Electronic amplifier in the context of Power amplifier

In radio communications, a radio receiver, also known as a receiver, a wireless, or simply a radio, is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. The antenna intercepts radio waves (electromagnetic waves of radio frequency) and converts them to tiny alternating currents which are applied to the receiver, and the receiver extracts the desired information. The receiver uses electronic filters to separate the desired radio frequency signal from all the other signals picked up by the antenna, an electronic amplifier to increase the power of the signal for further processing, and finally recovers the desired information through demodulation.

Radio receivers are essential components of all systems based on radio technology. The information produced by the receiver may be in the form of sound, video (television), or digital data. A radio receiver may be a separate piece of electronic equipment, or an electronic circuit within another device. The most familiar type of radio receiver for most people is a broadcast radio receiver, which reproduces sound transmitted by radio broadcasting stations, historically the first mass-market radio application. A broadcast receiver is commonly called a "radio". However radio receivers are very widely used in other areas of modern technology, in televisions, cell phones, wireless modems, radio clocks and other components of communications, remote control, and wireless networking systems.

An instrument amplifier is an electronic amplifier that converts the often barely audible or purely electronic signal of a musical instrument into a larger electronic signal to feed to a loudspeaker. An instrument amplifier is used with musical instruments such as an electric guitar, an electric bass, electric organ, electric piano, synthesizers and drum machine to convert the signal from the pickup (with guitars and other string instruments and some keyboards) or other sound source (e.g, a synthesizer's signal) into an electronic signal that has enough power, produced by a power amplifier, to drive one or more loudspeaker that can be heard by the performers and audience.

Combination (combo) amplifiers include a preamplifier, a power amplifier, tone controls, and one or more speakers in a cabinet, a housing or box usually made of wood. Instrument amplifiers for some instruments are also available without an internal speaker; these amplifiers, called heads, must plug into one or more separate speaker cabinets. Instrument amplifiers also have features that let the performer modify the signal's tone, such as changing the equalization (adjusting bass and treble tone) or adding electronic effects such as intentional distortion or overdrive, reverb or chorus effect.

A guitar amplifier (or amp) is an electronic device or system that strengthens the electrical signal from a pickup on an electric guitar, bass guitar, or acoustic guitar so that it can produce sound through one or more loudspeakers, which are typically housed in a wooden cabinet. A guitar amplifier may be a standalone wood or metal cabinet that contains only the power amplifier (and preamplifier) circuits, requiring the use of a separate speaker cabinet–or it may be a combo amplifier, which contains both the amplifier and one or more speakers in a wooden cabinet. There is a wide range of sizes and power ratings for guitar amplifiers, from small, lightweight practice amplifiers with a single 6-inch speaker and a 10-watt amp to heavy combo amps with four 10-inch or four 12-inch speakers and a 100-watt amplifier, which are loud enough to use in a nightclub or bar performance.

Guitar amplifiers can also modify an instrument's tone by emphasizing or de-emphasizing certain frequencies, using equalizer controls, which function the same way as the bass and treble knobs on a home stereo, and by adding electronic effects; distortion (also called overdrive) and reverb are commonly available as built-in features. The input of modern guitar amplifiers is a 1/4" jack, which is fed a signal from an electro-magnetic pickup (from an electric guitar) or a piezoelectric pickup (usually from an acoustic guitar) using a patch cord, or a wireless transmitter. For electric guitar players, their choice of amp and the settings they use on the amplifier are a key part of their signature tone or sound. Some guitar players are longtime users of a specific amp brand or model. Guitarists may also use external effects pedals to alter the sound of their tone before the signal reaches the amplifier.

A transistor is a semiconductor device used to amplify or switch electrical signals and power. It is one of the basic building blocks of modern electronics. It is composed of semiconductor material, usually with at least three terminals for connection to an electronic circuit. A voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Some transistors are packaged individually, but many more in miniature form are found embedded in integrated circuits. Because transistors are the key active components in practically all modern electronics, many people consider them one of the 20th century's greatest inventions.

Physicist Julius Edgar Lilienfeld proposed the concept of a field-effect transistor (FET) in 1925, but it was not possible to construct a working device at that time. The first working device was a point-contact transistor invented in 1947 by physicists John Bardeen, Walter Brattain, and William Shockley at Bell Labs who shared the 1956 Nobel Prize in Physics for their achievement. The most widely used type of transistor, the metal–oxide–semiconductor field-effect transistor (MOSFET), was invented at Bell Labs between 1955 and 1960. Transistors revolutionized the field of electronics and paved the way for smaller and cheaper radios, calculators, computers, and other electronic devices.

An audio power amplifier (or power amp) amplifies low-power electronic audio signals, such as the signal from a radio receiver or an electric guitar pickup, to a level that is high enough for driving loudspeakers or headphones. Audio power amplifiers are found in all manner of sound systems including sound reinforcement, public address, home audio systems and musical instrument amplifiers like guitar amplifiers. It is the final electronic stage in a typical audio playback chain before the signal is sent to the loudspeakers.

The preceding stages in such a chain are low-power audio amplifiers which perform tasks like pre-amplification of the signal, equalization, mixing different input signals. The inputs can also be any number of audio sources like record players, CD players, digital audio players and cassette players. Most audio power amplifiers require these low-level inputs, which are line level.

A preamplifier, also known as a preamp, is an electronic amplifier that converts a weak electrical signal into an output signal strong enough to be noise-tolerant and strong enough for further processing, or for sending to a power amplifier and a loudspeaker. Without this, the final signal would be noisy or distorted. They are typically used to amplify signals from analog sensors such as microphones and pickups. Because of this, the preamplifier is often placed close to the sensor to reduce the effects of noise and interference.

A triode is an electronic amplifying vacuum tube (or thermionic valve in British English) consisting of three electrodes inside an evacuated glass envelope: a heated filament or cathode, a grid, and a plate (anode).

Developed from Lee De Forest's 1906 Audion, a partial vacuum tube that added a grid electrode to the thermionic diode (Fleming valve), the triode was the first practical electronic amplifier and the ancestor of other types of vacuum tubes such as the tetrode and pentode. Its invention helped make amplified radio technology and long-distance telephony possible. Triodes were widely used in consumer electronics devices such as radios and televisions until the 1970s, when transistors replaced them. Today, their main remaining use is in high-power RF amplifiers in radio transmitters and industrial RF heating devices. In recent years there has been a resurgence in demand for low power triodes due to renewed interest in tube-type audio equipment by audiophiles who prefer the sound of tube-based electronics.

Street theatre is a form of theatrical performance and presentation in outdoor public spaces without a specific paying audience. These spaces can be anywhere, including shopping centres, car parks, recreational reserves, college or university campus and street corners. They are especially seen in outdoor spaces where there are large numbers of people. Performers range from buskers to organised theatre companies, with the purpose of experimenting with performance spaces, promoting their mainstream work, or being commissioned for events such as street festivals, children's shows, or parades.

The logistics of doing street theatre necessitate simple costumes and props, and often there is little or no amplification of sound, with actors depending on their natural vocal and physical ability. This makes physical theatre, including dance, mime and slapstick, a very popular genre in an outdoor setting. The performances need to be highly visible, loud and simple to follow in order to attract a crowd.

A valve amplifier or tube amplifier is a type of electronic amplifier that uses vacuum tubes to increase the amplitude or power of a signal. Low to medium power valve amplifiers for frequencies below the microwaves were largely replaced by solid state amplifiers in the 1960s and 1970s.Valve amplifiers can be used for applications such as guitar amplifiers, satellite transponders such as DirecTV and GPS, high quality stereo amplifiers, military applications (such as radar) and very high power radio and UHF television transmitters.

A low-noise amplifier (LNA) is an electronic component that amplifies a very low-power signal without significantly degrading its signal-to-noise ratio (SNR). Any electronic amplifier will increase the power of both the signal and the noise present at its input, but the amplifier will also introduce some additional noise. LNAs are designed to minimize that additional noise, by choosing special components, operating points, and circuit topologies. Minimizing additional noise must balance with other design goals such as power gain and impedance matching.

LNAs are found in radio communications systems, amateur radio stations, medical instruments and electronic test equipment. A typical LNA may supply a power gain of 100 (20 decibels (dB)) while decreasing the SNR by less than a factor of two (a 3 dB noise figure (NF)). Although LNAs are primarily concerned with weak signals that are just above the noise floor, they must also consider the presence of larger signals that cause intermodulation distortion.

A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. It is an analog circuit with two inputs ${\displaystyle V_{\text{in}}^{-}}$ and ${\displaystyle V_{\text{in}}^{+}}$ and one output ${\displaystyle V_{\text{out}}}$, in which the output is ideally proportional to the difference between the two voltages:

where ${\displaystyle A}$ is the gain of the amplifier.