Requirements regarding audio power and audio fidelity of today's speakers and home theater products are always increasing. At the center of those systems is the music amp. Recent stereo amplifiers have to perform well enough to meet those ever increasing requirements. It is challenging to choose an amplifier given the huge number of products and designs. I am going to clarify some of the most popular amplifier designs like "tube amplifiers", "linear amps", "class-AB" and "class-D" in addition to "class-T amplifiers" to help you comprehend several of the terms frequently used by amplifier producers. This guide should also help you figure out what topology is best for your particular application. An audio amplifier will translate a low-level music signal that often originates from a high-impedance source into a high-level signal that can drive a speaker with a low impedance. Depending on the type of amp, one of several kinds of elements are utilized in order to amplify the signal including tubes and transistors.
Several decades ago, the most popular type of audio amp were tube amplifiers. Tube amplifiers employ 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. One drawback with tubes is that they are not extremely linear while amplifying signals. Aside from the original audio, there will be overtones or higher harmonics present in the amplified signal. As a result tube amplifiers have rather high distortion. Many people prefer tube amps because these higher harmonics are frequently perceived as the tube amp sounding "warm" or "pleasant".
A number of decades ago, the most popular type of audio amp were tube amplifiers. Tube amplifiers 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. Unfortunately, tube amps have a fairly high level of distortion. Technically speaking, tube amplifiers will introduce higher harmonics into the signal. Many people favor tube amps since these higher harmonics are often perceived as the tube amplifier sounding "warm" or "pleasant". One drawback of tube amplifiers is their small power efficiency. In other words, the majority of the power consumed by the amp is wasted as heat rather than being transformed into audio. For that reason tube amps are going to run hot and need adequate cooling. Furthermore, tubes are rather costly to produce. Therefore tube amplifiers have generally been replaced by solid-state amps which I am going to look at next.
Solid-state amps employ a semiconductor element, like a bipolar transistor or FET as opposed to the tube and the earliest sort is known as "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. Class-A amps have the lowest distortion and typically 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 models. The main disadvantage is that just like tube amplifiers class A amplifiers have extremely small efficiency. Because of this these amplifiers require large heat sinks in order to dissipate the wasted energy and are usually rather heavy.
Class-AB amplifiers improve on the efficiency of class-A amplifiers. They use a number of transistors to break up the large-level signals into two separate areas, each of which can be amplified more efficiently. Because of the higher efficiency, class-AB amps do not need the same number of heat sinks as class-A amps. Therefore they can be made lighter and cheaper. Class-AB amplifiers have a disadvantage though. Each time the amplified signal transitions from one region to the other, there will be some distortion generated. In other words the transition between these 2 regions is non-linear in nature. As a result class-AB amplifiers lack audio fidelity compared with class-A amplifiers.
In order to further improve the audio efficiency, "class-D" amps use a switching stage that is continually switched between 2 states: on or off. None of these 2 states dissipates energy within the transistor. Consequently, class-D amplifiers regularly are able to achieve power efficiencies beyond 90%. The on-off switching times of the transistor are being controlled by a pulse-with modulator (PWM). Usual switching frequencies are between 300 kHz and 1 MHz. This high-frequency switching signal needs to be removed from the amplified signal by a lowpass filter. Normally 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 amplifier.
Newer amps include internal audio feedback to reduce the amount of audio distortion. A well-known topology that makes use of this kind of feedback is generally 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 exhibiting the power efficiency of class-D amps. Therefore t amps can be made extremely small and still attain high audio fidelity.
Several decades ago, the most popular type of audio amp were tube amplifiers. Tube amplifiers employ 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. One drawback with tubes is that they are not extremely linear while amplifying signals. Aside from the original audio, there will be overtones or higher harmonics present in the amplified signal. As a result tube amplifiers have rather high distortion. Many people prefer tube amps because these higher harmonics are frequently perceived as the tube amp sounding "warm" or "pleasant".
A number of decades ago, the most popular type of audio amp were tube amplifiers. Tube amplifiers 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. Unfortunately, tube amps have a fairly high level of distortion. Technically speaking, tube amplifiers will introduce higher harmonics into the signal. Many people favor tube amps since these higher harmonics are often perceived as the tube amplifier sounding "warm" or "pleasant". One drawback of tube amplifiers is their small power efficiency. In other words, the majority of the power consumed by the amp is wasted as heat rather than being transformed into audio. For that reason tube amps are going to run hot and need adequate cooling. Furthermore, tubes are rather costly to produce. Therefore tube amplifiers have generally been replaced by solid-state amps which I am going to look at next.
Solid-state amps employ a semiconductor element, like a bipolar transistor or FET as opposed to the tube and the earliest sort is known as "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. Class-A amps have the lowest distortion and typically 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 models. The main disadvantage is that just like tube amplifiers class A amplifiers have extremely small efficiency. Because of this these amplifiers require large heat sinks in order to dissipate the wasted energy and are usually rather heavy.
Class-AB amplifiers improve on the efficiency of class-A amplifiers. They use a number of transistors to break up the large-level signals into two separate areas, each of which can be amplified more efficiently. Because of the higher efficiency, class-AB amps do not need the same number of heat sinks as class-A amps. Therefore they can be made lighter and cheaper. Class-AB amplifiers have a disadvantage though. Each time the amplified signal transitions from one region to the other, there will be some distortion generated. In other words the transition between these 2 regions is non-linear in nature. As a result class-AB amplifiers lack audio fidelity compared with class-A amplifiers.
In order to further improve the audio efficiency, "class-D" amps use a switching stage that is continually switched between 2 states: on or off. None of these 2 states dissipates energy within the transistor. Consequently, class-D amplifiers regularly are able to achieve power efficiencies beyond 90%. The on-off switching times of the transistor are being controlled by a pulse-with modulator (PWM). Usual switching frequencies are between 300 kHz and 1 MHz. This high-frequency switching signal needs to be removed from the amplified signal by a lowpass filter. Normally 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 amplifier.
Newer amps include internal audio feedback to reduce the amount of audio distortion. A well-known topology that makes use of this kind of feedback is generally 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 exhibiting the power efficiency of class-D amps. Therefore t amps can be made extremely small and still attain high audio fidelity.
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