Power amplifiers are at the very heart of each home theater system. As the quality and output power requirements of today's speakers increase, so do the requirements of stereo amplifiers. It is challenging to choose an amplifier given the big number of styles and concepts. I am going to explain a few of the most popular amplifier designs like "tube amplifiers", "linear amps", "class-AB" and "class-D" as well as "class-T amps" to help you understand a few of the terms regularly used by amp suppliers. This guide should also help you figure out what topology is ideal for your precise application.
An audio amplifier will convert a low-level music signal that often originates from a high-impedance source into a high-level signal that may drive a loudspeaker with a low impedance. The kind of element utilized to amplify the signal depends on which amp topology is used. Some amps even employ several types of elements. Typically the following parts are used: tubes, bipolar transistors in addition to FETs.
A downside of tube amplifiers is their small power efficiency. In other words, most of the energy consumed by the amp is wasted as heat rather than being converted into music. Thus tube amps will run hot and need sufficient cooling. Yet an additional downside is the high price tag of tubes. This has put tube amplifiers out of the ballpark for a lot of consumer devices. Consequently, the bulk of audio products today employs solid state amplifiers. I am going to explain solid state amps in the next sections.
Solid state amps replace the tube with semiconductor elements, generally bipolar transistors or FETs. The first type of solid-state amplifiers is often known as class-A amplifiers. In class-A amps a transistor controls the current flow according to a small-level signal. Several amps employ a feedback mechanism in order to minimize the harmonic distortion. If you need an ultra-low distortion amp then you may wish to explore class-A amplifiers as they provide amongst the smallest distortion of any audio amplifiers. However, similar to tube amps, class-A amps have extremely small power efficiency and most of the power is wasted.
Solid state amplifiers replace the tube with semiconductor elements, typically bipolar transistors or FETs. The first kind of solid-state amps is called class-A amps. The working principle of class-A amps is very similar to that of tube amps. The key difference is that a transistor is being utilized rather than the tube for amplifying the music signal. The amplified high-level signal is at times fed back to minimize harmonic distortion. 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. Yet, similar to tube amps, class-A amplifiers have very small power efficiency and the majority of the energy is wasted.
To further improve the audio efficiency, "class-D" amps utilize a switching stage which is constantly switched between 2 states: on or off. None of these two states dissipates energy within the transistor. Therefore, class-D amplifiers frequently 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). Standard 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. Normally a straightforward first-order lowpass is being used. Both the pulse-width modulator and the transistor have non-linearities which result in class-D amplifiers exhibiting larger audio distortion than other types of amplifiers.
More recent audio amps include some kind of mechanism to reduce distortion. One method is to feed back the amplified audio signal to the input of the amplifier to compare with the original signal. The difference signal is then used in order to correct the switching stage and compensate for the nonlinearity. A well-known topology that makes use of this kind of feedback is known as "class-T". Class-T amps 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. Thus t amplifiers can be made extremely small and still achieve high audio fidelity.
An audio amplifier will convert a low-level music signal that often originates from a high-impedance source into a high-level signal that may drive a loudspeaker with a low impedance. The kind of element utilized to amplify the signal depends on which amp topology is used. Some amps even employ several types of elements. Typically the following parts are used: tubes, bipolar transistors in addition to FETs.
A downside of tube amplifiers is their small power efficiency. In other words, most of the energy consumed by the amp is wasted as heat rather than being converted into music. Thus tube amps will run hot and need sufficient cooling. Yet an additional downside is the high price tag of tubes. This has put tube amplifiers out of the ballpark for a lot of consumer devices. Consequently, the bulk of audio products today employs solid state amplifiers. I am going to explain solid state amps in the next sections.
Solid state amps replace the tube with semiconductor elements, generally bipolar transistors or FETs. The first type of solid-state amplifiers is often known as class-A amplifiers. In class-A amps a transistor controls the current flow according to a small-level signal. Several amps employ a feedback mechanism in order to minimize the harmonic distortion. If you need an ultra-low distortion amp then you may wish to explore class-A amplifiers as they provide amongst the smallest distortion of any audio amplifiers. However, similar to tube amps, class-A amps have extremely small power efficiency and most of the power is wasted.
Solid state amplifiers replace the tube with semiconductor elements, typically bipolar transistors or FETs. The first kind of solid-state amps is called class-A amps. The working principle of class-A amps is very similar to that of tube amps. The key difference is that a transistor is being utilized rather than the tube for amplifying the music signal. The amplified high-level signal is at times fed back to minimize harmonic distortion. 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. Yet, similar to tube amps, class-A amplifiers have very small power efficiency and the majority of the energy is wasted.
To further improve the audio efficiency, "class-D" amps utilize a switching stage which is constantly switched between 2 states: on or off. None of these two states dissipates energy within the transistor. Therefore, class-D amplifiers frequently 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). Standard 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. Normally a straightforward first-order lowpass is being used. Both the pulse-width modulator and the transistor have non-linearities which result in class-D amplifiers exhibiting larger audio distortion than other types of amplifiers.
More recent audio amps include some kind of mechanism to reduce distortion. One method is to feed back the amplified audio signal to the input of the amplifier to compare with the original signal. The difference signal is then used in order to correct the switching stage and compensate for the nonlinearity. A well-known topology that makes use of this kind of feedback is known as "class-T". Class-T amps 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. Thus t amplifiers can be made extremely small and still achieve high audio fidelity.
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