Audio amplifier
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Mission Cyrus 1 Hi Fi integrated audio amplifier |
An
audio amplifier is an
electronic amplifier that works with audio frequencies (generally 20
hertz to 20,000 hertz). It is the final stage in the audio playback chain and its purpose is to amplify the electrical audio signal from its preceding stage to a level that can drive the
loudspeaker(s). The preceding stages are low power audio amplifiers which perform tasks like
pre-amplification,
equalization,
tone control,
mixing/effects, etc or audio sources like
record players,
CD players,
cassette players, etc. By "low power" it is meant that the signals are usually limited to those required to drive
headphones (less than 500 mW).
While the input
signal may be only a few hundred
millivolts, the power amplifier's output may have a
power of many
watts.
Early audio amplifiers were based on
vacuum tubes (also known as "valves"). Most modern audio amplifiers are based on solid state devices like
transistors,
FETs and
MOSFETs, but there are still aficionados who prefer tube based amplifiers, as they have a 'warmer' sound due to a more linear V/I characteristic. Audio amplifiers based on transistors became practical with the wide availability of inexpensive transistors in the late
1960s.
Important applications include
public address systems, home and car
sound systems. The
sound card in a
personal computer contains several audio amplifiers (depending on number of channels), as does every stereo or home-theatre system.
Key design parameters for audio amplifiers are
frequency response,
gain,
noise, and
distortion. These are interdependent, increasing gain often leads to undesirable increases in noise and distortion. While
negative feedback actually reduces the gain, it also reduces noise, oscillation and distortion.
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Electronic amplifier*
Valve amplifier*
Valve sound*
Public address*
Tone control circuits"Circuits" by Ceapa and Constantin.
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Commlinx collection of audio amplifier shematics
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Discover Circuits DIY audio amplifiers
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Introduction to Power Amplifiers at
Sweetwater.com
