Audio amplifiers are at the very core of each home theater product. As the quality and output power requirements of today's loudspeakers increase, so do the demands of power amps. It is difficult to select an amp given the big range of models and concepts. I am going to explain some of the most popular amp designs like "tube amplifiers", "linear amplifiers", "class-AB" and "class-D" as well as "class-T amps" to help you comprehend some of the terms frequently used by amp producers. This article should also help you figure out what topology is best for your specific application.
Simply put, the function of an audio amplifier is to convert a low-power music signal into a high-power audio signal. The high-power signal is great enough to drive a loudspeaker sufficiently loud. As a way to do that, an amplifier employs one or more elements that are controlled by the low-power signal to generate a large-power signal. Those elements range from tubes, bipolar transistors to FET transistors.
Furthermore, tube amps have quite small power efficiency and thereby dissipate much power as heat. Yet another downside is the big price tag of tubes. This has put tube amps out of the ballpark for the majority of consumer devices. Consequently, the majority of audio products these days employs solid state amps. I will describe solid state amplifiers in the subsequent paragraphs.
The first generation versions of solid state amplifiers are referred to as "Class-A" amps. Solid-state amplifiers use a semiconductor as opposed to a tube to amplify the signal. Generally bipolar transistors or FETs are being utilized. In class-A amps a transistor controls the current flow according to a small-level signal. A number of amps use a feedback mechanism in order to reduce the harmonic distortion. If you need an ultra-low distortion amplifier then you might want to investigate class-A amps because they offer amongst the lowest distortion of any audio amplifiers. The main downside is that similar to tube amplifiers class A amplifiers have very small efficiency. Because of this these amps need big heat sinks to radiate the wasted energy and are frequently fairly bulky.
By utilizing a series of transistors, class-AB amplifiers improve on the low power efficiency of class-A amplifiers. The operating area is split into two distinct regions. These two areas are handled by separate transistors. Each of those transistors works more efficiently than the single transistor in a class-A amp. As such, class-AB amps are typically smaller than class-A amplifiers. However, this topology adds some non-linearity or distortion in the area where the signal switches between those regions. As such class-AB amplifiers typically have higher distortion than class-A amplifiers.
Class-AB amps improve on the efficiency of class-A amplifiers. They use a series of transistors to split up the large-level signals into 2 distinct regions, each of which can be amplified more efficiently. The larger efficiency of class-AB amplifiers also has 2 further advantages. Firstly, the necessary number of heat sinking is reduced. For that reason class-AB amps can be manufactured lighter and smaller. For that reason, class-AB amps can be manufactured cheaper than class-A amplifiers. When the signal transitions between the two separate regions, though, a certain amount of distortion is being created, thereby class-AB amplifiers will not achieve the same audio fidelity as class-A amps.
To further improve the audio efficiency, "class-D" amplifiers use a switching stage that is constantly switched between two states: on or off. None of these two states dissipates energy within the transistor. As a result, class-D amplifiers regularly are able to attain power efficiencies higher than 90%. The on-off switching times of the transistor are being controlled by a pulse-with modulator (PWM). Usual switching frequencies are in the range of 300 kHz and 1 MHz. This high-frequency switching signal has to be removed from the amplified signal by a lowpass filter. Usually a straightforward first-order lowpass is being utilized. 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. To solve the dilemma of large music distortion, modern switching amp styles include feedback. The amplified signal is compared with the original low-level signal and errors are corrected. A well-known architecture which utilizes this sort of feedback is called "class-T". Class-T amps or "t amps" achieve audio distortion that compares with the audio distortion of class-A amps while at the same time exhibiting the power efficiency of class-D amps. Thus t amplifiers can be made extremely small and still attain high audio fidelity.
Simply put, the function of an audio amplifier is to convert a low-power music signal into a high-power audio signal. The high-power signal is great enough to drive a loudspeaker sufficiently loud. As a way to do that, an amplifier employs one or more elements that are controlled by the low-power signal to generate a large-power signal. Those elements range from tubes, bipolar transistors to FET transistors.
Furthermore, tube amps have quite small power efficiency and thereby dissipate much power as heat. Yet another downside is the big price tag of tubes. This has put tube amps out of the ballpark for the majority of consumer devices. Consequently, the majority of audio products these days employs solid state amps. I will describe solid state amplifiers in the subsequent paragraphs.
The first generation versions of solid state amplifiers are referred to as "Class-A" amps. Solid-state amplifiers use a semiconductor as opposed to a tube to amplify the signal. Generally bipolar transistors or FETs are being utilized. In class-A amps a transistor controls the current flow according to a small-level signal. A number of amps use a feedback mechanism in order to reduce the harmonic distortion. If you need an ultra-low distortion amplifier then you might want to investigate class-A amps because they offer amongst the lowest distortion of any audio amplifiers. The main downside is that similar to tube amplifiers class A amplifiers have very small efficiency. Because of this these amps need big heat sinks to radiate the wasted energy and are frequently fairly bulky.
By utilizing a series of transistors, class-AB amplifiers improve on the low power efficiency of class-A amplifiers. The operating area is split into two distinct regions. These two areas are handled by separate transistors. Each of those transistors works more efficiently than the single transistor in a class-A amp. As such, class-AB amps are typically smaller than class-A amplifiers. However, this topology adds some non-linearity or distortion in the area where the signal switches between those regions. As such class-AB amplifiers typically have higher distortion than class-A amplifiers.
Class-AB amps improve on the efficiency of class-A amplifiers. They use a series of transistors to split up the large-level signals into 2 distinct regions, each of which can be amplified more efficiently. The larger efficiency of class-AB amplifiers also has 2 further advantages. Firstly, the necessary number of heat sinking is reduced. For that reason class-AB amps can be manufactured lighter and smaller. For that reason, class-AB amps can be manufactured cheaper than class-A amplifiers. When the signal transitions between the two separate regions, though, a certain amount of distortion is being created, thereby class-AB amplifiers will not achieve the same audio fidelity as class-A amps.
To further improve the audio efficiency, "class-D" amplifiers use a switching stage that is constantly switched between two states: on or off. None of these two states dissipates energy within the transistor. As a result, class-D amplifiers regularly are able to attain power efficiencies higher than 90%. The on-off switching times of the transistor are being controlled by a pulse-with modulator (PWM). Usual switching frequencies are in the range of 300 kHz and 1 MHz. This high-frequency switching signal has to be removed from the amplified signal by a lowpass filter. Usually a straightforward first-order lowpass is being utilized. 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. To solve the dilemma of large music distortion, modern switching amp styles include feedback. The amplified signal is compared with the original low-level signal and errors are corrected. A well-known architecture which utilizes this sort of feedback is called "class-T". Class-T amps or "t amps" achieve audio distortion that compares with the audio distortion of class-A amps while at the same time exhibiting the power efficiency of class-D amps. Thus t amplifiers can be made extremely small and still attain high audio fidelity.
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