Demands concerning audio power and audio fidelity of today’s speakers and home theater systems are constantly growing. At the heart of these systems is the music amplifier. Latest small stereo amplifiers have to perform well enough to satisfy those ever increasing requirements. There is a huge quantity of amplifier concepts and models. All of these vary in terms of performance. I am going to describe some of the most common amp terms such as “class-A”, “class-D” and “t amps” to help you figure out which of these amplifiers is ideal for your application. In addition, after understanding this guide you should be able to comprehend the amplifier specifications that producers publish.
Simply put, the purpose of an audio amplifier is to translate a low-power audio signal into a high-power audio signal. The high-power signal is large enough to drive a loudspeaker sufficiently loud. Depending on the type of amp, one of several types of elements are used in order to amplify the signal like tubes as well as transistors.
Tube amps were commonly used a number of decades ago and utilize a vacuum tube that controls a high-voltage signal in accordance to a low-voltage control signal. One dilemma with tubes is that they are not very linear while amplifying signals. Aside from the original audio, there will be overtones or higher harmonics present in the amplified signal. For that reason tube amplifiers have fairly high distortion. These days, tube amplifiers still have a lot of followers. The primary reason is that the distortion which tubes bring about are often perceived as “warm” or “pleasant”. Solid state amplifiers with small distortion, on the other hand, are perceived as “cold”.
Also, tube amplifiers have rather low power efficiency and consequently radiate much power as heat. In addition, tubes are pretty costly to produce. Hence tube amps have generally been replaced by solid-state amplifiers which I am going to look at next. Solid-state amplifiers utilize a semiconductor element, like a bipolar transistor or FET rather than the tube and the first sort is known as “class-A” amps. In class-A amps a transistor controls the current flow according to a small-level signal. Several amps use a feedback mechanism to reduce the harmonic distortion. Regarding harmonic distortion, class-A amplifiers rank highest amid all types of power amps. These amplifiers also regularly exhibit quite low noise. As such class-A amps are ideal for quite demanding applications in which low distortion and low noise are vital. Yet, similar to tube amps, class-A amps have extremely low power efficiency and most of the power is wasted.
By utilizing a series of transistors, class-AB amplifiers improve on the small power efficiency of class-A amps. The working area is divided into two separate areas. These two regions are handled by separate transistors. Each of those transistors operates more efficiently than the single transistor in a class-A amplifier. Because of the larger efficiency, class-AB amps do not need the same number of heat sinks as class-A amplifiers. Therefore they can be manufactured lighter and less expensive. Class-AB amplifiers have a downside however. Each time the amplified signal transitions from a region to the other, there will be some distortion created. In other words the transition between those two areas is non-linear in nature. Therefore class-AB amplifiers lack audio fidelity compared with class-A amplifiers.
Class-D amplifiers are able to attain power efficiencies above 90% by utilizing a switching transistor that is continually being switched on and off and thus the transistor itself does not dissipate any heat. The switching transistor, which is being controlled by a pulse-width modulator generates a high-frequency switching component that has to be removed from the amplified signal by making use of a lowpass filter. 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 amp.
In order to solve the problem of high audio distortion, newer switching amp styles incorporate feedback. The amplified signal is compared with the original low-level signal and errors are corrected. “Class-T” amps (also referred to as “t-amplifier”) make use of this sort of feedback mechanism and for that reason can be manufactured very small whilst achieving low audio distortion.