Audio amplifiers are at the very heart of every home theater system. As the quality and output power requirements of today's loudspeakers increase, so do the demands of audio amps. It is hard to pick an amplifier given the large number of models and designs. I will explain some of the most common amplifier designs such as "tube amps", "linear amps", "class-AB" and "class-D" as well as "class-t amps" to help you understand some of the terms commonly used by amplifier manufacturers. This guide should also help you figure out which topology is ideal for your particular application.
The basic operating principle of an audio amp is fairly straightforward. An audio amp will take a low-level audio signal. This signal usually comes from a source with a fairly high impedance. It then converts this signal into a large-level signal. This large-level signal can also drive speakers with low impedance. The type of element used to amplify the signal depends on which amplifier architecture is used. Some amps even use several types of elements. Typically the following parts are used: tubes, bipolar transistors and FETs.
Tube amplifiers used to be common a few decades ago. A tube is able to control the current flow according to a control voltage which is connected to the tube. Unfortunately, tube amplifiers have a fairly high amount of distortion. Technically speaking, tube amplifiers will introduce higher harmonics into the signal. However, this characteristic of tube amps still makes these popular. Many people describe tube amps as having a warm sound versus the cold sound of solid state amps.
Another drawback of tube amps, though, is the low power efficiency. The majority of power which tube amps consume is being dissipated as heat and only a fraction is being converted into audio power. Also, tubes are quite expensive to make. Thus tube amps have mostly been replaced by solid-state amps which I will look at next.
Solid-state amps use a semiconductor elements, such as a bipolar transistor or FET in place of the tube and the earliest type is known as "class-A" amps. The working principle of class-A amps is very similar to that of tube amps. The main difference is that a transistor is being used in place of the tube for amplifying the audio signal. The amplified high-level signal is sometimes fed back in order to minimize harmonic distortion. If you require an ultra-low distortion amplifier then you might want to investigate class-A amps since they offer amongst the lowest distortion of any audio amps. However, similar to tube amps, class-A amps have very low power efficiency and most of the energy is wasted.
To improve on the low efficiency of class-A amps, class-AB amps employ a series of transistors which each amplify a separate area, each of which being more efficient than class-A amps. Due to the higher efficiency, class-AB amps do not require the same amount of heat sinks as class-A amps. Therefore they can be made lighter and cheaper. When the signal transitions between the two separate regions, however, some amount of distortion is being generated, thus class-AB amps will not achieve the same audio fidelity as class-A amps.
To further improve the audio efficiency, "class-D" amps use a switching stage which is constantly switched between two states: on or off. None of these 2 states dissipates power inside the transistor. Therefore, class-D amps 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). 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 simple first-order lowpass is being used. The switching transistor and also the pulse-width modulator usually have fairly large non-linearities. As a result, the amplified signal will contain some distortion. Class-D amps by nature have higher audio distortion than other types of audio amplifiers.
Newer amps incorporate internal audio feedback to minimize the amount of audio distortion. One type of audio amps which uses this type of feedback is known as "class-T" or "t amp". Class-T amps feed back the high-level switching signal to the audio signal processor for comparison. These amps have low audio distortion and can be made extremely small.
The basic operating principle of an audio amp is fairly straightforward. An audio amp will take a low-level audio signal. This signal usually comes from a source with a fairly high impedance. It then converts this signal into a large-level signal. This large-level signal can also drive speakers with low impedance. The type of element used to amplify the signal depends on which amplifier architecture is used. Some amps even use several types of elements. Typically the following parts are used: tubes, bipolar transistors and FETs.
Tube amplifiers used to be common a few decades ago. A tube is able to control the current flow according to a control voltage which is connected to the tube. Unfortunately, tube amplifiers have a fairly high amount of distortion. Technically speaking, tube amplifiers will introduce higher harmonics into the signal. However, this characteristic of tube amps still makes these popular. Many people describe tube amps as having a warm sound versus the cold sound of solid state amps.
Another drawback of tube amps, though, is the low power efficiency. The majority of power which tube amps consume is being dissipated as heat and only a fraction is being converted into audio power. Also, tubes are quite expensive to make. Thus tube amps have mostly been replaced by solid-state amps which I will look at next.
Solid-state amps use a semiconductor elements, such as a bipolar transistor or FET in place of the tube and the earliest type is known as "class-A" amps. The working principle of class-A amps is very similar to that of tube amps. The main difference is that a transistor is being used in place of the tube for amplifying the audio signal. The amplified high-level signal is sometimes fed back in order to minimize harmonic distortion. If you require an ultra-low distortion amplifier then you might want to investigate class-A amps since they offer amongst the lowest distortion of any audio amps. However, similar to tube amps, class-A amps have very low power efficiency and most of the energy is wasted.
To improve on the low efficiency of class-A amps, class-AB amps employ a series of transistors which each amplify a separate area, each of which being more efficient than class-A amps. Due to the higher efficiency, class-AB amps do not require the same amount of heat sinks as class-A amps. Therefore they can be made lighter and cheaper. When the signal transitions between the two separate regions, however, some amount of distortion is being generated, thus class-AB amps will not achieve the same audio fidelity as class-A amps.
To further improve the audio efficiency, "class-D" amps use a switching stage which is constantly switched between two states: on or off. None of these 2 states dissipates power inside the transistor. Therefore, class-D amps 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). 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 simple first-order lowpass is being used. The switching transistor and also the pulse-width modulator usually have fairly large non-linearities. As a result, the amplified signal will contain some distortion. Class-D amps by nature have higher audio distortion than other types of audio amplifiers.
Newer amps incorporate internal audio feedback to minimize the amount of audio distortion. One type of audio amps which uses this type of feedback is known as "class-T" or "t amp". Class-T amps feed back the high-level switching signal to the audio signal processor for comparison. These amps have low audio distortion and can be made extremely small.
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You can get additional information regarding t amp models as well as stereo amplifier from Amphony's website.
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