Audio amps are at the very core of every home theater product. As the quality and output power demands of modern loudspeakers increase, so do the demands of music amps. With the ever growing amount of models and design topologies, like "tube amplifiers", "class-A", "class-D" along with "t amp" designs, it is becoming more and more complex to choose the amplifier which is perfect for a particular application. This guide is going to explain a few of the most common terms and clarify a few of the technical jargon that amplifier makers frequently utilize.
An audio amp will convert a low-level music signal that frequently originates from a high-impedance source into a high-level signal that can drive a speaker with a low impedance. The sort of element used to amplify the signal depends on what amplifier topology is used. A few amps even make use of several types of elements. Typically the following parts are used: tubes, bipolar transistors in addition to FETs.
A couple of decades ago, the most popular type of audio amp were tube amps. Tube amps utilize 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 transformed into a high-level signal. Tubes, however, are nonlinear in their behavior and are going to introduce a rather large level of higher harmonics or distortion. On the other hand, this characteristic of tube amplifiers still makes these popular. A lot of people describe tube amps as having a warm sound versus the cold sound of solid state amplifiers. A downside of tube amplifiers is their low power efficiency. In other words, most of the energy consumed by the amp is wasted as heat as opposed to being transformed into music. For that reason tube amps will run hot and need enough cooling. Yet one more drawback is the big price tag of tubes. This has put tube amplifiers out of the ballpark for a lot of consumer products. Consequently, the bulk of audio products these days makes use of solid state amps. I am going to describe solid state amplifiers in the next paragraphs.
Solid-state amplifiers utilize a semiconductor element, like a bipolar transistor or FET instead of the tube and the earliest type is often known as "class-A" amps. In class-A amps a transistor controls the current flow according to a small-level signal. Several amps make use of a feedback mechanism to reduce the harmonic distortion. Class-A amps have the lowest distortion and typically also the smallest amount of noise of any amplifier architecture. If you require ultra-low distortion then you should take a closer look at class-A types. The main drawback is that similar to tube amps class A amplifiers have very low efficiency. Consequently these amplifiers require large heat sinks to dissipate the wasted energy and are frequently fairly heavy.
Solid-state amplifiers use a semiconductor element, such as a bipolar transistor or FET instead of the tube and the earliest kind is generally known as "class-A" amps. The working principle of class-A amps is quite similar to that of tube amplifiers. 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 to lessen harmonic distortion. Class-A amps have the lowest distortion and typically also the lowest amount of noise of any amplifier architecture. If you need ultra-low distortion then you should take a closer look at class-A types. Class-A amps, though, waste most of the energy as heat. As a result they generally have large heat sinks and are fairly bulky.
Class-D amps are able to attain power efficiencies higher than 90% by utilizing a switching transistor which is continually 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). Usual switching frequencies are in the range of 300 kHz and 1 MHz. This high-frequency switching signal needs to be removed from the amplified signal by a lowpass filter. Generally a simple 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.
In order to further improve the audio efficiency, "class-D" amps utilize a switching stage which is continuously switched between two states: on or off. None of these 2 states dissipates energy inside the transistor. As a result, class-D amplifiers regularly are able to achieve power efficiencies beyond 90%. The switching transistor, which is being controlled by a pulse-width modulator generates a high-frequency switching component that needs to be removed from the amplified signal by making use of a lowpass filter. The switching transistor and in addition the pulse-width modulator usually have rather big non-linearities. As a consequence, the amplified signal will contain some distortion. Class-D amps by nature have larger audio distortion than other types of audio amps. More recent audio amplifiers include some kind of means in order to reduce distortion. One approach is to feed back the amplified audio 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-amplifier") use this sort of feedback method and thus can be made very small whilst achieving small music distortion.
An audio amp will convert a low-level music signal that frequently originates from a high-impedance source into a high-level signal that can drive a speaker with a low impedance. The sort of element used to amplify the signal depends on what amplifier topology is used. A few amps even make use of several types of elements. Typically the following parts are used: tubes, bipolar transistors in addition to FETs.
A couple of decades ago, the most popular type of audio amp were tube amps. Tube amps utilize 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 transformed into a high-level signal. Tubes, however, are nonlinear in their behavior and are going to introduce a rather large level of higher harmonics or distortion. On the other hand, this characteristic of tube amplifiers still makes these popular. A lot of people describe tube amps as having a warm sound versus the cold sound of solid state amplifiers. A downside of tube amplifiers is their low power efficiency. In other words, most of the energy consumed by the amp is wasted as heat as opposed to being transformed into music. For that reason tube amps will run hot and need enough cooling. Yet one more drawback is the big price tag of tubes. This has put tube amplifiers out of the ballpark for a lot of consumer products. Consequently, the bulk of audio products these days makes use of solid state amps. I am going to describe solid state amplifiers in the next paragraphs.
Solid-state amplifiers utilize a semiconductor element, like a bipolar transistor or FET instead of the tube and the earliest type is often known as "class-A" amps. In class-A amps a transistor controls the current flow according to a small-level signal. Several amps make use of a feedback mechanism to reduce the harmonic distortion. Class-A amps have the lowest distortion and typically also the smallest amount of noise of any amplifier architecture. If you require ultra-low distortion then you should take a closer look at class-A types. The main drawback is that similar to tube amps class A amplifiers have very low efficiency. Consequently these amplifiers require large heat sinks to dissipate the wasted energy and are frequently fairly heavy.
Solid-state amplifiers use a semiconductor element, such as a bipolar transistor or FET instead of the tube and the earliest kind is generally known as "class-A" amps. The working principle of class-A amps is quite similar to that of tube amplifiers. 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 to lessen harmonic distortion. Class-A amps have the lowest distortion and typically also the lowest amount of noise of any amplifier architecture. If you need ultra-low distortion then you should take a closer look at class-A types. Class-A amps, though, waste most of the energy as heat. As a result they generally have large heat sinks and are fairly bulky.
Class-D amps are able to attain power efficiencies higher than 90% by utilizing a switching transistor which is continually 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). Usual switching frequencies are in the range of 300 kHz and 1 MHz. This high-frequency switching signal needs to be removed from the amplified signal by a lowpass filter. Generally a simple 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.
In order to further improve the audio efficiency, "class-D" amps utilize a switching stage which is continuously switched between two states: on or off. None of these 2 states dissipates energy inside the transistor. As a result, class-D amplifiers regularly are able to achieve power efficiencies beyond 90%. The switching transistor, which is being controlled by a pulse-width modulator generates a high-frequency switching component that needs to be removed from the amplified signal by making use of a lowpass filter. The switching transistor and in addition the pulse-width modulator usually have rather big non-linearities. As a consequence, the amplified signal will contain some distortion. Class-D amps by nature have larger audio distortion than other types of audio amps. More recent audio amplifiers include some kind of means in order to reduce distortion. One approach is to feed back the amplified audio 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-amplifier") use this sort of feedback method and thus can be made very small whilst achieving small music distortion.
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