How to Select the Best Audio Amplifier for Your Design

How to Select the Best Audio Amplifier for Your Design

 

An audio amplifier increases the amplitude of a small signal to a useful level, all the while maintaining the smaller signal's detail. This is known as linearity. The greater the amplifier linearity, the more the output signal is a true representation of the input.

With the ever-changing performance requirements for amplifiers in the audio market, there have been many advances in audio amplifier topologies. Consequently, designers must know the types of audio amplifiers available and the characteristics associated with each. This is the only way to ensure that you select the best audio amp for an application. In this tutorial, we examine the most important characteristics of each class of audio amp available today: Class A and Class B, .

Class A Amplifiers

The simplest type of audio amplifiers is Class A. Class A amps have output transistors (Figure 1) that conduct (i.e., do not fully turn off), irrespective of the output signal waveform. Class A is the most linear type of audio amp, but it has low efficiency. Consequently, these amps are used in applications that require high linearity and have ample power available.

Figure 1. A Class A audio amp is typically associated with high linearity but low efficiency.

Class B Amplifiers

Class B amplifiers use a push-pull amplifier topology. The output of a Class B amp incorporates a positive and negative transistor. To replicate the input, each transistor only conducts during half (180°) of the signal waveform (Figure 2). This allows the amp to idle with zero current, thereby increasing efficiency compared to a Class A amp.

There is a trade-off that comes with a Class B amp: the increased efficiency degrades audio quality. This happens because there is a crossover point at which the two transistors transition from the on state to the off state. Class B audio amps are also known to have crossover distortion when handling low-level signals. They are not a good choice for low-power applications.

Figure 2. With a Class B audio amp, the output transistors only conduct during half (180°) of the signal waveform. To amplify the entire signal, two transistors are used, one conducting for positive output signals and the other conducting for negative outputs signals