A Brief Explanation Of Audio Amps

Audio amplifiers are at the very heart of each home theater product. As the quality and output power requirements of modern loudspeakers increase, so do the demands of small amplifiers. With the ever growing number of models and design topologies, including "tube amplifiers", "class-A", "class-D" in addition to "t amp" designs, it is getting more and more complex to choose the amp which is best for a specific application. This guide will explain a few of the most popular terms and clarify some of the technical jargon that amplifier makers regularly use.

Simply put, the principle of an audio amp is to translate a low-power music signal into a high-power audio signal. The high-power signal is large enough to drive a loudspeaker adequately loud. As a way to do that, an amplifier employs one or several elements that are controlled by the low-power signal in order to generate a large-power signal. Those elements range from tubes, bipolar transistors to FET transistors.

Tube amps used to be widespread a couple of decades ago. A tube is able to control the current flow according to a control voltage that is connected to the tube. One dilemma with tubes is that they are not very linear while amplifying signals. Aside from the original music, there are going to be overtones or higher harmonics present in the amplified signal. As a result tube amps 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 frequently perceived as "warm" or "pleasant". Solid state amplifiers with low distortion, on the other hand, are perceived as "cold".

A drawback of tube amplifiers is their small power efficiency. In other words, the majority of the power consumed by the amplifier is wasted as heat instead of being transformed into audio. Consequently tube amplifiers will run hot and require enough cooling. Yet one more downside is the high price tag of tubes. This has put tube amps out of the ballpark for many consumer devices. Consequently, the majority of audio products nowadays uses solid state amps. I am going to describe solid state amplifiers in the following paragraphs.

Solid-state amps employ a semiconductor element, like a bipolar transistor or FET rather than the tube and the first kind is often known as "class-A" amps. In a class-A amplifier, the signal is being amplified by a transistor which is controlled by the low-level audio signal. Regarding harmonic distortion, class-A amps rank highest amongst all types of music amps. These amps also usually exhibit very low noise. As such class-A amps are perfect for extremely demanding applications in which low distortion and low noise are essential. The major disadvantage is that similar to tube amplifiers class A amplifiers have extremely low efficiency. As a result these amplifiers require big heat sinks to dissipate the wasted energy and are usually fairly large.

Class-AB amplifiers improve on the efficiency of class-A amplifiers. They make use of a series of transistors in order to break up the large-level signals into two distinct areas, each of which can be amplified more efficiently. Due to the higher efficiency, class-AB amplifiers do not need the same amount of heat sinks as class-A amplifiers. For that reason they can be manufactured lighter and less costly. Though, this architecture adds some non-linearity or distortion in the region where the signal switches between those areas. As such class-AB amps normally have higher distortion than class-A amps.

Class-D amplifiers are able to attain power efficiencies higher than 90% by making use of a switching transistor that is continuously being switched on and off and thereby the transistor itself does not dissipate any heat. 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 needs to be removed from the amplified signal by a lowpass filter. Usually 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 amp.

In order to solve the dilemma of high audio distortion, new switching amplifier styles incorporate feedback. The amplified signal is compared with the original low-level signal and errors are corrected. A well-known architecture which utilizes this kind of feedback is known as "class-T". Class-T amps or "t amps" attain audio distortion which compares with the audio distortion of class-A amps while at the same time exhibiting the power efficiency of class-D amps. Therefore t amplifiers can be made extremely small and still attain high audio fidelity.