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 (information theory), signal (a time-varying voltage or Electric current, current). It is a two-port network, two-port ...

that converts a weak

electrical signal A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology. In ...

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

power amplifier An audio power amplifier (or power amp) amplifies low-power electronic audio signals, such as the signal from a radio receiver or an electric guitar pickup, to a level that is high enough for driving loudspeakers or headphones. Audio power a ...

and a

loudspeaker A loudspeaker (commonly referred to as a speaker or, more fully, a speaker system) is a combination of one or more speaker drivers, an enclosure, and electrical connections (possibly including a crossover network). The speaker driver is an ...

. 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 publi ...

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

sensor A sensor is often defined as a device that receives and responds to a signal or stimulus. The stimulus is the quantity, property, or condition that is sensed and converted into electrical signal. In the broadest definition, a sensor is a devi ...

to reduce the effects of

noise Noise is sound, chiefly unwanted, unintentional, or harmful sound considered unpleasant, loud, or disruptive to mental or hearing faculties. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrat ...

and

interference Interference is the act of interfering, invading, or poaching. Interference may also refer to: Communications * Interference (communication), anything which alters, modifies, or disrupts a message * Adjacent-channel interference, caused by extra ...

Description

An ideal preamp will be linear (have a constant gain through its operating range) and have high

input impedance In electrical engineering, the input impedance of an electrical network is the measure of the opposition to current ( impedance), both static ( resistance) and dynamic ( reactance), into a load network or circuit that is ''external'' to the elec ...

(requiring only a minimal amount of current to sense the input signal) and low

output impedance In electrical engineering, the output impedance of an electrical network is the measure of the opposition to current flow ( impedance), both static ( resistance) and dynamic ( reactance), into the load network being connected that is ''internal ...

(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 noise power, often expressed in deci ...

(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 Noise figure (NF) and noise factor (''F'') are figures of merit that indicate degradation of the signal-to-noise ratio (SNR) that is caused by components in a signal chain. These figures of merit are used to evaluate the performance of an amplifie ...

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 Audio power, strength of an audio signal used to transmit analog (signal), analog sound between audio components such as compact disc, CD and Digital Versatile Disc, DVD players, television sets, audio amplifiers, and ...

. The second amplifier is typically a

(power amp). The preamplifier provides

voltage Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...

gain (e.g., from 10 mV to 1 V) but no significant

current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (hydr ...

gain. The power amplifier provides the higher current necessary to drive

s. For these systems, some common sensors are

s, instrument pickups, and

phonograph A phonograph, later called a gramophone, and since the 1940s a record player, or more recently a turntable, is a device for the mechanical and analogue reproduction of sound. The sound vibration Waveform, waveforms are recorded as correspond ...

s. Preamplifiers are often integrated into the audio inputs on

mixing console A mixing console or mixing desk is an electronic device for Audio mixing (recorded music), mixing audio signals, used in sound recording and reproduction and sound reinforcement systems. Inputs to the console include microphones, signals fro ...

DJ mixer A DJ mixer is a type of audio mixing console used by disc jockeys (DJs) to control and manipulate multiple audio signals. Some DJs use the mixer to make seamless transitions from one song to another when they are playing records at a dance club. ...

s, 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 audio ...

s. They can also be stand-alone devices.

Examples

* The integrated preamplifier in a foil

electret microphone An electret microphone is a microphone whose diaphragm forms a capacitor (historically-termed a ''condenser'') that incorporates an electret. The electret's permanent electric dipole provides a constant charge on the capacitor. Sound wave ...

* The first stage of an

instrument amplifier An instrument amplifier is an electronic amplifier 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 music ...

, 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 A concert, often known informally as a gig or show, is a live performance of music in front of an audience. The performance may be carried by a single musician, in which case it is sometimes called a recital, or by a musical ensemble such as an ...

and

recording studio A recording studio is a specialized facility for Sound recording and reproduction, recording and Audio mixing, mixing of instrumental or vocal musical performances, spoken words, and other sounds. They range in size from a small in-home proje ...

applications * Part of a stand-alone

channel strip A ''channel strip'' is a device that allows the output of an audio device to be amplified to a line level and integrated into some other system. An audio channel strip may be a stand-alone unit or one of many units built into a mixing desk. It ...

or channel strip built into an audio

mixing desk 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 instr ...

* A masthead amplifier used with

television Television (TV) is a telecommunication medium for transmitting moving images and sound. Additionally, the term can refer to a physical television set rather than the medium of transmission. Television is a mass medium for advertising, ...

receiver 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

satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...

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

photodiode A photodiode is a semiconductor diode sensitive to photon radiation, such as visible light, infrared or ultraviolet radiation, X-rays and gamma rays. It produces an electrical current when it absorbs photons. This can be used for detection and me ...

s * A

phono stage A phono stage, also known as a phono amplifier or phono preamplifier, is an electronic audio component that amplifies the signal from a turntable to a level that will allow it to be heard when connected to a sound system. A phono stage is needed to ...

amplifying the signal from a

cartridge to the ''line-level'' input of common power amplifiers * 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 ...

circuit used to null the effects of mismatch offset in most

CMOS Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss ", , ) is a type of MOSFET, metal–oxide–semiconductor field-effect transistor (MOSFET) semiconductor device fabrication, fabrication process that uses complementary an ...

comparator-based

flash analog-to-digital converter A flash ADC (also known as a direct-conversion ADC) is a type of analog-to-digital converter that uses a linear voltage ladder with a comparator at each "rung" of the ladder to compare the input voltage to successive reference voltages. Often thes ...

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

References

External links

* {{music technology Electronic amplifiers Audio engineering

Description

Audio systems

Examples

See also

References

External links