Instrument amplifier
Encyclopedia
An instrument amplifier is an electronic amplifier
that converts the often barely audible or purely electronic signal from musical instruments such as an electric guitar
, an electric bass
, or an electric keyboard
into an electronic signal capable of driving a loudspeaker
that can be heard by the performers and audience. Combination ("combo") amplifiers include a preamplifier, a power amplifier, tone controls, and one or more speakers in a cabinet, a housing usually made of hardwood, plywood, particleboard, or, less commonly, moulded plastic. Instrument amplifiers for some instruments are also available without an internal speaker; these amplifiers have to be plugged into an external speaker cabinet.
Instrument amplifiers are available for specific instruments, including the electric guitar, electric bass, electric keyboards, and acoustic instruments such as the mandolin and banjo. Some amplifiers are designed for specific styles of music, such as the "traditional"-style "tweed" guitar amplifiers used by blues and country musicians, and the Marshall amplifiers used by hard rock and heavy metal bands.
Unlike home "hi-fi" amplifiers
or public address systems, which are designed to reproduce accurately the source sound signals with as little harmonic distortion as possible, instrument amplifiers are often designed to add additional tonal coloration to the original signal or emphasize (or de-emphasize) certain frequencies. The two exceptions are keyboard amplifiers and "acoustic" instrument amplifiers, which typically aim for a relatively flat frequency response.
Standard amplifiers, such as the Fender "tweed"-style amps and Gibson amps, are often used by traditional rock, blues, and country musicians who wish to create a "vintage" 1950s-style sound. They are used by electric guitarists, pedal steel guitar players, and blues harmonica
("harp") players. Combo amplifiers such as the Fender Super Reverb
have tube amplifiers, four 10" speakers, and built-in reverb
and "vibrato
" effects units.
These amps are designed to produce a variety of sounds ranging from a clean, warm sound (when used in country and soft rock) to a growling, natural overdrive, when the volume is set near its maximum, (when used for blues
, rockabilly
, and roots rock
). These amplifiers usually have a sharp treble roll-off
at 5 kHz to reduce the extreme high frequencies, and a bass roll-off at 60–100 Hz to reduce boominess. The nickname "tweed" refers to the lacquered beige-light brown fabric covering used on these amplifiers.
The smallest "combo" amplifiers, which are mainly used for rehearsal and warm-up purposes, may have only a single 8" or 10" speaker. Some harmonica players use these small combo amplifiers for concert performances, though, because it is easier to create natural overdrive with these lower-powered amplifiers. Larger combo amplifiers, with one 12 inch speaker or two or four 10 or 12 inch speakers are used for club performances. For large concert venues, performers may also use an amplifier "head" with several separate speaker cabinets (which usually contain two or four 12" speakers).
Amplifiers of this type, such as Marshall amplifiers, are used in a range of the louder, heavier genres of rock, including hard rock, heavy metal
, and hardcore punk
. This type of amplifier is available in a range of formats, ranging from smaller combo amplifiers for rehearsal and warm-up purposes to heavy "heads" which are designed to be used with separate speaker cabinets, which is colloquially referred to as a "stack."
In the late 1960s and early 1970s, public address systems at rock concerts were used mainly for the vocals. As a result, to get a loud electric guitar sound, early heavy metal
and rock-blues bands often used "stacks" of 4x12" Marshall speaker cabinets on the stage. In 1969 Jimi Hendrix
used four stacks to create a powerful lead sound, and in the early 1970s by the band Blue Öyster Cult
used an entire wall of Marshall Amplifiers to create a roaring wall of sound. In the 1980s, metal bands such as Slayer
and Yngwie Malmsteen also used "walls" of over 20 Marshall cabinets. However, by the 1980s and 1990s, most of the sound at live concerts was produced by the sound reinforcement system
rather than the onstage guitar amplifiers, so most of these cabinets were not connected to an amplifier. Instead, walls of speaker cabinets were used for aesthetic reasons.
Amplifiers for harder, heavier genres often use valve amplifiers (known as "tube amplifiers" in North America) also. Valve amplifiers have a "warmer" tone than those of transistor amps, particularly when overdriven. Instead of abruptly clipping off the signal at cut-off and saturation levels, the signal is rounded off more smoothly. Vacuum tubes also exhibit different harmonic effects than transistors. In contrast to the "tweed"-style amplifiers, which use speakers in an open-backed cabinet, companies such as Marshall tend to use 12" speakers in a closed-back cabinet. These amplifiers usually allow users to switch between "clean" and distorted tones (or a rhythm guitar
-style "crunch" tone and a sustained "lead"
tone) with a foot-operated switch.
are designed for bass guitar
s or more rarely, for upright bass
. They differ from amplifiers for the regular electric guitar in several respects. They have extended bass response and tone controls optimised for bass instruments, which produce pitches of 40 Hz, in the case of a standard four-string electric bass, or even lower for five- or six-string electric basses.
Higher-end bass amplifiers sometimes include compressor or limiter features, which help to keep the amplifier from distorting at high volume levels, and an XLR DI output for patching the bass signal directly into a mixing board or PA systems. Larger, more powerful bass amplifiers (300 or more watts) are often provided with external metal heat sinks or fans to help keep the amplifier cool.
Speaker cabinets designed for bass instrument amplification usually use larger loudspeakers (or more loudspeakers, in the case of the popular 4 X 10" cabinets, which contain four 10" speakers) than the cabinets used for other instruments, so that they can move the larger amounts of air needed to reproduce low frequencies. While the largest speakers commonly used for regular electric guitar are 12" speakers, electric bass speaker cabinets often use 15" speakers. Bass players who play styles of music that require an extended low-range response, such as death metal
, sometimes use speaker cabinets with 18" speakers.
The speakers used for bass instrument amplification tend to be more heavy-duty than speakers used for regular electric guitar, and the speaker cabinets are typically more rigidly constructed and heavily braced, to prevent unwanted buzzes and rattles. Bass cabinets often include bass reflex
ports or openings in the cabinet, which improve the bass response, especially at high volumes.
s, Hammond organ-style keyboards
, stage piano
s and electric piano
s. Since keyboard instruments contain a wide frequency range, from very low bass notes to extremely high pitches, keyboard amplifiers are often provided with a large woofer
speaker to handle the low notes and a horn (or tweeter) for the high notes.
Keyboard amplifiers intended for general use for a range of keyboard applications usually have very low distortion and extended, flat frequency response in both directions. The exception to this rule is keyboard amplifiers designed for the Hammond organ, such as the vintage Leslie speaker cabinet and modern recreations, which have a tube amplifier which is often turned up to add a warm, "growling" overdrive to the organ sound.
Unlike bass amplifiers and electric guitar amplifiers, keyboard amplifers are rarely used in the "amplifier head" and separate speaker cabinets configuration. Instead, most keyboard amplifiers are "combo" amplifiers that integrate the amplifier, tone controls, and speaker into a single wooden cabinet. Another unusual aspect of keyboard amplifiers is that they are often designed with a "wedge" shape, as used with monitor speakers. This allows the cabinet to be rocked back so that it will project sound upwards at a roughly 45' angle, which is more suitable for a seated keyboardist.
Keyboard amplifiers often have a simple onboard mixer with multiple inputs, so that keyboardists can control the tone and level of several keyboards. In some genres, such as progressive rock
, for example, keyboardists may perform with several synthesizers, electric pianos, and electro-mechanical keyboards.
and bluegrass
. They are similar in many ways to keyboard amplifiers, in that they have a relatively flat frequency response, and they are usually designed so that neither the power amplifier nor the speakers will introduce additional coloration.
To produce this relatively "clean" sound, these amplifiers often have very powerful amplifiers (providing up to 800 watts RMS), to provide additional "headroom" and prevent unwanted distortion. Since an 800 watt amplifier built with standard Class AB technology would be very heavy, some acoustic amplifier manufacturers use lightweight Class D amplifiers, which are also called "switching amplifiers."
Acoustic amplifiers are designed to produce a "clean", transparent, "acoustic" sound when used with acoustic instruments with built-in transducer pickups and/or microphones. The amplifiers often come with a simple mixer, so that the signals from a pickup and microphone can be blended. Since the early 2000s, it has become increasingly common for acoustic amplifiers to be provided with a range of digital effects, such as reverb and compression
. As well, these amplifiers often contain feedback
-suppressing devices, such as notch filters or parametric equalizers.
amplifiers used for radios and home stereo systems. Hi-fi home stereo amplifiers are designed to accurately reproduce the source sound signals from pre-recorded music, with as little harmonic distortion as possible. In contrast, instrument amplifiers are often designed to add additional tonal coloration to the original signal or emphasize certain frequencies. For electric instruments such as electric guitar, the amplifier helps to create the instrument's tone by boosting the input signal gain and distorting the signal, and by emphasizing frequencies deemed to be desirable (e.g., low frequencies) and de-emphasizing frequencies deemed to be undesirable (e.g., very high frequencies).
The two exceptions are keyboard amplifiers and acoustic amplifiers which are used by folk
and bluegrass music
ians for amplifying acoustic instruments such as acoustic guitar, violin, and mandolin
. Acoustic amplifiers typically aim for a relatively flat response across the entire frequency range, much like a Public Address system.
amplifier, which was often used with eight 10" speakers.
However, over subsequent decades, PA systems were substantially improved, and different approaches such as horn-loaded "bass bins" (in the 1980s) and subwoofers (1990s and 2000s) were used to amplify bass frequencies. As well, in the 1980s and 1990s, monitor systems were substantially improved, which allowed sound engineers to provide onstage musicians with a loud, clear, and full-range reproduction of their instruments' sound.
As a result of the improvements to PA systems and monitor systems, musicians in the 2000s no longer need to have huge, powerful amplifier systems; a small combo amplifier patched into the PA will suffice. In the 2000s, virtually all of the sound reaching the audience in large venues comes from the PA system. As well, in the 2000s onstage instrument amplifiers are more likely to be kept at a low volume, because high volume levels onstage makes it harder to control the sound mix and produce a clean sound.
As a result, in many large venues much of the onstage sound reaching the musicians now comes from the monitor speakers, not from the instrument amplifiers. While stacks of huge speaker cabinets and amplifiers are still used in concerts (especially in heavy metal), this is often mainly for aesthetics or to create a more authentic tone. The switch to smaller instrument amplifiers makes it easier for musicians to transport their equipment to performances. As well, it makes concert stage management easier at large clubs and festivals where several bands are performing in sequence, because the bands can be moved on and off the stage more quickly.
(transistor) technology.
Although tube amplifiers produce more heat than solid state amplifiers, few manufacturers of these units include cooling fans in the chassis. While tube amplifiers do need to attain a proper operating temperature
, if the temperature goes above this operating temperature, it may shorten the tubes' lifespan and lead to tonal inconsistencies.
and digital modeling technology to simulate many different combinations of amp and cabinets.
The output transistors of solid-state amplifiers can be passively cooled by using metal fins called heatsinks to radiate away the heat. For high-wattage amplifiers (over 800 watts), a fan is often used to move air across internal heatsinks.
Electronic amplifier
An electronic amplifier is a device for increasing the power of a signal.It does this by taking energy from a power supply and controlling the output to match the input signal shape but with a larger amplitude...
that converts the often barely audible or purely electronic signal from musical instruments such as an electric guitar
Electric guitar
An electric guitar is a guitar that uses the principle of direct electromagnetic induction to convert vibrations of its metal strings into electric audio signals. The signal generated by an electric guitar is too weak to drive a loudspeaker, so it is amplified before sending it to a loudspeaker...
, an electric bass
Bass guitar
The bass guitar is a stringed instrument played primarily with the fingers or thumb , or by using a pick....
, or an electric keyboard
Hammond organ
The Hammond organ is an electric organ invented by Laurens Hammond in 1934 and manufactured by the Hammond Organ Company. While the Hammond organ was originally sold to churches as a lower-cost alternative to the wind-driven pipe organ, in the 1960s and 1970s it became a standard keyboard...
into an electronic signal capable of driving a loudspeaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
that can be heard by the performers and audience. Combination ("combo") amplifiers include a preamplifier, a power amplifier, tone controls, and one or more speakers in a cabinet, a housing usually made of hardwood, plywood, particleboard, or, less commonly, moulded plastic. Instrument amplifiers for some instruments are also available without an internal speaker; these amplifiers have to be plugged into an external speaker cabinet.
Unlike home "hi-fi" amplifiers
AV receiver
AV receivers or audio-video receivers are one of the many consumer electronics components typically found within a home theatre system. Their primary purpose is to amplify sound from a multitude of possible audio sources as well as route video signals to your TV from various sources. The user may...
or public address systems, which are designed to reproduce accurately the source sound signals with as little harmonic distortion as possible, instrument amplifiers are often designed to add additional tonal coloration to the original signal or emphasize (or de-emphasize) certain frequencies. The two exceptions are keyboard amplifiers and "acoustic" instrument amplifiers, which typically aim for a relatively flat frequency response.
Standard amps
Harmonica
The harmonica, also called harp, French harp, blues harp, and mouth organ, is a free reed wind instrument used primarily in blues and American folk music, jazz, country, and rock and roll. It is played by blowing air into it or drawing air out by placing lips over individual holes or multiple holes...
("harp") players. Combo amplifiers such as the Fender Super Reverb
Fender Super Reverb
The Fender Super Reverb was a guitar amplifier made by Fender. It was introduced in 1963 and was discontinued in 1982. This was essentially a Fender Super amplifier with built-in reverb and vibrato. The original Super Reverb amplifiers were all tube design and featured spring reverb. There were...
have tube amplifiers, four 10" speakers, and built-in reverb
Reverberation
Reverberation is the persistence of sound in a particular space after the original sound is removed. A reverberation, or reverb, is created when a sound is produced in an enclosed space causing a large number of echoes to build up and then slowly decay as the sound is absorbed by the walls and air...
and "vibrato
Vibrato unit
A vibrato unit is an effects unit used to add tremolo to the sound of an electric instrument, most often an electric guitar. Vibrato units may be individual stomp boxes or built in to multi-effects units, but are traditionally built in to guitar amplifiers....
" effects units.
These amps are designed to produce a variety of sounds ranging from a clean, warm sound (when used in country and soft rock) to a growling, natural overdrive, when the volume is set near its maximum, (when used for blues
Blues
Blues is the name given to both a musical form and a music genre that originated in African-American communities of primarily the "Deep South" of the United States at the end of the 19th century from spirituals, work songs, field hollers, shouts and chants, and rhymed simple narrative ballads...
, rockabilly
Rockabilly
Rockabilly is one of the earliest styles of rock and roll music, dating to the early 1950s.The term rockabilly is a portmanteau of rock and hillbilly, the latter a reference to the country music that contributed strongly to the style's development...
, and roots rock
Roots rock
Roots rock is a term now used to describe rock music that looks back to rock's origins in folk, blues and country music. It is particularly associated with the creation of hybrid sub-genres from the later 1960s including country rock and Southern rock, which have been seen as responses to the...
). These amplifiers usually have a sharp treble roll-off
Roll-off
Roll-off is a term commonly used to describe the steepness of a transmission function with frequency, particularly in electrical network analysis, and most especially in connection with filter circuits in the transition between a passband and a stopband...
at 5 kHz to reduce the extreme high frequencies, and a bass roll-off at 60–100 Hz to reduce boominess. The nickname "tweed" refers to the lacquered beige-light brown fabric covering used on these amplifiers.
Hard rock and heavy metal
These electric guitar amplifiers add an aggressive "drive", intensity, and "edge" to the guitar sound with distortion effects, preamplification boost controls, and tone filters. While many of the most expensive, high-end models use tube amplifiers, there are also many models that use transistor amplifiers, or a mixture of the two technologies (i.e., a tube preamplifier with a transistor power amplifier).Heavy metal music
Heavy metal is a genre of rock music that developed in the late 1960s and early 1970s, largely in the Midlands of the United Kingdom and the United States...
, and hardcore punk
Hardcore punk
Hardcore punk is an underground music genre that originated in the late 1970s, following the mainstream success of punk rock. Hardcore is generally faster, thicker, and heavier than earlier punk rock. The origin of the term "hardcore punk" is uncertain. The Vancouver-based band D.O.A...
. This type of amplifier is available in a range of formats, ranging from smaller combo amplifiers for rehearsal and warm-up purposes to heavy "heads" which are designed to be used with separate speaker cabinets, which is colloquially referred to as a "stack."
In the late 1960s and early 1970s, public address systems at rock concerts were used mainly for the vocals. As a result, to get a loud electric guitar sound, early heavy metal
Heavy metal music
Heavy metal is a genre of rock music that developed in the late 1960s and early 1970s, largely in the Midlands of the United Kingdom and the United States...
and rock-blues bands often used "stacks" of 4x12" Marshall speaker cabinets on the stage. In 1969 Jimi Hendrix
Jimi Hendrix
James Marshall "Jimi" Hendrix was an American guitarist and singer-songwriter...
used four stacks to create a powerful lead sound, and in the early 1970s by the band Blue Öyster Cult
Blue Öyster Cult
Blue Öyster Cult, often abbreviated BÖC, is an American rock band, most of whose members first came together in Long Island, NY in 1967 as the band Soft White Underbelly...
used an entire wall of Marshall Amplifiers to create a roaring wall of sound. In the 1980s, metal bands such as Slayer
Slayer
Slayer is an American thrash metal band formed in Huntington Park, California, in 1981 by guitarists Jeff Hanneman and Kerry King. Slayer rose to fame with their 1986 release, Reign in Blood, and is credited as one of the "Big Four" thrash metal acts, along with Metallica, Megadeth and...
and Yngwie Malmsteen also used "walls" of over 20 Marshall cabinets. However, by the 1980s and 1990s, most of the sound at live concerts was produced by the sound reinforcement system
Sound reinforcement system
A sound reinforcement system is the combination of microphones, signal processors, amplifiers, and loudspeakers that makes live or pre-recorded sounds louder and may also distribute those sounds to a larger or more distant audience...
rather than the onstage guitar amplifiers, so most of these cabinets were not connected to an amplifier. Instead, walls of speaker cabinets were used for aesthetic reasons.
Rhythm guitar
Rhythm guitar is a technique and rôle that performs a combination of two functions: to provide all or part of the rhythmic pulse in conjunction with singers or other instruments; and to provide all or part of the harmony, ie. the chords, where a chord is a group of notes played together...
-style "crunch" tone and a sustained "lead"
Lead guitar
Lead guitar is a guitar part which plays melody lines, instrumental fill passages, guitar solos, and occasionally, some riffs within a song structure...
tone) with a foot-operated switch.
Bass
Bass amplifiersBass instrument amplification
Bass instrument amplification, used for the bass guitar, double bass and similar instruments, is distinct from other types of amplification systems due to the particular challenges associated with low-frequency sound reproduction. This distinction affects the design of the loudspeakers, the speaker...
are designed for bass guitar
Bass guitar
The bass guitar is a stringed instrument played primarily with the fingers or thumb , or by using a pick....
s or more rarely, for upright bass
Double bass
The double bass, also called the string bass, upright bass, standup bass or contrabass, is the largest and lowest-pitched bowed string instrument in the modern symphony orchestra, with strings usually tuned to E1, A1, D2 and G2...
. They differ from amplifiers for the regular electric guitar in several respects. They have extended bass response and tone controls optimised for bass instruments, which produce pitches of 40 Hz, in the case of a standard four-string electric bass, or even lower for five- or six-string electric basses.
Higher-end bass amplifiers sometimes include compressor or limiter features, which help to keep the amplifier from distorting at high volume levels, and an XLR DI output for patching the bass signal directly into a mixing board or PA systems. Larger, more powerful bass amplifiers (300 or more watts) are often provided with external metal heat sinks or fans to help keep the amplifier cool.
Death metal
Death metal is an extreme subgenre of heavy metal. It typically employs heavily distorted guitars, tremolo picking, deep growling vocals, blast beat drumming, minor keys or atonality, and complex song structures with multiple tempo changes....
, sometimes use speaker cabinets with 18" speakers.
The speakers used for bass instrument amplification tend to be more heavy-duty than speakers used for regular electric guitar, and the speaker cabinets are typically more rigidly constructed and heavily braced, to prevent unwanted buzzes and rattles. Bass cabinets often include bass reflex
Bass reflex
A Bass reflex system is a type of loudspeaker enclosure that uses the sound from the rear side of the diaphragm to increase the efficiency of the system at low frequencies as compared to a typical closed box loudspeaker or an infinite baffle mounting.A reflex port is the distinctive feature of a...
ports or openings in the cabinet, which improve the bass response, especially at high volumes.
Keyboard
This type of amplifier is used to amplify a range of electric and electronic keyboards, such as synthesizerSynthesizer
A synthesizer is an electronic instrument capable of producing sounds by generating electrical signals of different frequencies. These electrical signals are played through a loudspeaker or set of headphones...
s, Hammond organ-style keyboards
Hammond organ
The Hammond organ is an electric organ invented by Laurens Hammond in 1934 and manufactured by the Hammond Organ Company. While the Hammond organ was originally sold to churches as a lower-cost alternative to the wind-driven pipe organ, in the 1960s and 1970s it became a standard keyboard...
, stage piano
Stage piano
A stage piano is an electronic keyboard designed for use in live onstage performances by professional musicians. While stage pianos share some of the same features as digital pianos designed for in-home use and electronic synthesizers, they have a number of features which set them apart...
s and electric piano
Electric piano
An electric piano is an electric musical instrument.Electric pianos produce sounds mechanically and the sounds are turned into electrical signals by pickups. Unlike a synthesizer, the electric piano is not an electronic instrument, but electro-mechanical. The earliest electric pianos were invented...
s. Since keyboard instruments contain a wide frequency range, from very low bass notes to extremely high pitches, keyboard amplifiers are often provided with a large woofer
Woofer
Woofer is the term commonly used for a loudspeaker driver designed to produce low frequency sounds, typically from around 40 hertz up to about a kilohertz or higher. The name is from the onomatopoeic English word for a dog's bark, "woof"...
speaker to handle the low notes and a horn (or tweeter) for the high notes.
Keyboard amplifiers intended for general use for a range of keyboard applications usually have very low distortion and extended, flat frequency response in both directions. The exception to this rule is keyboard amplifiers designed for the Hammond organ, such as the vintage Leslie speaker cabinet and modern recreations, which have a tube amplifier which is often turned up to add a warm, "growling" overdrive to the organ sound.
Unlike bass amplifiers and electric guitar amplifiers, keyboard amplifers are rarely used in the "amplifier head" and separate speaker cabinets configuration. Instead, most keyboard amplifiers are "combo" amplifiers that integrate the amplifier, tone controls, and speaker into a single wooden cabinet. Another unusual aspect of keyboard amplifiers is that they are often designed with a "wedge" shape, as used with monitor speakers. This allows the cabinet to be rocked back so that it will project sound upwards at a roughly 45' angle, which is more suitable for a seated keyboardist.
Keyboard amplifiers often have a simple onboard mixer with multiple inputs, so that keyboardists can control the tone and level of several keyboards. In some genres, such as progressive rock
Progressive rock
Progressive rock is a subgenre of rock music that developed in the late 1960s and early 1970s as part of a "mostly British attempt to elevate rock music to new levels of artistic credibility." John Covach, in Contemporary Music Review, says that many thought it would not just "succeed the pop of...
, for example, keyboardists may perform with several synthesizers, electric pianos, and electro-mechanical keyboards.
Acoustic
These amplifiers are designed to be used with acoustic instruments such as violin ("fiddle"), mandolin, and acoustic guitar, especially for the way these instruments are used in relatively quiet genres such as folkFolk music
Folk music is an English term encompassing both traditional folk music and contemporary folk music. The term originated in the 19th century. Traditional folk music has been defined in several ways: as music transmitted by mouth, as music of the lower classes, and as music with unknown composers....
and bluegrass
Bluegrass music
Bluegrass music is a form of American roots music, and a sub-genre of country music. It has mixed roots in Scottish, English, Welsh and Irish traditional music...
. They are similar in many ways to keyboard amplifiers, in that they have a relatively flat frequency response, and they are usually designed so that neither the power amplifier nor the speakers will introduce additional coloration.
To produce this relatively "clean" sound, these amplifiers often have very powerful amplifiers (providing up to 800 watts RMS), to provide additional "headroom" and prevent unwanted distortion. Since an 800 watt amplifier built with standard Class AB technology would be very heavy, some acoustic amplifier manufacturers use lightweight Class D amplifiers, which are also called "switching amplifiers."
Acoustic amplifiers are designed to produce a "clean", transparent, "acoustic" sound when used with acoustic instruments with built-in transducer pickups and/or microphones. The amplifiers often come with a simple mixer, so that the signals from a pickup and microphone can be blended. Since the early 2000s, it has become increasingly common for acoustic amplifiers to be provided with a range of digital effects, such as reverb and compression
Gain compression
Gain compression is a reduction in 'differential' or 'slope' gain caused by nonlinearity of the transfer function of the amplifying device. This nonlinearity may be caused by heat due to power dissipation, or by overdriving the active device beyond its linear region...
. As well, these amplifiers often contain feedback
Feedback
Feedback describes the situation when output from an event or phenomenon in the past will influence an occurrence or occurrences of the same Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence an occurrence or...
-suppressing devices, such as notch filters or parametric equalizers.
Roles
Instrument amplifiers are designed for a different purpose than 'Hi-Fi' (high fidelity) stereoSTEREO
STEREO is a solar observation mission. Two nearly identical spacecraft were launched into orbits that cause them to respectively pull farther ahead of and fall gradually behind the Earth...
amplifiers used for radios and home stereo systems. Hi-fi home stereo amplifiers are designed to accurately reproduce the source sound signals from pre-recorded music, with as little harmonic distortion as possible. In contrast, instrument amplifiers are often designed to add additional tonal coloration to the original signal or emphasize certain frequencies. For electric instruments such as electric guitar, the amplifier helps to create the instrument's tone by boosting the input signal gain and distorting the signal, and by emphasizing frequencies deemed to be desirable (e.g., low frequencies) and de-emphasizing frequencies deemed to be undesirable (e.g., very high frequencies).
The two exceptions are keyboard amplifiers and acoustic amplifiers which are used by folk
Folk music
Folk music is an English term encompassing both traditional folk music and contemporary folk music. The term originated in the 19th century. Traditional folk music has been defined in several ways: as music transmitted by mouth, as music of the lower classes, and as music with unknown composers....
and bluegrass music
Bluegrass music
Bluegrass music is a form of American roots music, and a sub-genre of country music. It has mixed roots in Scottish, English, Welsh and Irish traditional music...
ians for amplifying acoustic instruments such as acoustic guitar, violin, and mandolin
Mandolin
A mandolin is a musical instrument in the lute family . It descends from the mandore, a soprano member of the lute family. The mandolin soundboard comes in many shapes—but generally round or teardrop-shaped, sometimes with scrolls or other projections. A mandolin may have f-holes, or a single...
. Acoustic amplifiers typically aim for a relatively flat response across the entire frequency range, much like a Public Address system.
Size and power rating
In the 1960s and 1970s, large, heavy, high output power amplifiers were preferred for instrument amplifiers, especially for large concerts, because public address systems were generally only used to amplify the vocals. Moreover, in the 1960s, PA systems typically did not use monitor speaker systems to amplify the music for the onstage musicians. Instead, the musicians were expected to have instrument amplifiers that were powerful enough to provide amplification for the stage and audience. In late 1960s and early 1970s rock concerts, bands often used large stacks of speaker cabinets powered by heavy tube amplifiers such as the Super Valve Technology (SVT)Ampeg SVT
The Ampeg SVT is a bass amplifier made by Ampeg. The SVT, which stands for "Super Valve Technology", was designed by Bill Hughes and introduced in 1969. The SVT bass head produced 300 watts at a time when most amplifiers made less than 100. The SVT has been through many design changes over the...
amplifier, which was often used with eight 10" speakers.
However, over subsequent decades, PA systems were substantially improved, and different approaches such as horn-loaded "bass bins" (in the 1980s) and subwoofers (1990s and 2000s) were used to amplify bass frequencies. As well, in the 1980s and 1990s, monitor systems were substantially improved, which allowed sound engineers to provide onstage musicians with a loud, clear, and full-range reproduction of their instruments' sound.
As a result of the improvements to PA systems and monitor systems, musicians in the 2000s no longer need to have huge, powerful amplifier systems; a small combo amplifier patched into the PA will suffice. In the 2000s, virtually all of the sound reaching the audience in large venues comes from the PA system. As well, in the 2000s onstage instrument amplifiers are more likely to be kept at a low volume, because high volume levels onstage makes it harder to control the sound mix and produce a clean sound.
As a result, in many large venues much of the onstage sound reaching the musicians now comes from the monitor speakers, not from the instrument amplifiers. While stacks of huge speaker cabinets and amplifiers are still used in concerts (especially in heavy metal), this is often mainly for aesthetics or to create a more authentic tone. The switch to smaller instrument amplifiers makes it easier for musicians to transport their equipment to performances. As well, it makes concert stage management easier at large clubs and festivals where several bands are performing in sequence, because the bands can be moved on and off the stage more quickly.
Amplifier technology
Instrument amplifiers may be based on thermionic ("tube" or "valve") or solid stateSolid state (electronics)
Solid-state electronics are those circuits or devices built entirely from solid materials and in which the electrons, or other charge carriers, are confined entirely within the solid material...
(transistor) technology.
Tube Amplifiers
Vacuum tubes were the dominant active electronic components in amplifiers manufactured from the 1930s through the early 1970s, and tube amplifiers continue to be preferred by some professional musicians. Some musicians believe that tube amplifiers produce a "warmer" or more "natural" sound than solid state units. However, these subjective assessments of the attributes of tube amplifiers' sound qualities are the subject of ongoing debate.Although tube amplifiers produce more heat than solid state amplifiers, few manufacturers of these units include cooling fans in the chassis. While tube amplifiers do need to attain a proper operating temperature
Operating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...
, if the temperature goes above this operating temperature, it may shorten the tubes' lifespan and lead to tonal inconsistencies.
Solid-state Amplifiers
By the 1960s and 1970s, semiconductor transistor-based amplifiers began to become more popular because they are less expensive, lighter-weight, and require less maintenance. In some cases, tube and solid-state technologies are used together in amplifiers. A common setup is the use of a tube preamplifier with a solid-state power amplifier. There are also an increasing range of products that use digital signal processingDigital signal processing
Digital signal processing is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing...
and digital modeling technology to simulate many different combinations of amp and cabinets.
The output transistors of solid-state amplifiers can be passively cooled by using metal fins called heatsinks to radiate away the heat. For high-wattage amplifiers (over 800 watts), a fan is often used to move air across internal heatsinks.
See also
- AmplifierAmplifierGenerally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
- Electronic amplifierElectronic amplifierAn electronic amplifier is a device for increasing the power of a signal.It does this by taking energy from a power supply and controlling the output to match the input signal shape but with a larger amplitude...
- Guitar amplifierGuitar amplifierA guitar amplifier is an electronic amplifier designed to make the signal of an electric or acoustic guitar louder so that it will produce sound through a loudspeaker...
- Guitar speakerGuitar speakerA guitar speaker is a loudspeaker – specifically the driver part – designed for use in or with the guitar amplifier of an electric guitar...
- Guitar speaker cabinet
- Isolation cabinet (guitar)Isolation cabinet (guitar)The characteristic sound of a tube guitar amplifier as heard on the majority of professional recordings is achieved by playing the amplifier at high volumes, and using one or more microphones to capture the sound. Turning the volume up causes the pre-amplifier to drive the power amplifier into...
- Valve sound
- Bass instrument amplificationBass instrument amplificationBass instrument amplification, used for the bass guitar, double bass and similar instruments, is distinct from other types of amplification systems due to the particular challenges associated with low-frequency sound reproduction. This distinction affects the design of the loudspeakers, the speaker...
- Effects unitEffects unitEffects units are electronic devices that alter how a musical instrument or other audio source sounds. Some effects subtly "color" a sound, while others transform it dramatically. Effects are used during live performances or in the studio, typically with electric guitar, keyboard and bass...
- Distortion (guitar)Distortion (guitar)Distortion effects create "warm", "dirty" and "fuzzy" sounds by compressing the peaks of a musical instrument's sound wave and adding overtones. The three principal types of distortion effects are overdrive, distortion and fuzz. Distortion effects are sometimes called “gain” effects, as distorted...
- Power attenuator (guitar)Power attenuator (guitar)In conjunction with an electric guitar amplifier, a power attenuator is used to divert and dissipate some or all of the amplifier's excess or unneeded power in order to reduce the volume of sound produced by the speaker.- Explanation :...
- Sound reinforcement systemSound reinforcement systemA sound reinforcement system is the combination of microphones, signal processors, amplifiers, and loudspeakers that makes live or pre-recorded sounds louder and may also distribute those sounds to a larger or more distant audience...
External links
- Duncan's amp pages - all sorts of information, especially, but not only, on valve guitar amplifiers
- List of books about guitar amplifiers and guitar amplifier tone
- Tons of Tones !! : Technical site for Guitar Amplifier Modelling on Digital Multi-effect units