Preamplifier

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A preamplifier, also known as a preamp, is an

An ideal preamp will be linear (have a constant gain through its operating range) and have high input impedance (requiring only a minimal amount of current to sense the input signal) and low output impedance (when current is drawn from the output there is minimal change in the output voltage). 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.

Three basic types of preamplifiers are available:

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

In an audio system, they are typically used to amplify signals from analog sensors to

• The integrated preamplifier in a foil electret microphone
• The first stage of an instrument amplifier, the output of which is then sent to the power amplifier. With instrument amplifiers, the preamp is often designed to produce overdrive or distortion effects.
• A stand-alone unit for use in
  live music and recording studio
  applications
• Part of a stand-alone
  mixing desk
• A
  antenna
  (For a receiver far from the antenna, it amplifies the signal and noise from the antenna, reducing the negative effects of the necessary cable length; for an antenna near a receiver, such an amplifier only adds noise.)
• A component in the electronic part of a
  receiver
  dish
• A circuit inside of a hard disk drive or tape player connected to the magnetic heads, or the circuit inside of an optical disc drive (such as CD) which connects to the photodiodes
• A component amplifying the signal from a phonograph cartridge to the line-level input of common power amplifiers
• A switched capacitor circuit used to null the effects of mismatch offset in most CMOS comparator-based flash analog-to-digital converters
• Due to their unique coloration, some preamplifiers can be emulated in software to be used in mixing.

• Low-noise amplifier (LNA)
• Instrumentation amplifier
• Buffer amplifier
• Logarithmic resistor ladder

• Media related to Audio preamplifiers at Wikimedia Commons