None of today's stereo systems would be doable without the aid of latest stereo amps that strive to satisfy higher and higher demands concerning power and music fidelity. With the ever increasing amount of models and design topologies, such as "tube amps", "class-A", "class-D" along with "t amp" designs, it is becoming more and more demanding to pick the amp which is perfect for a particular application. This guide will describe some of the most common terms and clarify some of the technical jargon that amplifier producers regularly employ.
Tube amps were frequently used a number of decades ago and use a vacuum tube which controls a high-voltage signal in accordance to a low-voltage control signal. One dilemma with tubes is that they are not extremely linear when amplifying signals. Aside from the original audio, there are going to be overtones or higher harmonics present in the amplified signal. Consequently tube amplifiers have rather large distortion. Nowadays, tube amplifiers still have a lot of followers. The primary reason is that the distortion which tubes cause are frequently perceived as "warm" or "pleasant". Solid state amplifiers with small distortion, on the other hand, are perceived as "cold".
A number of decades ago, the most common type of audio amplifier were tube amps. Tube amps use a tube as the amplifying element. The current flow through the tube is controlled by a low-level control signal. Thereby the low-level audio is converted into a high-level signal. Regrettably, tube amplifiers have a rather high level of distortion. Technically speaking, tube amplifiers will introduce higher harmonics into the signal. These days, tube amplifiers still have a lot of followers. The most important reason is that the distortion that tubes cause are frequently perceived as "warm" or "pleasant". Solid state amps with low distortion, on the other hand, are perceived as "cold". Furthermore, tube amplifiers have rather small power efficiency and thus dissipate a lot of power as heat. Tube amps, on the other hand, a rather costly to manufacture and thus tube amps have mostly been replaced with amplifiers using transistor elements which are less costly to manufacture.
A different disadvantage of tube amps, though, is the low power efficiency. The majority of power which tube amps use up is being dissipated as heat and merely a fraction is being converted into audio power. Yet another disadvantage is the big price tag of tubes. This has put tube amps out of the ballpark for many consumer devices. Consequently, the majority of audio products nowadays uses solid state amplifiers. I will describe solid state amps in the following sections.
The first generation models of solid state amps are called "Class-A" amps. Solid-state amplifiers employ a semiconductor rather than a tube to amplify the signal. Generally bipolar transistors or FETs are being used. The working principle of class-A amps is quite similar to that of tube amps. The primary difference is that a transistor is being used instead of the tube for amplifying the music signal. The amplified high-level signal is at times fed back to lessen harmonic distortion. Class-A amps have the lowest distortion and generally 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 types. However, similar to tube amps, class-A amplifiers have extremely small power efficiency and most of the energy is wasted.
Class-D amplifiers are able to attain power efficiencies above 90% by employing a switching transistor that is continually being switched on and off and therefore 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 to remove the switching signal and recover the music signal. Both the pulse-width modulator and the transistor have non-linearities which result in class-D amps having bigger music distortion than other types of amplifiers.
Class-D amplifiers are able to achieve power efficiencies higher than 90% by making use of a switching transistor that is continuously being switched on and off and as a result the transistor itself does not dissipate any heat. 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. Generally a straightforward first-order lowpass is being used. The switching transistor and in addition the pulse-width modulator usually have rather big non-linearities. As a consequence, the amplified signal will have some distortion. Class-D amps by nature exhibit higher audio distortion than other types of audio amplifiers. More modern audio amplifiers include some kind of means in order to minimize distortion. One method is to feed back the amplified music signal to the input of the amp in order to compare with the original signal. The difference signal is subsequently used in order to correct the switching stage and compensate for the nonlinearity. "Class-T" amps (also known as "t-amp") use this type of feedback mechanism and thus can be manufactured extremely small while achieving small music distortion.
Tube amps were frequently used a number of decades ago and use a vacuum tube which controls a high-voltage signal in accordance to a low-voltage control signal. One dilemma with tubes is that they are not extremely linear when amplifying signals. Aside from the original audio, there are going to be overtones or higher harmonics present in the amplified signal. Consequently tube amplifiers have rather large distortion. Nowadays, tube amplifiers still have a lot of followers. The primary reason is that the distortion which tubes cause are frequently perceived as "warm" or "pleasant". Solid state amplifiers with small distortion, on the other hand, are perceived as "cold".
A number of decades ago, the most common type of audio amplifier were tube amps. Tube amps use a tube as the amplifying element. The current flow through the tube is controlled by a low-level control signal. Thereby the low-level audio is converted into a high-level signal. Regrettably, tube amplifiers have a rather high level of distortion. Technically speaking, tube amplifiers will introduce higher harmonics into the signal. These days, tube amplifiers still have a lot of followers. The most important reason is that the distortion that tubes cause are frequently perceived as "warm" or "pleasant". Solid state amps with low distortion, on the other hand, are perceived as "cold". Furthermore, tube amplifiers have rather small power efficiency and thus dissipate a lot of power as heat. Tube amps, on the other hand, a rather costly to manufacture and thus tube amps have mostly been replaced with amplifiers using transistor elements which are less costly to manufacture.
A different disadvantage of tube amps, though, is the low power efficiency. The majority of power which tube amps use up is being dissipated as heat and merely a fraction is being converted into audio power. Yet another disadvantage is the big price tag of tubes. This has put tube amps out of the ballpark for many consumer devices. Consequently, the majority of audio products nowadays uses solid state amplifiers. I will describe solid state amps in the following sections.
The first generation models of solid state amps are called "Class-A" amps. Solid-state amplifiers employ a semiconductor rather than a tube to amplify the signal. Generally bipolar transistors or FETs are being used. The working principle of class-A amps is quite similar to that of tube amps. The primary difference is that a transistor is being used instead of the tube for amplifying the music signal. The amplified high-level signal is at times fed back to lessen harmonic distortion. Class-A amps have the lowest distortion and generally 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 types. However, similar to tube amps, class-A amplifiers have extremely small power efficiency and most of the energy is wasted.
Class-D amplifiers are able to attain power efficiencies above 90% by employing a switching transistor that is continually being switched on and off and therefore 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 to remove the switching signal and recover the music signal. Both the pulse-width modulator and the transistor have non-linearities which result in class-D amps having bigger music distortion than other types of amplifiers.
Class-D amplifiers are able to achieve power efficiencies higher than 90% by making use of a switching transistor that is continuously being switched on and off and as a result the transistor itself does not dissipate any heat. 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. Generally a straightforward first-order lowpass is being used. The switching transistor and in addition the pulse-width modulator usually have rather big non-linearities. As a consequence, the amplified signal will have some distortion. Class-D amps by nature exhibit higher audio distortion than other types of audio amplifiers. More modern audio amplifiers include some kind of means in order to minimize distortion. One method is to feed back the amplified music signal to the input of the amp in order to compare with the original signal. The difference signal is subsequently used in order to correct the switching stage and compensate for the nonlinearity. "Class-T" amps (also known as "t-amp") use this type of feedback mechanism and thus can be manufactured extremely small while achieving small music distortion.
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