TLDR: An amplifier is an electronic device that makes a signal stronger. It can be used in many different types of equipment, like radios, televisions, and musical instruments.
An amplifier is a device that takes a weak signal and makes it stronger. It does this by using electric power from a power supply to increase the amplitude (or strength) of the signal. The amount of amplification provided by an amplifier is measured by its gain, which is the ratio of the output signal to the input signal. Amplifiers can be categorized based on the frequency of the signal they amplify, such as audio amplifiers for sound signals or RF amplifiers for radio frequency signals. They can also be categorized based on their physical placement in a signal chain, such as preamplifiers that come before other signal processing stages or power amplifiers that provide enough output power for the final use of the signal. Amplifiers can use different types of active devices, like vacuum tubes or transistors, to achieve amplification. They can also be classified based on their function, such as servo amplifiers that actively control the output at a desired level or linear amplifiers that respond to different frequency components independently without generating distortion.
Amplifiers have been used in various applications throughout history. The first practical amplifier was the triode vacuum tube, invented in 1906, which led to the development of the first amplifiers around 1912. Vacuum tubes were used in almost all amplifiers until the 1960s-1970s when transistors replaced them. Today, most amplifiers use transistors, but vacuum tubes are still used in some applications. The development of amplifying vacuum tubes revolutionized electrical technology and made possible long-distance telephone lines, radio broadcasting, audio recording, radar, television, and the first computers. Amplifiers have also been used in specialized applications, such as microwave amplifiers for high power amplification at low microwave frequencies or musical instrument amplifiers to increase the sound level of instruments during performances.
Amplifiers can have different properties, such as gain, bandwidth, efficiency, linearity, noise, and dynamic range. They can also be classified based on the terminal that is common to both the input and output circuit, such as common emitter for bipolar junction transistors or common source for field-effect transistors. Amplifiers can be inverting or non-inverting, depending on whether the output signal is 180 degrees out of phase or in phase with the input signal. They can also be classified based on their function, such as servo amplifiers that actively control the output or linear amplifiers that respond to different frequency components independently without generating distortion.
Overall, amplifiers are essential components in modern electronics and are used in a wide range of applications to increase the strength of signals. They have played a significant role in the development of various technologies and continue to be an important part of electronic equipment today.