Amplifier
For guitar amplifier, go to Instrument amplifier
An amplifier can be considered to be any device that uses a small amount of energy to control a larger amount, although the term today usually refers to an electronic amplifier. The relationship of the input to the output of an amplifier — usually expressed as a function of the input frequency — is called the transfer function of the amplifier, and the magnitude of the transfer function is termed the gain.
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Electronic amplifiers
The most common type of amplifier is the electronic amplifier, commonly used in radio and television transmitters and receivers, high-fidelity ("hi-fi") stereo equipment, microcomputers and other electronic digital equipment, and guitar and other instrument amplifiers. Its critical components are active devices, such as vacuum tubes or transistors.
Vacuum tube (valve) amplifiers
In the earlier years of audio, vacuum tubes filled the active device role.
Transistor amplifiers
Most common active devices in transistor amplifiers are bipolar junction transistors (BJTs); metal oxide semiconductor field-effect transistors (MOSFETs) are also used. The essential role of this active element is to magnify an input signal to yield a significantly larger output signal. The amount of magnification (the "forward gain") is determined by the external circuit design as well as the active device.
Operational amplifiers (op-amps)
An operational amplifier is a solid state integrated circuit amplifier which employs external feedback for control of its transfer function or gain
Other amplifier types
There are also mechanical amplifiers, such as the automotive servo used in braking. Relays can be included under the above definition of amplifiers although their transfer function is not linear.(ie they are either open or closed). Another type of amplifier is the fluidic amplifier, based on the fluidic triode.
A magnetic amplifier is a transformer-like device that makes use of the saturation of magnetic materials to produce amplification. It is a non-electronic electrical amplifer with no moving parts. The bandwidth of magnetic amplifiers extends to the tens of kilohertz.
An Amplidyne or Rototrol is a rotating machine like an electrical generator that provides amplification of electrical signals by conversion of mechanical energy to electrical energy.
See also: low noise amplifier, preamplifier, satellite in-line amplifier.da:Forstærker de:Verstärker (Technik) fr:Amplificateur it:Amplificatore ja:アンプ nl:Versterker pl:Wzmacniacz ru:Усилитель звуковых частот sv:förstärkare
External links
- The Audio Circuit - Information on and user reviews of loudspeakers, headphones, amplifiers, and playback equipment.