A preamplifier, also known as a preamp, is an

electronic amplifier An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It may increase the power significantly, or its main effect may be to boost the ...

that converts a weak electrical

signal In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The '' IEEE Transactions on Signal Processing' ...

into an output signal strong enough to be noise-tolerant and strong enough for further processing, or for sending to a power amplifier and a

loudspeaker A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or ...

. Without this, the final signal would be noisy or distorted. They are typically used to amplify signals from analog sensors such as

microphone A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and pub ...

s and pickups. Because of this, the preamplifier is often placed close to the sensor to reduce the effects of

noise Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference aris ...

and interference.

Description

An ideal preamp will be linear (have a constant

gain Gain or GAIN may refer to: Science and technology * Gain (electronics), an electronics and signal processing term * Antenna gain * Gain (laser), the amplification involved in laser emission * Gain (projection screens) * Information gain in d ...

through its operating range), have high

input impedance The input impedance of an electrical network is the measure of the opposition to current ( impedance), both static (resistance) and dynamic ( reactance), into the load network that is ''external'' to the electrical source. The input admittance (the ...

(requiring only a minimal amount of current to sense the input signal) and a 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 Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to the noise power, often expressed in d ...

(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.

Audio systems

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

line level Line level is the specified strength of an audio signal used to transmit analog audio between components such as CD and DVD players, television sets, audio amplifiers, and mixing consoles. Line level sits between other levels of audio signal ...

. The second amplifier is typically a power amplifier (power amp). The preamplifier provides

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge t ...

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

s. For these systems some common sensors are

s, instrument pickups, and phonographs. Preamplifiers are often integrated into the audio inputs on

mixing console A mixing console or mixing desk is an electronic device for mixing audio signals, used in sound recording and reproduction and sound reinforcement systems. Inputs to the console include microphones, signals from electric or electronic inst ...

s, DJ mixers, and

sound card A sound card (also known as an audio card) is an internal expansion card that provides input and output of audio signals to and from a computer under the control of computer programs. The term ''sound card'' is also applied to external au ...

s. They can also be stand-alone devices

Examples

* The integrated preamplifier in a foil electret microphone. * The first stages of an

instrument amplifier An instrument amplifier is an electronic device that converts the often barely audible or purely electronic signal of a musical instrument into a larger electronic signal to feed to a loudspeaker. An instrument amplifier is used with musical ins ...

, 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 A concert is a live music performance in front of an audience. The performance may be by a single musician, sometimes then called a recital, or by a musical ensemble, such as an orchestra, choir, or band. Concerts are held in a wide variety ...

and

recording studio A recording studio is a specialized facility for sound recording, mixing, and audio production of instrumental or vocal musical performances, spoken words, and other sounds. They range in size from a small in-home project studio large en ...

applications. * As part of a stand-alone channel strip or channel strip built into an audio mixing desk. * A

masthead Masthead may refer to: * Nameplate (publishing), the banner name on the front page of a newspaper or periodical (UK "masthead") * Masthead (American publishing), details of the owners, publisher, departments, officers, contributors and address d ...

amplifier used with

television Television, sometimes shortened to TV, is a telecommunication Media (communication), medium for transmitting moving images and sound. The term can refer to a television set, or the medium of Transmission (telecommunications), television tra ...

receiver antenna or a

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioiso ...

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 A switched capacitor (SC) is an electronic circuit that implements a function by moving charges into and out of capacitors when electronic switches are opened and closed. Usually, non-overlapping clock signals are used to control the switches, so ...

circuit used to null the effects of mismatch offset in most CMOS comparator-based flash

analog-to-digital converter In electronics, an analog-to-digital converter (ADC, A/D, or A-to-D) is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a digital signal. An ADC may also provide ...

s * Due to its unique coloration, some preamplifiers can be emulated in software to be used in mixing.

External links

* {{music technology Electronic amplifiers Audio engineering

Description

Audio systems

Examples

See also

External links