Requirements regarding audio power and audio fidelity of recent speakers and home theater systems are always increasing. At the core of these products is the music amp. Latest mini stereo amplifiers have to perform well enough to satisfy those always growing demands. There is a big amount of amp concepts and types. All of these vary when it comes to performance. I will explain a few of the most widespread amplifier terms like “class-A”, “class-D” and “t amps” to help you figure out which of these amplifiers is best for your application. Moreover, after reading this essay you should be able to understand the amplifier specs which makers show.
The main operating principle of an audio amplifier is fairly straightforward. An audio amplifier is going to take a low-level audio signal. This signal regularly originates from a source with a fairly large impedance. It subsequently converts this signal into a large-level signal. This large-level signal may also drive loudspeakers with low impedance. Determined by the type of amp, one of several types of elements are utilized to amplify the signal such as tubes in addition to transistors. Tube amplifiers used to be common a number of decades ago. A tube is able to control the current flow according to a control voltage that is connected to the tube. Tubes, on the other hand, are nonlinear in their behavior and are going to introduce a rather large level of higher harmonics or distortion. Many people prefer tube amplifiers since these higher harmonics are frequently perceived as the tube amplifier sounding “warm” or “pleasant”.
Besides, tube amps have rather small power efficiency and consequently dissipate a lot of power as heat. Also, tubes are fairly expensive to build. Consequently tube amps have generally been replaced by solid-state amps which I will look at next. The first generation models of solid state amps are called “Class-A” amps. Solid-state amplifiers use a semiconductor rather than a tube to amplify the signal. Regularly bipolar transistors or FETs are being utilized. In a class-A amplifier, 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 among all kinds of music amplifiers. These amps also typically exhibit quite 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 amplifiers have very low power efficiency and the majority of the energy is wasted. By using a series of transistors, class-AB amplifiers improve on the small power efficiency of class-A amps. The working area is split into 2 separate regions. These two areas are handled by separate transistors. Each of these transistors works more efficiently than the single transistor in a class-A amplifier. Because of the larger efficiency, class-AB amplifiers do not need the same amount of heat sinks as class-A amplifiers. Therefore they can be manufactured lighter and cheaper. Class-AB amps have a drawback though. Each time the amplified signal transitions from one region to the other, there will be certain distortion generated. In other words the transition between these two regions is non-linear in nature. Consequently class-AB amps lack audio fidelity compared with class-A amplifiers.
In order to further improve the audio efficiency, “class-D” amplifiers utilize a switching stage which is continuously switched between two states: on or off. None of these 2 states dissipates energy inside the transistor. Consequently, class-D amplifiers regularly are able to attain power efficiencies higher than 90%. The switching transistor is being controlled by a pulse-width modulator. The switched large-level signal has to be lowpass filtered in order to remove the switching signal and recover the audio signal. The switching transistor and in addition the pulse-width modulator frequently exhibit fairly big non-linearities. As a consequence, the amplified signal is going to have some distortion. Class-D amps by nature exhibit higher audio distortion than other kinds of audio amps. To solve the dilemma of high music distortion, newer switching amplifier styles include feedback. The amplified signal is compared with the original low-level signal and errors are corrected. One kind of audio amplifiers which employs this type of feedback is known as “class-T” or “t amplifier”. Class-T amps feed back the high-level switching signal to the audio signal processor for comparison. These amps have small music distortion and can be manufactured extremely small.