None of modern audio products would be doable without the help of modern music amplifiers that attempt to satisfy higher and higher demands regarding power and music fidelity. There is a big quantity of amplifier concepts and models. All of these vary when it comes to performance. I am going to explain some of the most common amplifier terms like “class-A”, “class-D” and “t amps” to help you figure out which of these amplifiers is best for your application. In addition, after reading this article you should be able to understand the amplifier specifications which manufacturers issue.
Simply put, the principle of an audio amp is to translate a low-power audio signal into a high-power audio signal. The high-power signal is big enough to drive a speaker adequately loud. The sort of element utilized to amplify the signal is dependent on which amp architecture is utilized. Some amplifiers even utilize several types of elements. Usually the following parts are used: tubes, bipolar transistors plus FETs.
Tube amplifiers used to be popular a few decades ago. A tube is able to control the current flow in accordance to a control voltage which is attached to the tube. Unfortunately, tube amplifiers have a rather high amount of distortion. Technically speaking, tube amps are going to introduce higher harmonics into the signal. On the other hand, this characteristic of tube amplifiers still makes these popular. Many people describe tube amplifiers as having a warm sound as opposed to the cold sound of solid state amplifiers.
Furthermore, tube amps have quite small power efficiency and thus radiate much power as heat. Yet one more drawback is the high price tag of tubes. This has put tube amplifiers out of the ballpark for a lot of consumer products. Consequently, the majority of audio products today utilizes solid state amps. I will describe solid state amplifiers in the subsequent sections.
Solid-state amps employ a semiconductor element, like a bipolar transistor or FET in place of the tube and the earliest type is often known as “class-A” amps. The working principle of class-A amps is very similar to that of tube amplifiers. The main difference is that a transistor is being used in place 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 lowest distortion and usually 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 just like tube amplifiers class A amplifiers have very small efficiency. As a result these amplifiers need large heat sinks in order to dissipate the wasted energy and are usually fairly large. By utilizing a series of transistors, class-AB amps improve on the small power efficiency of class-A amps. The working region is divided into two distinct regions. These two regions are handled by separate transistors. Each of those transistors operates more efficiently than the single transistor in a class-A amplifier. The larger efficiency of class-AB amplifiers also has 2 other advantages. Firstly, the required amount of heat sinking is minimized. For that reason class-AB amps can be manufactured lighter and smaller. For that reason, class-AB amps can be made cheaper than class-A amplifiers. When the signal transitions between the 2 distinct areas, however, some level of distortion is being created, thus class-AB amps will not achieve the same audio fidelity as class-A amplifiers.
Class-D amps improve on the efficiency of class-AB amplifiers even further by making use of a switching transistor that is continuously being switched on or off. Thus this switching stage hardly dissipates any power and thus the power efficiency of class-D amps generally surpasses 90%. The on-off switching times of the transistor are being controlled by a pulse-with modulator (PWM). Typical switching frequencies are between 300 kHz and 1 MHz. This high-frequency switching signal has to be removed from the amplified signal by a lowpass filter. Typically a straightforward first-order lowpass is being utilized. The switching transistor and also the pulse-width modulator usually have rather large non-linearities. As a consequence, the amplified signal will have some distortion. Class-D amplifiers by nature exhibit higher audio distortion than other types of audio amps.
More modern mini audio amplifiers incorporate some sort of mechanism to minimize distortion. One approach is to feed back the amplified audio signal to the input of the amp to compare with the original signal. The difference signal is subsequently utilized to correct the switching stage and compensate for the nonlinearity. “Class-T” amps (also called “t-amplifier”) use this type of feedback method and for that reason can be manufactured extremely small while attaining small music distortion.
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