Preamplifier

"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. 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 Friss' 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.

Description

In general, the function of a preamplifier is to amplify a low-level signal to line-level. A list of common low-level signal sources would include a pickup, microphone, turntable or other transducers. 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 (e.g. from 10 millivolts to 1 volt) 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 within or near the signal source, such as a turntable, microphone or musical instrument.

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.
• The circuit inside of a hard drive connected to the magnetic heads or the circuit inside of CD/DVD drive which connects to the photodiodes.
• A switched capacitor circuit used to null the effects of mismatch offset in most CMOS comparator-based flash analog-to-digital converters

See also

• Low-noise amplifier (LNA)
• Instrumentation amplifier
• Buffer amplifier

External links

• WikiRecording's Guide to Choosing a Microphone Pre-Amp
• Preamplifier.org - An overview of the most common types of preamplifiers.