None of today's audio products would be feasible without the help of recent power amps that strive to satisfy higher and higher demands concerning power and music fidelity. It is challenging to choose an amp given the big number of products and designs. I am going to describe a few of the most common amplifier designs like "tube amplifiers", "linear amplifiers", "class-AB" and "class-D" and also "class-T amps" to help you comprehend some of the terms regularly used by amp makers. This guide should also help you figure out which topology is perfect for your specific application.
The basic operating principle of an audio amp is fairly basic. An audio amplifier is going to take a low-level music signal. This signal usually originates from a source with a rather large impedance. It subsequently translates this signal into a large-level signal. This large-level signal can also drive speakers with low impedance. In order to do that, an amp makes use of one or several elements which are controlled by the low-power signal to create a large-power signal. Those elements range from tubes, bipolar transistors to FET transistors.
Tube amps used to be popular a number of decades ago. A tube is able to control the current flow according to a control voltage that is attached to the tube. One dilemma with tubes is that they are not very linear while amplifying signals. Aside from the original audio, there will be overtones or higher harmonics present in the amplified signal. Consequently tube amplifiers have quite large distortion. Today, tube amplifiers still have a lot of fans. The primary reason is that the distortion which tubes cause are frequently perceived as "warm" or "pleasant". Solid state amps with small distortion, on the other hand, are perceived as "cold".
Solid state amps replace the tube with semiconductor elements, typically bipolar transistors or FETs. The earliest kind of solid-state amplifiers is generally known as class-A amplifiers. In a class-A amplifier, the signal is being amplified by a transistor which is controlled by the low-level audio signal. Class-A amps have the smallest distortion and typically also the smallest amount of noise of any amplifier architecture. If you need ultra-low distortion then you should take a closer look at class-A models. However, similar to tube amps, class-A amplifiers have extremely low power efficiency and the majority of the energy is wasted.
Class-AB amplifiers improve on the efficiency of class-A amps. They employ a series of transistors in order to split up the large-level signals into 2 separate areas, each of which can be amplified more efficiently. As such, class-AB amplifiers are usually smaller 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 some distortion generated. In other words the transition between these two regions is non-linear in nature. Consequently class-AB amps lack audio fidelity compared with class-A amplifiers.
Class-D amps are able to attain power efficiencies above 90% by making use of a switching transistor that is continuously being switched on and off and thus the transistor itself does not dissipate any heat. The switching transistor is being controlled by a pulse-width modulator. The switched large-level signal needs to be lowpass filtered in order to remove the switching signal and recover the music signal. The switching transistor and also the pulse-width modulator frequently have quite big non-linearities. As a result, the amplified signal is going to contain some distortion. Class-D amplifiers by nature have larger audio distortion than other types of audio amps.
More modern audio amps incorporate some sort of mechanism to reduce distortion. One method is to feed back the amplified music signal to the input of the amp to compare with the original signal. The difference signal is then used to correct the switching stage and compensate for the nonlinearity. A well-known topology that uses this sort of feedback is known as "class-T". Class-T amplifiers or "t amps" attain audio distortion which compares with the audio distortion of class-A amps while at the same time having the power efficiency of class-D amps. Thus t amplifiers can be made extremely small and yet attain high audio fidelity.
The basic operating principle of an audio amp is fairly basic. An audio amplifier is going to take a low-level music signal. This signal usually originates from a source with a rather large impedance. It subsequently translates this signal into a large-level signal. This large-level signal can also drive speakers with low impedance. In order to do that, an amp makes use of one or several elements which are controlled by the low-power signal to create a large-power signal. Those elements range from tubes, bipolar transistors to FET transistors.
Tube amps used to be popular a number of decades ago. A tube is able to control the current flow according to a control voltage that is attached to the tube. One dilemma with tubes is that they are not very linear while amplifying signals. Aside from the original audio, there will be overtones or higher harmonics present in the amplified signal. Consequently tube amplifiers have quite large distortion. Today, tube amplifiers still have a lot of fans. The primary reason is that the distortion which tubes cause are frequently perceived as "warm" or "pleasant". Solid state amps with small distortion, on the other hand, are perceived as "cold".
Solid state amps replace the tube with semiconductor elements, typically bipolar transistors or FETs. The earliest kind of solid-state amplifiers is generally known as class-A amplifiers. In a class-A amplifier, the signal is being amplified by a transistor which is controlled by the low-level audio signal. Class-A amps have the smallest distortion and typically also the smallest amount of noise of any amplifier architecture. If you need ultra-low distortion then you should take a closer look at class-A models. However, similar to tube amps, class-A amplifiers have extremely low power efficiency and the majority of the energy is wasted.
Class-AB amplifiers improve on the efficiency of class-A amps. They employ a series of transistors in order to split up the large-level signals into 2 separate areas, each of which can be amplified more efficiently. As such, class-AB amplifiers are usually smaller 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 some distortion generated. In other words the transition between these two regions is non-linear in nature. Consequently class-AB amps lack audio fidelity compared with class-A amplifiers.
Class-D amps are able to attain power efficiencies above 90% by making use of a switching transistor that is continuously being switched on and off and thus the transistor itself does not dissipate any heat. The switching transistor is being controlled by a pulse-width modulator. The switched large-level signal needs to be lowpass filtered in order to remove the switching signal and recover the music signal. The switching transistor and also the pulse-width modulator frequently have quite big non-linearities. As a result, the amplified signal is going to contain some distortion. Class-D amplifiers by nature have larger audio distortion than other types of audio amps.
More modern audio amps incorporate some sort of mechanism to reduce distortion. One method is to feed back the amplified music signal to the input of the amp to compare with the original signal. The difference signal is then used to correct the switching stage and compensate for the nonlinearity. A well-known topology that uses this sort of feedback is known as "class-T". Class-T amplifiers or "t amps" attain audio distortion which compares with the audio distortion of class-A amps while at the same time having the power efficiency of class-D amps. Thus t amplifiers can be made extremely small and yet attain high audio fidelity.
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