Audio amplifier in the context of Integrated amplifier

An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It is a two-port electronic circuit that uses electric power from a power supply to increase the amplitude (magnitude of the voltage or current) of a signal applied to its input terminals, producing a proportionally greater amplitude signal at its output. The amount of amplification provided by an amplifier is measured by its gain: the ratio of output voltage, current, or power to input. An amplifier is defined as a circuit that has a power gain greater than one.

An amplifier can be either a separate piece of equipment or an electrical circuit contained within another device. Amplification is fundamental to modern electronics, and amplifiers are widely used in almost all electronic equipment. Amplifiers can be categorized in different ways. One is by the frequency of the electronic signal being amplified. For example, audio amplifiers amplify signals of less than 20 kHz, radio frequency (RF) amplifiers amplify frequencies in the range between 20 kHz and 300 GHz, and servo amplifiers and instrumentation amplifiers may work with very low frequencies down to direct current. Amplifiers can also be categorized by their physical placement in the signal chain; a preamplifier may precede other signal processing stages, for example, while a power amplifier is usually used after other amplifier stages to provide enough output power for the final use of the signal. The first practical electrical device which could amplify was the triode vacuum tube, invented in 1906 by Lee de Forest, which led to the first amplifiers around 1912. Today most amplifiers use transistors.

National Semiconductor Corporation was an American semiconductor manufacturer, which specialized in analog devices and subsystems, formerly headquartered in Santa Clara, California. The company produced power management integrated circuits, display drivers, audio and operational amplifiers, communication interface products and data conversion solutions. National's key markets included wireless handsets, displays and a variety of broad electronics markets, including medical, automotive, industrial and test and measurement applications.

On September 23, 2011, the company formally became part of Texas Instruments as the "Silicon Valley" division.

Line level is the specified strength of an audio signal used to transmit analog sound between audio components such as CD and DVD players, television sets, audio amplifiers, and mixing consoles.

Generally, line-level signals sit in the middle of the hierarchy of signal levels in audio engineering. There are weaker signals, such as those from microphones (Mic Level/Microphone Level) and instrument pickups (Instrument Level), and stronger signals, such as those used to drive headphones and loudspeakers (Speaker Level). The "strength" of these various signals does not necessarily refer to the output voltage of the source device; it also depends on its output impedance and output power capability.

Audio equipment refers to devices that reproduce, record, or process sound. This includes microphones, radio receivers, AV receivers, CD players, tape recorders, amplifiers, mixing consoles, effects units, headphones, and speakers.

Audio equipment is widely used in many different scenarios, such as concerts, bars, meeting rooms and the home where there is a need to reproduce, record and enhance sound volume.

A rotary woofer is a subwoofer-style loudspeaker which reproduces very-low-frequency content by using a conventional speaker voice coil's motion to change the pitch (angle) of the blades of an impeller rotating at a constant speed. The pitch of the fan blades is controlled by the audio signal presented to the voice coil, and is able to swing both positive and negative, with respect to a zero-pitch blade position. Since the audio amplifier only changes the pitch of the blades, it takes much less power for a given sound level to drive a rotary woofer than a conventional subwoofer, which uses a moving electromagnet (voice coil) placed within the field of a stationary permanent magnet to move a diaphragm to displace air. Rotary woofers excel at producing sounds below 20 Hz, below the normal hearing range; when installed in a wall of a sealed room, they can produce arbitrarily low frequencies, down to a static pressure differential, by simply compressing or decompressing the air in the sealed room.

Plasma speakers or ionophones are a form of loudspeaker which varies air pressure via an electrical plasma instead of a solid diaphragm. The plasma arc heats the surrounding air causing it to expand. Varying the electrical signal that drives the plasma and connected to the output of an audio amplifier, the plasma size varies which in turn varies the expansion of the surrounding air creating sound waves.

The plasma is typically in the form of a glow discharge and acts as a massless radiating element. The technique is a much later development of physics principles demonstrated by William Duddell's "singing arc" of 1900, and Hermann Theodor Simon published the same phenomenon in 1898.