Requirements concerning audio power and audio fidelity of recent loudspeakers and home theater systems are constantly growing. At the core of these systems is the audio amplifier. Latest stereo amplifiers have to perform well enough to satisfy those ever increasing requirements. It is challenging to choose an amplifier given the large number of models and concepts. I am going to describe some of the most common amplifier designs including "tube amplifiers", "linear amplifiers", "class-AB" and "class-D" as well as "class-T amps" to help you understand several of the terms normally utilized by amp makers. This article should also help you figure out which topology is perfect for your particular application.
An audio amp is going to convert a low-level music signal which often comes from a high-impedance source into a high-level signal which can drive a speaker with a low impedance. As a way to do that, an amp utilizes one or more elements which are controlled by the low-power signal to generate a large-power signal. These elements range from tubes, bipolar transistors to FET transistors.
Furthermore, tube amplifiers have fairly low power efficiency and thereby dissipate much power as heat. Yet another disadvantage is the high price tag of tubes. This has put tube amplifiers out of the ballpark for many consumer devices. Consequently, the bulk of audio products today makes use of solid state amps. I will describe solid state amps in the next paragraphs.
The first generation versions of solid state amplifiers are known as "Class-A" amps. Solid-state amplifiers make use of a semiconductor rather than a tube to amplify the signal. Generally bipolar transistors or FETs are being used. 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 at times fed back in order to minimize harmonic distortion. Regarding harmonic distortion, class-A amplifiers rank highest among all kinds of music amplifiers. These amplifiers also usually exhibit very low noise. As such class-A amplifiers are ideal for very demanding applications in which low distortion and low noise are vital. Yet, similar to tube amplifiers, class-A amplifiers have quite low power efficiency and most of the power is wasted.
To improve on the low efficiency of class-A amplifiers, class-AB amplifiers utilize a series of transistors that each amplify a separate area, each of which being more efficient than class-A amps. As such, class-AB amplifiers are usually smaller than class-A amplifiers. Class-AB amplifiers have a disadvantage however. Each time the amplified signal transitions from a region to the other, there will be certain distortion produced. In other words the transition between those two areas is non-linear in nature. Consequently class-AB amps lack audio fidelity compared with class-A amplifiers.
Class-D amps improve on the efficiency of class-AB amps even further by using a switching transistor that is continuously being switched on or off. Thereby this switching stage barely dissipates any energy and as a result the power efficiency of class-D amps usually surpasses 90%. The switching transistor is being controlled by a pulse-width modulator. The switched large-level signal needs to be lowpass filtered to remove the switching signal and recover the audio signal. The switching transistor and also the pulse-width modulator frequently have quite large non-linearities. As a result, the amplified signal is going to contain some distortion. Class-D amplifiers by nature have larger audio distortion than other kinds of audio amps.
In order to solve the problem of high audio distortion, modern switching amp designs incorporate feedback. The amplified signal is compared with the original low-level signal and errors are corrected. "Class-T" amps (also called "t-amplifier") use this kind of feedback method and for that reason can be made extremely small while attaining small audio distortion.
An audio amp is going to convert a low-level music signal which often comes from a high-impedance source into a high-level signal which can drive a speaker with a low impedance. As a way to do that, an amp utilizes one or more elements which are controlled by the low-power signal to generate a large-power signal. These elements range from tubes, bipolar transistors to FET transistors.
Furthermore, tube amplifiers have fairly low power efficiency and thereby dissipate much power as heat. Yet another disadvantage is the high price tag of tubes. This has put tube amplifiers out of the ballpark for many consumer devices. Consequently, the bulk of audio products today makes use of solid state amps. I will describe solid state amps in the next paragraphs.
The first generation versions of solid state amplifiers are known as "Class-A" amps. Solid-state amplifiers make use of a semiconductor rather than a tube to amplify the signal. Generally bipolar transistors or FETs are being used. 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 at times fed back in order to minimize harmonic distortion. Regarding harmonic distortion, class-A amplifiers rank highest among all kinds of music amplifiers. These amplifiers also usually exhibit very low noise. As such class-A amplifiers are ideal for very demanding applications in which low distortion and low noise are vital. Yet, similar to tube amplifiers, class-A amplifiers have quite low power efficiency and most of the power is wasted.
To improve on the low efficiency of class-A amplifiers, class-AB amplifiers utilize a series of transistors that each amplify a separate area, each of which being more efficient than class-A amps. As such, class-AB amplifiers are usually smaller than class-A amplifiers. Class-AB amplifiers have a disadvantage however. Each time the amplified signal transitions from a region to the other, there will be certain distortion produced. In other words the transition between those two areas is non-linear in nature. Consequently class-AB amps lack audio fidelity compared with class-A amplifiers.
Class-D amps improve on the efficiency of class-AB amps even further by using a switching transistor that is continuously being switched on or off. Thereby this switching stage barely dissipates any energy and as a result the power efficiency of class-D amps usually surpasses 90%. The switching transistor is being controlled by a pulse-width modulator. The switched large-level signal needs to be lowpass filtered to remove the switching signal and recover the audio signal. The switching transistor and also the pulse-width modulator frequently have quite large non-linearities. As a result, the amplified signal is going to contain some distortion. Class-D amplifiers by nature have larger audio distortion than other kinds of audio amps.
In order to solve the problem of high audio distortion, modern switching amp designs incorporate feedback. The amplified signal is compared with the original low-level signal and errors are corrected. "Class-T" amps (also called "t-amplifier") use this kind of feedback method and for that reason can be made extremely small while attaining small audio distortion.
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