Preamplifier

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"Preamp" redirects here. For the device used in professional audio, see Microphone preamplifier.
An example of a typical high-end stereo 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:

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