Stereo amplifiers are at the very heart of each home theater system. As the quality and output power demands of modern loudspeakers increase, so do the demands of mini amps. There is a large quantity of amplifier designs and types. All of these differ regarding performance. I am going to explain a few of the most common amp terms including “class-A”, “class-D” and “t amps” to help you figure out which of these amps is best for your application. Furthermore, after understanding this essay you should be able to comprehend the amp specifications that makers issue.
An audio amplifier is going to translate a low-level audio signal that often comes from a high-impedance source into a high-level signal that can drive a loudspeaker with a low impedance. The kind of element used to amplify the signal is dependent on which amplifier architecture is utilized. Several amplifiers even use several kinds of elements. Typically the following parts are used: tubes, bipolar transistors in addition to FETs.
Several decades ago, the most common type of audio amplifier were tube amps. Tube amps make use of a tube as the amplifying element. The current flow through the tube is controlled by a low-level control signal. Thereby the low-level audio is transformed into a high-level signal. Sadly, tube amps have a somewhat high level of distortion. Technically speaking, tube amps will introduce higher harmonics into the signal. These days, tube amps still have many followers. The most important reason is that the distortion which tubes produce are frequently perceived as “warm” or “pleasant”. Solid state amps with small distortion, on the other hand, are perceived as “cold”.
Another disadvantage of tube amps, however, is the low power efficiency. The majority of power which tube amplifiers use up is being dissipated as heat and merely a part is being converted into audio power. Tube amps, however, a rather expensive to make and therefore tube amplifiers have by and large been replaced with amps utilizing transistor elements which are less expensive to build.
Solid-state amps utilize a semiconductor element, such as a bipolar transistor or FET rather than the tube and the earliest type is generally known as “class-A” amps. In class-A amps a transistor controls the current flow according to a small-level signal. A number of amps make use of a feedback mechanism to reduce the harmonic distortion. Class-A amps have the lowest distortion and typically also the lowest amount of noise of any amplifier architecture. If you need ultra-low distortion then you should take a closer look at class-A types. Though, similar to tube amps, class-A amps have very low power efficiency and most of the power is wasted. To improve on the small efficiency of class-A amps, class-AB amps make use of a number of transistors that each amplify a separate area, each of which being more efficient than class-A amplifiers. The higher efficiency of class-AB amps also has two further advantages. First of all, the necessary amount of heat sinking is minimized. As a result class-AB amplifiers can be manufactured lighter and smaller. For that reason, class-AB amps can be manufactured cheaper than class-A amplifiers. Class-AB amps have a downside 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 those 2 areas is non-linear in nature. As a result class-AB amplifiers lack audio fidelity compared with class-A amps.
Class-D amps are able to attain power efficiencies above 90% by using a switching transistor which is continuously being switched on and off and thus the transistor itself does not dissipate any heat. 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 largest audio distortion of any audio amplifier. Newer amps incorporate internal audio feedback to reduce the amount of audio distortion. “Class-T” amplifiers (also known as “t-amp”) use this kind of feedback method and therefore can be manufactured extremely small whilst attaining small music distortion.
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