Demands regarding audio power and audio fidelity of today’s loudspeakers and home theater products are continuously growing. At the center of these products is the music amp. Latest stereo amps have to perform well enough to satisfy these always growing requirements. There is a large amount of amp designs and types. All of these vary when it comes to performance. I will explain a few of the most common amplifier terms including “class-A”, “class-D” and “t amps” to help you figure out which of these amplifiers is best for your application. Additionally, after understanding this guide you should be able to comprehend the amp specifications that producers publish.
Simply put, the use of an audio amplifier is to convert a low-power music signal into a high-power audio signal. The high-power signal is big enough to drive a speaker adequately loud. Determined by the kind of amp, one of several types of elements are used to amplify the signal like tubes and transistors.
An additional disadvantage of tube amps, however, is the small power efficiency. The bulk of power which tube amplifiers use up is being dissipated as heat and only a fraction is being transformed into audio power. Tube amps, though, a rather costly to manufacture and for that reason tube amps have by and large been replaced with amps employing transistor elements that are less expensive to make.
A different downside of tube amps, however, is the low power efficiency. The bulk of power that tube amps use up is being dissipated as heat and merely a portion is being converted into audio power. Tube amplifiers, however, a quite expensive to produce and consequently tube amplifiers have mostly been replaced with amps utilizing transistor elements that are less costly to produce.
Class-AB amps improve on the efficiency of class-A amps. They use a series of transistors in order to split up the large-level signals into 2 separate regions, each of which can be amplified more efficiently. As such, class-AB amplifiers are usually smaller than class-A amps. Nonetheless, this architecture adds some non-linearity or distortion in the area where the signal switches between those regions. As such class-AB amplifiers generally have higher distortion than class-A amps.
Class-D amplifiers improve on the efficiency of class-AB amps even further by making use of a switching transistor that is constantly being switched on or off. Thereby this switching stage hardly dissipates any energy and as a result the power efficiency of class-D amps typically surpasses 90%. The on-off switching times of the transistor are being controlled by a pulse-with modulator (PWM). Standard 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 used. 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 make use of a switching stage that is continually switched between 2 states: on or off. None of these 2 states dissipates energy within the transistor. As a result, class-D amps regularly are able to achieve power efficiencies beyond 90%. The on-off switching times of the transistor are being controlled by a pulse-with modulator (PWM). Typical switching frequencies are between 300 kHz and 1 MHz. This high-frequency switching signal has to be removed from the amplified signal by a lowpass filter. Typically a straightforward 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 largest audio distortion of any audio amp. To solve the problem of high audio distortion, newer switching amplifier styles include feedback. The amplified signal is compared with the original low-level signal and errors are corrected. A well-known topology that employs this type of feedback is called “class-T”. Class-T amps or “t amps” achieve audio distortion which compares with the audio distortion of class-A amps while at the same time offering the power efficiency of class-D amplifiers. Thus t amplifiers can be made extremely small and yet attain high audio fidelity.
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