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Power amplifiers are at the very center of each home theater product. As the quality and output power demands of modern speakers increase, so do the requirements of music amplifiers. With the ever increasing number of models and design topologies, such as "tube amplifiers", "class-A", "class-D" along with "t amp" designs, it is getting more and more complex to select the amplifier which is ideal for a specific application. This guide is going to explain a few of the most common terms and clarify some of the technical jargon that amp makers regularly use. The fundamental operating principle of an audio amp is rather clear-cut. An audio amplifier will take a low-level music signal. This signal generally originates from a source with a rather large impedance. It subsequently translates this signal into a large-level signal. This large-level signal can also drive loudspeakers with small impedance. The sort of element utilized to amplify the signal depends on what amp architecture is utilized. Several amplifiers even employ several kinds of elements. Usually the following parts are utilized: tubes, bipolar transistors and FETs.
Tube amps used to be widespread a few decades ago. A tube is able to control the current flow according to a control voltage which is attached to the tube. Tubes, however, are nonlinear in their behavior and will introduce a fairly large level of higher harmonics or distortion. A lot of people prefer tube amplifiers since these higher harmonics are often perceived as the tube amp sounding "warm" or "pleasant".
Tube amplifiers were commonly used a few decades ago and make use of a vacuum tube which controls a high-voltage signal in accordance to a low-voltage control signal. Tubes, however, are nonlinear in their behavior and are going to introduce a rather large level of higher harmonics or distortion. Though, this characteristic of tube amplifiers still makes these popular. Many people describe tube amplifiers as having a warm sound as opposed to the cold sound of solid state amps. Furthermore, tube amplifiers have quite small power efficiency and as a result radiate much power as heat. Yet one more downside is the big price tag of tubes. This has put tube amps out of the ballpark for a lot of consumer products. Consequently, the majority of audio products today uses solid state amplifiers. I will describe solid state amps in the following paragraphs.
The first generation versions of solid state amps are referred to as "Class-A" amps. Solid-state amplifiers employ a semiconductor instead of a tube to amplify the signal. Generally bipolar transistors or FETs are being utilized. In a class-A amp, the signal is being amplified by a transistor which is controlled by the low-level audio signal. In terms of harmonic distortion, class-A amps rank highest amid all kinds of music amplifiers. These amps also usually exhibit very low noise. As such class-A amps are ideal for extremely demanding applications in which low distortion and low noise are important. Class-A amps, however, waste most of the energy as heat. As a result they generally have large heat sinks and are fairly bulky.
The first generation models of solid state amplifiers are generally known as "Class-A" amps. Solid-state amplifiers utilize a semiconductor instead of a tube to amplify the signal. Generally bipolar transistors or FETs are being used. In class-A amps a transistor controls the current flow according to a small-level signal. Some amps utilize a feedback mechanism to minimize the harmonic distortion. Regarding harmonic distortion, class-A amplifiers rank highest amongst all kinds of audio amplifiers. These amps also typically exhibit very low noise. As such class-A amplifiers are perfect for extremely demanding applications in which low distortion and low noise are crucial. However, similar to tube amplifiers, class-A amps have extremely low power efficiency and the majority of the power is wasted.
Class-AB amplifiers improve on the efficiency of class-A amps. They make use of a series of transistors to break up the large-level signals into two distinct areas, each of which can be amplified more efficiently. As such, class-AB amps are typically smaller than class-A amplifiers. Class-AB amps have a downside however. Each time the amplified signal transitions from one region to the other, there will be certain distortion generated. In other words the transition between those two regions is non-linear in nature. As a result class-AB amplifiers lack audio fidelity compared with class-A amps.
Class-D amplifiers improve on the efficiency of class-AB amplifiers even further by utilizing a switching transistor that is continuously being switched on or off. Thus this switching stage hardly dissipates any power and therefore the power efficiency of class-D amps generally surpasses 90%. The switching transistor is being controlled by a pulse-width modulator. The switched large-level signal has to be lowpass filtered to remove the switching signal and recover the music signal. 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 amp. In order to solve the problem of high audio distortion, new switching amplifier styles incorporate feedback. The amplified signal is compared with the original low-level signal and errors are corrected. One type of audio amplifiers which uses this kind of feedback is called "class-T" or "t amp". Class-T amplifiers feed back the high-level switching signal to the audio signal processor for comparison. These amplifiers exhibit small audio distortion and can be manufactured very small.
Tube amps used to be widespread a few decades ago. A tube is able to control the current flow according to a control voltage which is attached to the tube. Tubes, however, are nonlinear in their behavior and will introduce a fairly large level of higher harmonics or distortion. A lot of people prefer tube amplifiers since these higher harmonics are often perceived as the tube amp sounding "warm" or "pleasant".
Tube amplifiers were commonly used a few decades ago and make use of a vacuum tube which controls a high-voltage signal in accordance to a low-voltage control signal. Tubes, however, are nonlinear in their behavior and are going to introduce a rather large level of higher harmonics or distortion. Though, this characteristic of tube amplifiers still makes these popular. Many people describe tube amplifiers as having a warm sound as opposed to the cold sound of solid state amps. Furthermore, tube amplifiers have quite small power efficiency and as a result radiate much power as heat. Yet one more downside is the big price tag of tubes. This has put tube amps out of the ballpark for a lot of consumer products. Consequently, the majority of audio products today uses solid state amplifiers. I will describe solid state amps in the following paragraphs.
The first generation versions of solid state amps are referred to as "Class-A" amps. Solid-state amplifiers employ a semiconductor instead of a tube to amplify the signal. Generally bipolar transistors or FETs are being utilized. In a class-A amp, the signal is being amplified by a transistor which is controlled by the low-level audio signal. In terms of harmonic distortion, class-A amps rank highest amid all kinds of music amplifiers. These amps also usually exhibit very low noise. As such class-A amps are ideal for extremely demanding applications in which low distortion and low noise are important. Class-A amps, however, waste most of the energy as heat. As a result they generally have large heat sinks and are fairly bulky.
The first generation models of solid state amplifiers are generally known as "Class-A" amps. Solid-state amplifiers utilize a semiconductor instead of a tube to amplify the signal. Generally bipolar transistors or FETs are being used. In class-A amps a transistor controls the current flow according to a small-level signal. Some amps utilize a feedback mechanism to minimize the harmonic distortion. Regarding harmonic distortion, class-A amplifiers rank highest amongst all kinds of audio amplifiers. These amps also typically exhibit very low noise. As such class-A amplifiers are perfect for extremely demanding applications in which low distortion and low noise are crucial. However, similar to tube amplifiers, class-A amps have extremely low power efficiency and the majority of the power is wasted.
Class-AB amplifiers improve on the efficiency of class-A amps. They make use of a series of transistors to break up the large-level signals into two distinct areas, each of which can be amplified more efficiently. As such, class-AB amps are typically smaller than class-A amplifiers. Class-AB amps have a downside however. Each time the amplified signal transitions from one region to the other, there will be certain distortion generated. In other words the transition between those two regions is non-linear in nature. As a result class-AB amplifiers lack audio fidelity compared with class-A amps.
Class-D amplifiers improve on the efficiency of class-AB amplifiers even further by utilizing a switching transistor that is continuously being switched on or off. Thus this switching stage hardly dissipates any power and therefore the power efficiency of class-D amps generally surpasses 90%. The switching transistor is being controlled by a pulse-width modulator. The switched large-level signal has to be lowpass filtered to remove the switching signal and recover the music signal. 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 amp. In order to solve the problem of high audio distortion, new switching amplifier styles incorporate feedback. The amplified signal is compared with the original low-level signal and errors are corrected. One type of audio amplifiers which uses this kind of feedback is called "class-T" or "t amp". Class-T amplifiers feed back the high-level switching signal to the audio signal processor for comparison. These amplifiers exhibit small audio distortion and can be manufactured very small.
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