Preamplifier

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A preamplifier (preamp) is an electronic amplifier which precedes another amplifier to prepare an electronic signal for further amplification or processing.

[edit] Description

In general, the function of a preamp is to amplify a low level signal (possibly at high impedance) to line-level. A list of common sources would include a pickup, microphone, turntable or other transducer. Equalization and tone control may also be applied.

In a home audio system, the term 'preamplifier' may sometimes be used to describe equipment which merely switches between different line level sources and applies a volume control, so that no actual amplification may be involved. In an audio system the second amplifier is typically a power amplifier (power amp). The preamplifier provides voltage gain (about: 10millivolts to 1volt) but no significant current gain. The power amplifier provides the higher current necessary to drive loudspeakers.

Preamplifiers may be:

• incorporated into the housing or chassis of the amplifier they feed
• in a separate housing
• mounted in other pieces of equipment, such as turntables, microphones and electric basses.
• close to the signal source, remote from the next amplifier -- eg: beside hi-fi system, then feeding into a computer in the home office.

To reduce noise the metal chassis are interconnected, and shielded cables are so connected at the source end only. The use of battery power is good both for audio preamps and amplifiers.

[edit] Examples

• the integrated preamplifier in a foil electret microphone.
• the first stages of an instrument amplifier.
• a stand-alone unit for use in live music and recording studio applications.
• as part of a stand-alone channel strip or channel strip built into an audio mixing desk.
• a masthead amplifier used with television receiver antenna or a satellite receiver dish.

[edit] See also

• Buffer amplifier