Demands concerning audio power and audio fidelity of latest speakers and home theater products are continuously increasing. At the heart of these products is the power amplifier. Recent stereo amplifiers have to perform well enough to satisfy those ever growing demands. It is difficult to pick an amplifier given the huge range of types and concepts. I am going to explain some of the most popular amplifier designs such as "tube amps", "linear amplifiers", "class-AB" and "class-D" as well as "class-T amplifiers" to help you comprehend some of the terms regularly utilized by amp producers. This article should also help you figure out what topology is ideal for your specific application.
The main operating principle of an audio amplifier is fairly basic. An audio amplifier is going to take a low-level music signal. This signal usually comes from a source with a rather high impedance. It then translates this signal into a large-level signal. This large-level signal can also drive speakers with low impedance. In order to do that, an amplifier utilizes one or more elements which are controlled by the low-power signal in order to make a large-power signal. Those elements range from tubes, bipolar transistors to FET transistors.
Tube amps used to be popular a couple of 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 quite large amount of higher harmonics or distortion. On the other hand, this characteristic of tube amplifiers still makes these popular. A lot of people describe tube amplifiers as having a warm sound as opposed to the cold sound of solid state amps.
An additional drawback of tube amplifiers, though, is the small power efficiency. The majority of power which tube amps consume is being dissipated as heat and merely a part is being transformed into audio power. Tube amplifiers, on the other hand, a fairly costly to make and as a result tube amps have mostly been replaced with amps employing transistor elements which are less expensive to produce.
Solid state amps replace the tube with semiconductor elements, typically bipolar transistors or FETs. The earliest kind of solid-state amps is called class-A amplifiers. In class-A amps a transistor controls the current flow according to a small-level signal. Several amps use a feedback mechanism to minimize the harmonic distortion. Regarding harmonic distortion, class-A amplifiers rank highest amongst all kinds of power amplifiers. These amplifiers also typically exhibit quite low noise. As such class-A amps are perfect for quite demanding applications in which low distortion and low noise are important. The main downside is that just like tube amplifiers class A amps have extremely small efficiency. Consequently these amps require big heat sinks in order to radiate the wasted energy and are usually rather heavy.
Class-D amps improve on the efficiency of class-AB amplifiers even further by utilizing a switching transistor which is always being switched on or off. Thus this switching stage barely dissipates any power and consequently the power efficiency of class-D amps generally surpasses 90%. The switching transistor, that is being controlled by a pulse-width modulator generates a high-frequency switching component that needs to be removed from the amplified signal by utilizing a lowpass filter. The switching transistor and also the pulse-width modulator frequently exhibit quite big non-linearities. As a result, the amplified signal is going to have some distortion. Class-D amps by nature have higher audio distortion than other kinds of audio amps.
More recent audio amplifiers incorporate some sort of mechanism to reduce distortion. One approach is to feed back the amplified audio signal to the input of the amplifier in order to compare with the original signal. The difference signal is subsequently used to correct the switching stage and compensate for the nonlinearity. A well-known architecture which uses this type of feedback is generally known as "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 offering the power efficiency of class-D amps. Consequently t amps can be manufactured extremely small and yet achieve high audio fidelity.
The main operating principle of an audio amplifier is fairly basic. An audio amplifier is going to take a low-level music signal. This signal usually comes from a source with a rather high impedance. It then translates this signal into a large-level signal. This large-level signal can also drive speakers with low impedance. In order to do that, an amplifier utilizes one or more elements which are controlled by the low-power signal in order to make a large-power signal. Those elements range from tubes, bipolar transistors to FET transistors.
Tube amps used to be popular a couple of 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 quite large amount of higher harmonics or distortion. On the other hand, this characteristic of tube amplifiers still makes these popular. A lot of people describe tube amplifiers as having a warm sound as opposed to the cold sound of solid state amps.
An additional drawback of tube amplifiers, though, is the small power efficiency. The majority of power which tube amps consume is being dissipated as heat and merely a part is being transformed into audio power. Tube amplifiers, on the other hand, a fairly costly to make and as a result tube amps have mostly been replaced with amps employing transistor elements which are less expensive to produce.
Solid state amps replace the tube with semiconductor elements, typically bipolar transistors or FETs. The earliest kind of solid-state amps is called class-A amplifiers. In class-A amps a transistor controls the current flow according to a small-level signal. Several amps use a feedback mechanism to minimize the harmonic distortion. Regarding harmonic distortion, class-A amplifiers rank highest amongst all kinds of power amplifiers. These amplifiers also typically exhibit quite low noise. As such class-A amps are perfect for quite demanding applications in which low distortion and low noise are important. The main downside is that just like tube amplifiers class A amps have extremely small efficiency. Consequently these amps require big heat sinks in order to radiate the wasted energy and are usually rather heavy.
Class-D amps improve on the efficiency of class-AB amplifiers even further by utilizing a switching transistor which is always being switched on or off. Thus this switching stage barely dissipates any power and consequently the power efficiency of class-D amps generally surpasses 90%. The switching transistor, that is being controlled by a pulse-width modulator generates a high-frequency switching component that needs to be removed from the amplified signal by utilizing a lowpass filter. The switching transistor and also the pulse-width modulator frequently exhibit quite big non-linearities. As a result, the amplified signal is going to have some distortion. Class-D amps by nature have higher audio distortion than other kinds of audio amps.
More recent audio amplifiers incorporate some sort of mechanism to reduce distortion. One approach is to feed back the amplified audio signal to the input of the amplifier in order to compare with the original signal. The difference signal is subsequently used to correct the switching stage and compensate for the nonlinearity. A well-known architecture which uses this type of feedback is generally known as "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 offering the power efficiency of class-D amps. Consequently t amps can be manufactured extremely small and yet achieve high audio fidelity.
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