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A Brief Primer For Audio Amplifiers

None of modern stereo systems would be doable lacking the aid of today’s mini audio amps which strive to satisfy higher and higher demands concerning power and music fidelity. It is tough to select an amp given the big range of models and concepts. I am going to explain some of the most common amplifier designs including “tube amplifiers”, “linear amplifiers”, “class-AB” and “class-D” as well as “class-T amplifiers” to help you comprehend some of the terms normally utilized by amplifier makers. This essay should also help you figure out what topology is best for your precise application.

Simply put, the principle of an audio amp is to convert a low-power music signal into a high-power audio signal. The high-power signal is big enough to drive a loudspeaker sufficiently loud. The type of element used to amplify the signal depends on what amp topology is utilized. Some amplifiers even make use of several types of elements. Generally the following parts are utilized: tubes, bipolar transistors and FETs. A couple of decades ago, the most widespread kind of audio amplifier were tube amps. Tube amps utilize 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 converted into a high-level signal. Tubes, though, are nonlinear in their behavior and will introduce a rather large level of higher harmonics or distortion. Today, tube amps still have many followers. The main reason is that the distortion that tubes bring about are frequently perceived as “warm” or “pleasant”. Solid state amplifiers with low distortion, on the other hand, are perceived as “cold”.

A disadvantage of tube amps is their low power efficiency. In other words, most of the power consumed by the amp is wasted as heat instead of being transformed into audio. Therefore tube amplifiers are going to run hot and require enough cooling. Tube amplifiers, however, a fairly costly to manufacture and as a result tube amplifiers have mostly been replaced with amplifiers utilizing transistor elements which are less expensive to build.

The first generation types of solid state amplifiers are often known as “Class-A” amps. Solid-state amplifiers employ a semiconductor rather than a tube to amplify the signal. Regularly bipolar transistors or FETs are being used. The working principle of class-A amps is quite similar to that of tube amps. The main difference is that a transistor is being used as opposed to the tube for amplifying the music signal. The amplified high-level signal is sometimes fed back in order to minimize harmonic distortion. In terms of harmonic distortion, class-A amps rank highest amid all types of music amplifiers. These amps 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 essential. Yet, similar to tube amps, class-A amps have extremely low power efficiency and the majority of the energy is wasted. Class-AB amplifiers improve on the efficiency of class-A amps. They utilize a number of transistors in order to split up the large-level signals into two separate regions, each of which can be amplified more efficiently. Because of the larger efficiency, class-AB amps do not need the same number of heat sinks as class-A amps. Therefore they can be made lighter and less costly. Nonetheless, this topology adds some non-linearity or distortion in the region where the signal switches between those regions. As such class-AB amps typically have larger distortion than class-A amplifiers.

To further improve the audio efficiency, “class-D” amps employ a switching stage that is continually switched between 2 states: on or off. None of these 2 states dissipates energy within the transistor. Therefore, class-D amps regularly are able to achieve power efficiencies beyond 90%. The switching transistor, that is being controlled by a pulse-width modulator generates a high-frequency switching component which has to be removed from the amplified signal by utilizing a lowpass filter. The switching transistor and in addition the pulse-width modulator frequently exhibit fairly big non-linearities. As a consequence, the amplified signal will have some distortion. Class-D amplifiers by nature have higher audio distortion than other types of audio amplifiers. To solve the dilemma of large music distortion, modern switching amplifier designs incorporate feedback. The amplified signal is compared with the original low-level signal and errors are corrected. One type of audio amplifiers which makes use of this type of feedback is called “class-T” or “t amplifier”. Class-T amps feed back the high-level switching signal to the audio signal processor for comparison. These amplifiers have small music distortion and can be manufactured extremely small.

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