None of today’s stereo products would be possible lacking the aid of modern music amplifiers which strive to satisfy higher and higher requirements concerning power and audio fidelity. It is tough to pick an amp given the huge range of models and concepts. I will clarify some of the most popular amplifier designs including “tube amps”, “linear amps”, “class-AB” and “class-D” as well as “class-T amplifiers” to help you comprehend several of the terms commonly used by amp producers. This essay should also help you figure out which topology is best for your particular application.
The basic operating principle of an audio amplifier is rather straightforward. An audio amp is going to take a low-level music signal. This signal generally originates from a source with a comparatively large impedance. It subsequently converts this signal into a large-level signal. This large-level signal may also drive speakers with low impedance. Depending on the type of amp, one of several types of elements are used to amplify the signal including tubes in addition to transistors.
Tube amplifiers used to be popular several decades ago. A tube is able to control the current flow according to a control voltage that is attached to the tube. One problem with tubes is that they are not very linear when amplifying signals. Aside from the original audio, there will be overtones or higher harmonics present in the amplified signal. Hence tube amps have moderately large distortion. These days, tube amps still have a lot of followers. The main reason is that the distortion that tubes cause are often perceived as “warm” or “pleasant”. Solid state amps with low distortion, on the other hand, are perceived as “cold”.
In addition, tube amplifiers have quite low power efficiency and thereby radiate a lot of power as heat. Also, tubes are quite costly to produce. As a result tube amplifiers have mostly been replaced by solid-state amplifiers which I am going to glance at next.
Solid-state amps utilize a semiconductor element, such as a bipolar transistor or FET in place of the tube and the earliest sort is generally known as “class-A” amps. The working principle of class-A amplifiers is quite similar to that of tube amps. The primary difference is that a transistor is being utilized instead of the tube for amplifying the music signal. The amplified high-level signal is at times fed back in order to lessen harmonic distortion. Class-A amps have the smallest distortion and generally also the lowest amount of noise of any amplifier architecture. If you require ultra-low distortion then you should take a closer look at class-A types. The major disadvantage is that similar to tube amps class A amplifiers have very small efficiency. Consequently these amplifiers require large heat sinks to radiate the wasted energy and are typically fairly large.
In order to improve on the small efficiency of class-A amps, class-AB amplifiers make use of a number of transistors that each amplify a distinct area, each of which being more efficient than class-A amps. The larger efficiency of class-AB amplifiers also has 2 other advantages. Firstly, the required number of heat sinking is reduced. Consequently class-AB amps can be made lighter and smaller. For that reason, class-AB amps can be made cheaper than class-A amplifiers. Class-AB amplifiers have a drawback though. Every time the amplified signal transitions from a region to the other, there will be certain distortion created. In other words the transition between those 2 regions is non-linear in nature. Therefore class-AB amps lack audio fidelity compared with class-A amplifiers.
Class-D amps improve on the efficiency of class-AB amps even further by utilizing a switching transistor which is constantly being switched on or off. Thereby this switching stage hardly dissipates any energy and thereby the power efficiency of class-D amps typically surpasses 90%. The on-off switching times of the transistor are being controlled by a pulse-with modulator (PWM). Standard switching frequencies are in the range of 300 kHz and 1 MHz. This high-frequency switching signal has to be removed from the amplified signal by a lowpass filter. Usually a simple first-order lowpass is being used. Due to non-linearities of the pulse-width modulator and the switching transistor itself, class-D amps by nature have amongst the highest audio distortion of any audio amp. To solve the problem of high audio distortion, newer switching amplifier designs include feedback. The amplified signal is compared with the original low-level signal and errors are corrected. A well-known topology which employs this sort of feedback is generally known as “class-T”. Class-T amps or “t amps” attain audio distortion that compares with the audio distortion of class-A amps while at the same time exhibiting the power efficiency of class-D amps. Therefore t amplifiers can be manufactured extremely small and still attain high audio fidelity.