None of today’s stereo products would be doable lacking the help of latest music amplifiers which try to satisfy higher and higher requirements regarding power and audio fidelity. There is a huge amount of amplifier concepts and models. All of these differ in terms of performance. I will describe some of the most widespread amp terms like “class-A”, “class-D” and “t amps” to help you figure out which of these amps is ideal for your application. Moreover, after understanding this essay you should be able to comprehend the amp specs that makers publish. Simply put, the function of an audio amplifier is to translate a low-power audio signal into a high-power music signal. The high-power signal is big enough to drive a loudspeaker sufficiently loud. Depending on the type of amplifier, one of several types of elements are utilized in order to amplify the signal including tubes and transistors.
Tube amps were frequently used a couple of decades ago and employ a vacuum tube that controls a high-voltage signal in accordance to a low-voltage control signal. One dilemma with tubes is that they are not extremely linear while amplifying signals. Aside from the original music, there will be overtones or higher harmonics present in the amplified signal. For that reason tube amps have fairly large distortion. Many people prefer tube amplifiers since those higher harmonics are often perceived as the tube amplifier sounding “warm” or “pleasant”.
One disadvantage of tube amps is their small power efficiency. In other words, most of the power consumed by the amp is wasted as heat as opposed to being converted into music. Therefore tube amplifiers will run hot and need adequate cooling. Tube amps, though, a quite costly to manufacture and thus tube amps have by and large been replaced with amps utilizing transistor elements that are less expensive to manufacture.
Solid-state amps use a semiconductor element, like a bipolar transistor or FET in place of the tube and the first type is called “class-A” amps. In a class-A amp, the signal is being amplified by a transistor which is controlled by the low-level audio signal. Regarding harmonic distortion, class-A amplifiers rank highest among all kinds of audio amps. These amps also typically exhibit very low noise. As such class-A amplifiers are ideal for very demanding applications in which low distortion and low noise are vital. However, similar to tube amplifiers, class-A amps have quite low power efficiency and the majority of the energy is wasted.
In order to improve on the small efficiency of class-A amplifiers, class-AB amplifiers employ a number of transistors that each amplify a distinct area, each of which being more efficient than class-A amps. The higher efficiency of class-AB amplifiers also has 2 other advantages. Firstly, the required amount of heat sinking is reduced. Therefore class-AB amps can be manufactured lighter and smaller. For that reason, class-AB amps can be made cheaper than class-A amplifiers. However, this architecture adds some non-linearity or distortion in the area where the signal switches between those areas. As such class-AB amps normally have higher distortion than class-A amplifiers. Class-D amplifiers improve on the efficiency of class-AB amplifiers even further by using a switching transistor that is constantly being switched on or off. Thus this switching stage barely dissipates any power and as a result the power efficiency of class-D amps frequently surpasses 90%. The switching transistor is being controlled by a pulse-width modulator. The switched large-level signal has to be lowpass filtered to remove the switching signal and recover the audio signal. The switching transistor and also the pulse-width modulator frequently have quite big non-linearities. As a consequence, the amplified signal is going to have some distortion. Class-D amps by nature have larger audio distortion than other kinds of audio amplifiers. Modern amplifiers incorporate internal audio feedback to reduce the amount of audio distortion. One type of small stereo amplifiers which employs this type of feedback is called “class-T” or “t amp”. Class-T amplifiers feed back the high-level switching signal to the audio signal processor for comparison. These amps have low music distortion and can be manufactured extremely small.
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