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Douglas Harper's Etymology Dictionary
preamplifier

1929, from pre- + amplifier. Shortened form pre-amp is attested from 1957.

Wiktionary
preamplifier

n. a voltage amplifier for amplifying a low-level input signal; its output is the input to a higher-level amplifier

Wikipedia
Preamplifier

A preamplifier (preamp) is an electronic amplifier that prepares a small electrical signal for further amplification or processing. They are typically used to amplify signals from microphones, instrument pickups, and phonographs to line level. Preamplifiers are often integrated into the audio inputs on mixing consoles, DJ mixers, and sound cards. They can also be stand-alone devices.

A preamplifier is often placed close to the sensor to reduce the effects of noise and interference. It is used to boost the signal strength to drive the cable to the main instrument without significantly degrading the signal-to-noise ratio (SNR). The noise performance of a preamplifier is critical. According to Friis's formula, when the gain of the preamplifier is high, the SNR of the final signal is determined by the SNR of the input signal and the noise figure of the preamplifier.

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 (e.g., from 10 mV to 1 V) but no significant current gain. The power amplifier provides the higher current necessary to drive loudspeakers.

Three basic types of preamplifiers are available:

  • current-sensitive preamplifier
  • parasitic-capacitance preamplifier
  • charge-sensitive preamplifier.

Usage examples of "preamplifier".

Manabe muttered that so little power would hardly move the diaphragm, and started tying in a spare preamplifier stage on the input side.

This little model has a preamplifier, a twenty-three-bit analog-to-digital converter with a one hundred and thirty-eight decibel dynamic range.