Most audio amplifiers are linear amplifiers operating in class AB. While negative feedback actually reduces the gain, it also reduces distortion. These are interdependent increasing gain often leads to undesirable increases in noise and distortion. Key design parameters for audio power amplifiers are frequency response, gain, noise, and distortion. Three rack-mounted audio power amplifiers used in a sound reinforcement system.
In the 2010s, there are still audio enthusiasts, musicians (particularly electric guitarists, electric bassists, Hammond organ players and Fender Rhodes electric piano players, among others), audio engineers and music producers who prefer tube-based amplifiers, and what is perceived as a "warmer" tube sound. Many transistor amps use MOSFET devices in their power sections, because their distortion curve is more tube-like. Class-D amplifiers became successful in the mid-1980s when low-cost, fast-switching MOSFETs were made available. Hitachi was the only LDMOS manufacturer between 19, during which time LDMOS was used in audio power amplifiers from manufacturers such as HH Electronics (V-series) and Ashly Audio, and were used for music and public address systems. In 1977, Hitachi introduced the LDMOS (lateral diffused MOS), a type of power MOSFET. JVC, Pioneer Corporation, Sony and Toshiba also began manufacturing amplifiers with power MOSFETs in 1974. Power MOSFETs were soon manufactured by Yamaha for their hi-fi audio amplifiers. The MOSFET, invented by Mohamed Atalla and Dawon Kahng at Bell Labs in 1959, was adapted into a power MOSFET for audio by Jun-ichi Nishizawa at Tohoku University in 1974. Transistor-based amplifiers are lighter in weight, more reliable and require less maintenance than tube amplifiers. Since the 1970s, most modern audio amplifiers are based on solid-state transistors, especially the bipolar junction transistor (BJT) and the metal–oxide–semiconductor field-effect transistor (MOSFET). Early audio power amplifiers were based on vacuum tubes and some of these achieved notably high audio quality (e.g., the Williamson amplifier of 1947–9).Īudio power amplifiers based on transistors became practical with the wide availability of inexpensive transistors in the late 1960s. The triode vacuum amplifier was used to make the first AM radio. The triode was a three terminal device with a control grid that can modulate the flow of electrons from the filament to the plate. The audio amplifier was invented around 1912 by Lee de Forest, made possible by his invention of the first practical amplifying electrical component, the triode vacuum tube (or "valve" in British English) in 1907. While power amplifiers are available in standalone units, typically aimed at the hi-fi audiophile market (a niche market) of audio enthusiasts and sound reinforcement system professionals, most consumer electronics audio products, such as clock radios, boomboxes and televisions have relatively small power amplifiers that are integrated into the product.ĭe Forest's prototype audio amplifier of 1914. While the input signal to an audio power amplifier, such as the signal from an electric guitar, may measure only a few hundred microwatts, its output may be a few watts for small consumer electronics devices, such as clock radios, tens or hundreds of watts for a home stereo system, several thousand watts for a nightclub's sound system or tens of thousands of watts for a large rock concert sound reinforcement system. Most audio power amplifiers require these low-level inputs, which are line level. The inputs can also be any number of audio sources like record players, CD players, digital audio players and cassette players. The preceding stages in such a chain are low power audio amplifiers which perform tasks like pre-amplification of the signal (this is particularly associated with record turntable signals, microphone signals and electric instrument signals from pickups, such as the electric guitar and electric bass), equalization (e.g., adjusting the bass and treble), tone controls, mixing different input signals or adding electronic effects such as reverb. It is the final electronic stage in a typical audio playback chain before the signal is sent to the loudspeakers. Audio power amplifiers are found in all manner of sound systems including sound reinforcement, public address and home audio systems and musical instrument amplifiers like guitar amplifiers. The internal view of a Mission Cyrus 1 Hi Fi integrated audio amplifier (1984) Īn audio power amplifier (or power amp) is an electronic amplifier that amplifies low-power electronic audio signals such as the signal from radio receiver or electric guitar pickup to a level that is high enough for driving loudspeakers or headphones.
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