thus keeping one stage on and the other one off. Broadly speaking, if the input signal is negative, then the positive biased transistor switches off and negative biased transistor switches on whereas if the signal is positive, then the negative biased transistor switches off and positive biased transistor switches on. This arrangement creates a more efficient design, thus increasing its power efficiency rate which is 50% to 75%. However, the continuous on and off switching increases the distortion level.

Class AB

Class AB Amplifiers is a combination of Class A and Class B Amplifiers. It is a hybrid with the best features of both the classes, i.e., both the stages are always on for low-level signals and the stages alternate for high-level signals. Apart from combining the best features of Class A and B, this class eliminates their drawbacks as well by increasing the power efficiency and decreasing the distortion level. Currently, Class AB is among the most common types of audio power amplifier design.

Class D

Class D Amplifiers are at the top of the power efficiency rate, i.e., 90%. They are non-linear switching amplifiers that convert the input signals into a progression of higher voltage output pulses. These pulses go through a low-passive filter to remove unwanted frequency components and then transferred to the speaker. Irrespective of the high-efficiency rate, these amplifiers are not good in terms of sound quality.

The next time you plan to buy an amplifier, go through its class mentioned on the specification sheet. Each class of amplifier has a different electrical characteristic and is used for different purposes. Consult an electronic professional to gather more information on the classification of amplifiers before buying one.