Guitar amplifier
Encyclopedia
A 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
. Most guitar amplifiers can also modify the instrument's tone by emphasizing or de-emphasizing certain frequencies and adding electronic effects.
Amplifiers consist of one or more circuit stages which have unique responsibilities in the modification of the input signal. The power amplifier
or output stage produces a high current signal to drive a speaker to produce sound. One or more preamplifier
stages precede the power amplifier stage. The preamplifier is a voltage amplifier that amplifies the guitar signal to a level that can drive the power stage. There may be one or more tone stages which affect the character of the guitar signal: before the preamp stage (as in the case of guitar pedals), in between the preamp and power stages (as in the cases of effects loop or many dedicated amplifier tone circuits), in between multiple stacked preamp stages, or in feedback loops from a post-preamp signal to an earlier pre-preamp signal (as in the case of presence modifier circuits). The tone stages may also have electronic effects such as equalization
, compression, distortion, chorus
, or reverb
. Amplifiers may use vacuum tubes (in Britain they are called valves), or solid-state (transistor) devices, or both.
There are two configurations of guitar amplifiers: combination ("combo") amplifiers, which include an amplifier and anywhere from one to four speakers in a wooden cabinet; and the standalone amplifier (often called a "head" or "amp head"), which does not include a speaker, but rather passes the signal to a speaker cabinet or "cab". Guitar amplifiers range in price and quality from small, low-powered practice amplifiers, designed for students, which sell for less than US$50, to expensive "boutique" amplifiers which are custom-made for professional musicians and can cost thousands of dollars.
s and rectifier
tubes
allowed the production of economical built-in power supplies
that could be plugged into wall sockets, instead of heavy multiple battery packs
, since rechargeable batteries wouldn't be lightweight until later on. While guitar amplifiers from the beginning were used to amplify acoustic guitar
, electronic amplification of guitar was first widely popularized by the 1930s and 1940s craze for Hawaiian music, which extensively employed the amplified lap steel Hawaiian guitar
.
Tone controls on early guitar amplifiers were very simple and provided a great deal of treble boost, but the limited controls, the loudspeakers used, and the low power of the amplifiers (typically 15 watts or less prior to the mid-1950s) gave poor high treble and bass output. Some models also provided effects
such as spring reverb
and/or an electronic tremolo
unit. Early Fender amps labeled tremolo as "vibrato" and labeled the vibrato arm of the Stratocaster guitar as a "tremolo bar" (see vibrato unit
, electric guitar
, and tremolo
).
In the 1960s, guitarists experimented with distortion
produced by deliberately overdriving their amplifiers. The Kinks
guitarist Dave Davies produced early distortion effects by connecting the already distorted output of one amplifier into the input of another. Later, most guitar amps were provided with preamplifier distortion controls, and "fuzz boxes" and other effects units were engineered to safely and reliably produce these sounds. In the 2000s overdrive and distortion has become an integral part of many styles of electric guitar playing, ranging from blues rock to heavy metal
and hardcore punk
.
Guitar amplifiers were at first used with bass guitars and electronic keyboard
s, but other instruments produce a wider frequency range and need a suitable amplifier and full-range speaker system. Much more amplifier power is required to reproduce low-frequency sound, especially at high volume. Reproducing low frequencies also requires a suitable woofer
or subwoofer
speaker and enclosure
. Woofer enclosures need to be larger and more sturdily built than cabinets for mid-range
or high-frequency (tweeter
) speakers.
Guitar amplifiers are manufactured in two main forms. The "combination" (or "combo") amplifier contains the amplifier head and guitar speaker
s in a single unit which is typically housed in a rectangular wooden box. The amplifier head or "amp head" contains the electronic circuitry constituting the preamp, built-in effects processing, and the power amplifier. Combo amps have at least one 1/4" input jack where the patch cord from the electric guitar can be plugged in. Other jacks may also be provided, such as an additional input jack, "send" and "return" jacks to create an effects loop (for connecting electronic effects such as compression, reverb, etc.), an extension speaker jack (for connecting an additional speaker cabinet). Some smaller practice amps have stereo RCA jacks for connecting a CD player, iPod
or other sound source and a 1/4" headphone jack so that the player can practice without disturbing neighbours or family members.
Some amplifiers have a line out jack for connecting the amplifier's signal to a PA system or recording console or to connect the amplifier to another guitar amp. In but most styles of rock and blues guitar, the line out is not used to connect the guitar amp to a PA system or recording console, because the tonal coloration and overdrive from the amplifier and speaker is considered an important part of the amplifier's sound. However, players do use the line out to connect one guitar amplifier to another amplifier, in order to create different tone colors or sound effects.
In the "amp head" form, the amplifier head is separate from the speakers, and joined to them by speaker cables. The separate amplifier is called an amplifier head, and is commonly placed on top of one or more loudspeaker enclosures. A separate amplifier head placed atop a guitar speaker enclosure or guitar speaker cabinet forms an amplifier "stack" or "amp stack". Amp heads may also have the different types of input and output jacks listed above in the combo section. In addition to a 1/4" input jack, acoustic guitar amplifiers typically have an additional input jack for a microphone
, which is easily identified because it will use a three-pin XLR connector
. Phantom power
is not often provided on general-use amps, restricting the choice of microphones for use with these inputs. However, for high-end acoustic amplifiers, phantom power is often provided, so that musicians can use condenser microphones.
Amplifiers used with electric guitars may be solid-state, which are lighter in weight and less expensive than tube amplifiers. Most guitarists, particularly in the genres of blues and rock, prefer the sound of vacuum tube
amplifiers despite their higher cost, heavier weight, the need to periodically replace tubes and need to re-bias the output tubes (every year or two with moderate use). Some companies design amplifiers that require no biasing as long as properly rated tubes are used. Some modern amplifiers use a mixture of tube and solid-state technologies.
Since the advent of microprocessor
s and digital signal processing, "modeling amps" have been developed in the late 1990s, these can simulate the sounds of a variety of well-known tube amplifiers without needing to use vacuum tubes. Amplifiers with processors and software emulate the sound of a classic amp well, but from the player's point of view the response of these amplifiers may not feel the same as the digital modeling does not accurately model all aspects of a tube amplifier.
A wide range of instrument amplifiers is available, some for general purposes and others designed for specific instruments or particular sounds. These include:
Vacuum tubes (valves) were by far the dominant active electronic components in most instrument amplifier applications until the 1970s, when semiconductors (transistors) started taking over for performance and economic reasons, including heat and weight reduction, and improved reliability. High-end tube instrument amplifiers have survived as one of few exceptions, because of the sound quality. Typically, one or more dual triode
s are used in the preamplifier section in order to provide sufficient voltage gain to offset losses by tone controls and to drive the power amplifier section.
The output tubes are often arranged in a class AB push-pull
connection to improve efficiency; this requires another triode or dual triode to split the phase
of the signal. The tubes of the power amplifier stage are almost always of the pentode
or beam tetrode
type (also known as "kinkless tetrodes", hence the KTxx nomenclature). Some high power models use paralleled pairs of output tubes (four or more in total) in push-pull. Except for the light negative feedback
from the secondary end of the output transformer to the driver stage, most amplifying stages work in "raw" open-loop mode. Some designs employ current feedback via unbypassed cathode resistors.
Since most tubes show "soft clipping" gain non-linearity, applying an input signal high enough to overdrive any stage tends to produce favorably natural distortion. Today, most vacuum tube amplifiers are based on the ECC83/12AX7
/7025 (dual triode) tubes for the preamplifier and driver sections and the EL84
/6BQ5 or EL34
/6CA7/KT77 or 6L6
/KT66 or 6V6
tubes for the power output section. Some use the KT88
/6550 beam power
tubes in the output stage. The differing codes for equivalent tubes generally reflect those used by the original European or U.S.A. based manufacturers. These tubes are now mainly manufactured in Russia, China and Eastern European countries. Some amplifiers, such as the Marshall Silver Jubilee, use solid-state components in the preamp, most commonly diodes, to create distortion, a design feature known as diode clipping.
Tube instrument amplifiers are often equipped with lower-grade transformers and simpler power regulation circuits than those of hi-fi amplifiers. They are usually not only for cost-saving reasons, but also are considered as a factor in sound creation . For example, a simple power regulation circuit's output tends to sag when there is a heavy load (that is, high output power) and vacuum tubes usually lose gain factors with lower power voltages. This results in a somewhat compressed sound which could be criticized as a "poor dynamic range" in case of hi-fi amplifiers, but could be desirable as "long sustain" of sounds on a guitar amplifier. Some tube guitar amplifiers use a rectifier
tube instead of solid-state diodes specifically for this reason.
Unfortunately, most amplifiers offer a fixed amount of sag, and this fixed amount can only be attained at full volumes. A small minority of amplifiers offer sag control via either multiple rectifiers or the Sag Circuit (a non-traditional power supply design patented by Maven Peal® Instruments). Amplifiers with multiple rectifiers can offer up to two sag settings (amounts), while the Sag Circuit provides a Sag control knob, which allows range of sag control at all volumes (by interacting with a wattage control knob).
Some models have a "spring reverb" unit that simulates the reverberation
of an echoic ambient. A reverb unit usually consists of one or more coil springs driven by the preamplifier section using a transducer driver similar to a loudspeaker at one end and an electro-magnetic pickup and preamplifier stage at the other end that picks up the long sustaining spring vibration, which is then mixed with the original signal. Some guitar amplifiers have a tremolo
control. An internal oscillator generates a low frequency continuous signal which can modulate the input signal's amplitude or the output tubes' bias, thereby producing a tremolo effect.
Tube amps have the following technical disadvantages in comparison to solid-state amps. They are bulky and heavy, primarily due to the iron in power and output transformer
s. Solid-state amplifiers still require power transformers, but are usually direct-coupled and don't need output transformers. Glass tubes are fragile, and require more care and consideration when equipment is moved repeatedly. Tube performance can deteriorate slightly over time before eventual catastrophic failure.
When tube vacuum is maintained at a high level, though, excellent performance and life is possible. They are prone to pick up mechanical noises (microphonic noise
), although such electro-mechanical feedback from the loudspeaker to the tubes in combo amplifiers may contribute to sound creation. Tubes benefit from a heater warm-up period before the application of high tension anode voltages; this allows the tube cathodes to operate without damage and so prolongs tube life. This is of particular importance for amplifiers with solid-state rectifiers.
Tube amps have the following technical advantages over solid-state amps. Compared to semiconductors, tubes have a very low "drift" (of specs) over a wide range of operating conditions, specifically high heat/high power. Semiconductors are very heat-sensitive by comparison and this fact usually leads to compromises in solid-state amplifier designs. When a tube fails, it is replaceable. While solid-state devices are also replaceable, it is usually a much more involved process (i.e., having the amplifier tested by a professional, removing the faulty component, and replacing it).
For working musicians this is usually a huge problem by comparison to looking in the back of a tube amp at the tubes and simply replacing the faulty tube. In addition, tubes can easily be removed and tested, while transistors cannot. Tube amplifiers respond differently from transistor amplifiers when signal levels approach and reach the point of clipping
. In a tube-powered amplifier, the transition from linear amplification to limiting is less abrupt than in a solid-state unit, resulting in a less grating form of distortion at the onset of clipping. For this reason, some guitarists prefer the sound of an all-tube amplifier; the aesthetic properties of tube versus solid-state amps, though, are a topic of debate in the guitarist community.
(solid-state) circuits, and some designs incorporate tubes in the preamp stage for their subjectively warmer overdrive sound. Tubes create warm overdrive sounds because instead of cutting the peaked signal off, they more or less pull the peaked audio information back (like natural compression) which creates a fuzzy overdrive sound. While this is a desirable attribute in many cases, the tube's characteristic will "color" all the sounds at any volume, unlike solid-state.
High-end solid-state amplifiers are less common, since many professional guitarists tend to favor vacuum tubes. Some jazz guitarists, however, tend to favor the "cleaner" sound of solid-state amplifiers, preferring not to color the sound of their guitar with the tube distortion and compression so popular with rock, blues, and metal musicians.. Solid-state amplifiers vary in output power, functionality, size, price, and sound quality in a wide range, from practice amplifiers to professional models. Some inexpensive amplifiers have only a single volume control and a one or two tone controls .
Amps, Fender Super Champ XD and the Roland Bolt amplifier, which is thereby classed as a 'hybrid' amp. Randall Amplifier's
current flagship models, the V2 and T2, use hybrid amp technology. Alternatively, a tube pre-amp can feed a solid-state output stage, as in models from Kustom
and Vox
. This approach dispenses with the need for an output transformer and allow modern power levels to be easily achieved.
to simulate the sound of well-known guitar amps, cabinets, and effects, as well as simulating the way traditional speaker cabinets sound when mixed with different types of microphones. They may also be an original creation not meant to simulate any particular real world guitar amp at all, instead allowing the user to create their own unique sound. Such as the original creations of companies like AcmeBarGig or Peavey
. This is usually achieved through digital processing. Modeling technology offers several advantages over traditional amplification. A modeling amp typically is capable of a wide range of tones and effects, and offers cabinet simulation, so it can be recorded without a microphone. Most modeling amps digitize the input signal and use a DSP
, a dedicated microprocessor, to process the signal with digital computation. Some modeling amps incorporate vacuum tubes, digital processing, and some form of power attenuation.
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.
In the case of electric guitars, an amplifier stack consisting of a head atop one cabinet is commonly called a half stack, while a head atop two cabinets is referred to as a full stack. The cabinet which the head sits on often has an angled top in front, while the lower cabinet of a full stack has a straight front. The first version of the Marshall stack was an amp head on an 8x12 cabinet, meaning a single speaker cabinet containing eight 12" guitar speakers. After six of these cabinets were made, the cabinet arrangement was changed to an amp head on two 4x12 cabinets, meaning four 12" speakers, to enable transporting the amp rig.
In heavy metal bands, the term "double stack" or "full stack" is sometimes used to refer to two stacks, with the main amplifier section of a second amplifier serving as a slave to the first and four speaker cabinets in total. Another name for the "Head & Cab" that comes from the 1960s and 1970s is "Piggyback". Vox amp stacks could be put on a tiltable frame with casters. Fender heads could be attached to the cab and had "Tilt-Back" legs, like those used on larger Fender combo amps. Typically, a guitar amp's preamplifier section (known as a 'pre') provides sufficient gain so that an instrument can be connected directly to its input, and its main amplification section (known as the 'power stage') sufficient power
to connect loudspeakers directly to its output
, both without requiring extra amplification.
Some touring bands have used the appearance of a large array of guitar amplifiers for aesthetic reasons. Some of these arrangements include one or more actual guitar cabinets, while others do not. In reference to a photograph (left) taken during an Immortal
gig, showing that what appeared to the audience to be a wide formation of equipment was actually only the fronts of amplifiers mounted on a large frame, Gizmodo
writer Rosa Golijan investigated the phenomenon and found that it was "not too uncommon".
Another arrangement, often used for public address
amplifier systems, is to provide two stages of amplification in separate units. First a preamplifier
or mixer is used to boost the instrument output, normally to line level
, and perhaps to mix signals from several instruments. The output
from this preamplifier is then connected to the input of a power amplifier, which powers the loudspeakers.
Performing musicians that use the "two-stage" approach (as opposed to an amplifier with an integrated preamplifier and power amplifier) often want to custom-design a combination of equipment that best suits their musical or technical needs, and gives them more tonal and technical options. Some musicians require preamps that include specific features. Acoustic performers sometimes require preamps with "notch" filters (to prevent feedback), reverb, an XLR DI output, or parametric equalization. Hard rock, metal, or punk performers may desire a preamplifier with a range of distortion effects. As well, some musicians have specific power amplifier requirements, such as low-noise design, very high wattage, the inclusion of limiter features to prevent distortion and speaker damage, or biamp-capable operation.
With the "two-stage" approach, the preamplifier and power amplifier are often mounted together in a rack case
. This case may be either free-standing or placed on top of a loudspeaker cabinet. If many rack-mounted effects are used, the rack may be a large unit on wheels. Some touring players need several racks of effects units to reproduce on stage the sounds they have produced in the studio. At the other extreme, if a small rack case containing both preamp and power amp is placed on top of a guitar speaker cabinet, the distinction between a rack and a traditional amp head begins to blur. Another variation is to combine the power amplifier into the speaker cabinet, an arrangement called a powered speaker, and use these with a separate preamp, sometimes combined into an effects pedal board or floor preamp/processor.
Preamplifiers are also used to connect very low-output or high-impedance
instruments to instrument amplifiers. When piezoelectric transducers are used on upright bass or other acoustic instruments, the signal coming directly from the transducer is often too weak and it does not have the correct impedance for direct connection to an instrument amplifier. Small, battery-powered preamps are often used with acoustic instruments to resolve these problems.
Power attenuation can be used with either low-power or high-power amplifiers, resulting in variable-power amplifiers. A high-power amplifier with power attenuation can produce power-tube distortion through a wide range of listening volumes. Speaker efficiency is also a major factor affecting a tube amplifier's maximum volume. For bass instruments, higher-power amplifiers are needed to reproduce low-frequency sounds. While an electric guitarist would be able to play at a small club with a 50-watt amplifier, a bass player performing in the same venue would probably need an amplifier with 200 or more watts.
is a feature available on many guitar amplifiers that is not typically found on keyboard or bass guitar amplifiers. Tube guitar amplifiers can produce distortion through pre-distortion equalization, preamp tube distortion, post-distortion EQ, power-tube distortion, tube rectifier compression, output transformer distortion, guitar speaker distortion, and guitar speaker and cabinet frequency response. Distortion sound or "texture" from guitar amplifiers is further shaped or processed through the frequency response and distortion factors in the microphones (their response, placement, and multi-microphone comb filtering effects), microphone preamps, mixer channel equalization, and compression. Additionally, the basic sound produced by the guitar amplifier can be changed and shaped by adding distortion and/or equalization effect pedals before the amp's input jack, in the effects loop just before the tube power amp, or after the power tubes.
in a separate cabinet. A soundproofed isolation cabinet
, isolation box, isolation booth, or isolation room can be used.
The simplest guitar amplifiers have only a volume control. Most have at least a gain control and a master volume control. The gain control is equivalent to the distortion control on a distortion pedal, and similarly may have a side-effect of changing the proportion of bass and treble sent to the next stage.
A simple amplifier's tone controls typically include passive bass and treble controls. In some cases, a midrange control is provided. The amplifier's master volume control restricts the amount of signal permitted through to the driver stage and the power amplifier. When using a power attenuator with a tube amplifier, the master volume no longer acts as the master volume control. Instead, the power attenuator's attenuation control controls the power delivered to the speaker, and the amplifier's master volume control determines the amount of power-tube distortion. Power-supply based power reduction is controlled by a knob on the tube power amp, variously labeled "Wattage", "Power", "Scale", "Power Scale", or "Power Dampening".
's Jon Lord
played his Hammond Organ
through a distorted Marshall
amp to create a sound more suitable for heavy rock. String instruments and vocals are also put through guitar amps to add distortion effects. Some blues harp
players also use guitar or bass amps to create a warmer overdrive sound for their harmonica playing; 1950s-style "tweed" amps are often used for this purpose, such as Fender Bassman combo amps.
Recording engineers occasionally run pre-recorded parts through miked guitar amps, a process called re-amping. When a guitar part is recorded "dry" (e.g., without effects or distortion), straight into the mixing board for a recording, this gives the producer and mixing engineer much more flexibility to create new re-mixes or new tones from the recording. If a guitar player records an electric guitar part that is run through a chorus pedal and a distortion pedal, there is little that can be done at the "mix-down" stage to change the sound of this recording, beyond "tweaking" the equalization and modifying the level. Since re-mixing or mixdown can take place weeks, months, or even years after the original recording session, it may be impossible to have the guitarist come in to re-record a new part.
If the dry guitar sound is recorded, though, the mixing engineers can add any effects they want to the signal and then re-play it through a miked guitar amplifier which is being recorded. The effects, amplifiers, cabinets, and miking processes can be changed to any combination. When a dry guitar has been recorded, it can be a useful tool for "updating" an older recording. For example, if a band wants to re-release a 1980s-era album on which the guitar has a very dated 1980s sound, with heavy flanging and artificial-sounding electronic distortion, the band can update the guitar sound by re-amping the dry signal and using 2000s-era effects.
Mixing guitar amp signals with other signals is also done by some musicians. Chris Squire
of Yes
produced his bass guitar sound by playing through a guitar amplifier with its bass turned down, treble turned up, and volume turned up well into distortion; the miked guitar speaker signal was then mixed with a direct-input (DI) signal, a technique that has been used for processing synth keyboards as well. A bass guitar can also be played through a bass amp in parallel with a distorted guitar amp by using a DI box; the bass amp provides the low frequencies, while the guitar amp – which is not capable of reproducing the lowest frequencies of the bass guitar– emphasizes the upper harmonics of the instrument's tone.
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...
designed to make the signal of an electric
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...
or acoustic guitar
Acoustic guitar
An acoustic guitar is a guitar that uses only an acoustic sound board. The air in this cavity resonates with the vibrational modes of the string and at low frequencies, which depend on the size of the box, the chamber acts like a Helmholtz resonator, increasing or decreasing the volume of the sound...
louder so that it will produce sound through 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...
. Most guitar amplifiers can also modify the instrument's tone by emphasizing or de-emphasizing certain frequencies and adding electronic effects.
Amplifiers consist of one or more circuit stages which have unique responsibilities in the modification of the input signal. The power amplifier
Amplifier
Generally, 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...
or output stage produces a high current signal to drive a speaker to produce sound. One or more preamplifier
Preamplifier
A preamplifier 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...
stages precede the power amplifier stage. The preamplifier is a voltage amplifier that amplifies the guitar signal to a level that can drive the power stage. There may be one or more tone stages which affect the character of the guitar signal: before the preamp stage (as in the case of guitar pedals), in between the preamp and power stages (as in the cases of effects loop or many dedicated amplifier tone circuits), in between multiple stacked preamp stages, or in feedback loops from a post-preamp signal to an earlier pre-preamp signal (as in the case of presence modifier circuits). The tone stages may also have electronic effects such as equalization
Equalization (audio)
Equalization is the process commonly used in sound recording and reproduction to alter the frequency response of an audio system using linear filters. Most hi-fi equipment uses relatively simple filters to make bass and treble adjustments. Graphic and parametric equalizers have much more...
, compression, distortion, chorus
Chorus effect
In music, a chorus effect occurs when individual sounds with roughly the same timbre and nearly the same pitch converge and are perceived as one...
, or 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...
. Amplifiers may use vacuum tubes (in Britain they are called valves), or solid-state (transistor) devices, or both.
There are two configurations of guitar amplifiers: combination ("combo") amplifiers, which include an amplifier and anywhere from one to four speakers in a wooden cabinet; and the standalone amplifier (often called a "head" or "amp head"), which does not include a speaker, but rather passes the signal to a speaker cabinet or "cab". Guitar amplifiers range in price and quality from small, low-powered practice amplifiers, designed for students, which sell for less than US$50, to expensive "boutique" amplifiers which are custom-made for professional musicians and can cost thousands of dollars.
History
The first electric instrument amplifiers were not designed for use with electric guitars. The earliest examples appeared in the early 1930s when the introduction of electrolytic capacitorElectrolytic capacitor
An electrolytic capacitor is a type of capacitor that uses an electrolyte, an ionic conducting liquid, as one of its plates, to achieve a larger capacitance per unit volume than other types. They are often referred to in electronics usage simply as "electrolytics"...
s and rectifier
Rectifier
A rectifier is an electrical device that converts alternating current , which periodically reverses direction, to direct current , which flows in only one direction. The process is known as rectification...
tubes
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
allowed the production of economical built-in power supplies
Power supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
that could be plugged into wall sockets, instead of heavy multiple battery packs
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
, since rechargeable batteries wouldn't be lightweight until later on. While guitar amplifiers from the beginning were used to amplify acoustic guitar
Acoustic guitar
An acoustic guitar is a guitar that uses only an acoustic sound board. The air in this cavity resonates with the vibrational modes of the string and at low frequencies, which depend on the size of the box, the chamber acts like a Helmholtz resonator, increasing or decreasing the volume of the sound...
, electronic amplification of guitar was first widely popularized by the 1930s and 1940s craze for Hawaiian music, which extensively employed the amplified lap steel Hawaiian guitar
Lap steel guitar
The lap steel guitar is a type of steel guitar, an instrument derived from and similar to the guitar. The player changes pitch by pressing a metal or glass bar against the strings instead of by pressing strings against the fingerboard....
.
Tone controls on early guitar amplifiers were very simple and provided a great deal of treble boost, but the limited controls, the loudspeakers used, and the low power of the amplifiers (typically 15 watts or less prior to the mid-1950s) gave poor high treble and bass output. Some models also provided effects
Effects unit
Effects 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...
such as spring reverb
Spring Reverb
Spring Reverb is the third studio album released by the rock and roll jam band The Big Wu. This was the last album recorded with former member Jason Fladager before he departed the band.-Track listing:# "Break of Day"# "SPMC"# "Make Believers"...
and/or an electronic tremolo
Tremolo
Tremolo, or tremolando, is a musical term that describes various trembling effects, falling roughly into two types. The first is a rapid reiteration...
unit. Early Fender amps labeled tremolo as "vibrato" and labeled the vibrato arm of the Stratocaster guitar as a "tremolo bar" (see vibrato unit
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....
, 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...
, and tremolo
Tremolo
Tremolo, or tremolando, is a musical term that describes various trembling effects, falling roughly into two types. The first is a rapid reiteration...
).
In the 1960s, guitarists experimented with distortion
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...
produced by deliberately overdriving their amplifiers. The Kinks
The Kinks
The Kinks were an English rock band formed in Muswell Hill, North London, by brothers Ray and Dave Davies in 1964. Categorised in the United States as a British Invasion band, The Kinks are recognised as one of the most important and influential rock acts of the era. Their music was influenced by a...
guitarist Dave Davies produced early distortion effects by connecting the already distorted output of one amplifier into the input of another. Later, most guitar amps were provided with preamplifier distortion controls, and "fuzz boxes" and other effects units were engineered to safely and reliably produce these sounds. In the 2000s overdrive and distortion has become an integral part of many styles of electric guitar playing, ranging from blues rock to 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 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...
.
Guitar amplifiers were at first used with bass guitars and electronic keyboard
Electronic keyboard
An electronic keyboard is an electronic or digital keyboard instrument.The major components of a typical modern electronic keyboard are:...
s, but other instruments produce a wider frequency range and need a suitable amplifier and full-range speaker system. Much more amplifier power is required to reproduce low-frequency sound, especially at high volume. Reproducing low frequencies also requires a suitable 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"...
or subwoofer
Subwoofer
A subwoofer is a woofer, or a complete loudspeaker, which is dedicated to the reproduction of low-pitched audio frequencies known as the "bass". The typical frequency range for a subwoofer is about 20–200 Hz for consumer products, below 100 Hz for professional live sound, and below...
speaker and enclosure
Loudspeaker enclosure
A loudspeaker enclosure is a purpose-engineered cabinet in which speaker drivers and associated electronic hardware, such as crossover circuits and amplifiers, are mounted...
. Woofer enclosures need to be larger and more sturdily built than cabinets for mid-range
Mid-range speaker
A loudspeaker driver that produces the frequency range from approximately 300–5000 hertz is known as a mid-range.Midrange drivers are usually cone types or, less commonly, dome types, or compression horn drivers...
or high-frequency (tweeter
Tweeter
A tweeter is a loudspeaker designed to produce high audio frequencies, typically from around 2,000 Hz to 20,000 Hz . Some tweeters can manage response up to 65 kHz...
) speakers.
Types
Guitar speaker
A guitar speaker is a loudspeaker – specifically the driver part – designed for use in or with the guitar amplifier of an electric guitar...
s in a single unit which is typically housed in a rectangular wooden box. The amplifier head or "amp head" contains the electronic circuitry constituting the preamp, built-in effects processing, and the power amplifier. Combo amps have at least one 1/4" input jack where the patch cord from the electric guitar can be plugged in. Other jacks may also be provided, such as an additional input jack, "send" and "return" jacks to create an effects loop (for connecting electronic effects such as compression, reverb, etc.), an extension speaker jack (for connecting an additional speaker cabinet). Some smaller practice amps have stereo RCA jacks for connecting a CD player, iPod
IPod
iPod is a line of portable media players created and marketed by Apple Inc. The product line-up currently consists of the hard drive-based iPod Classic, the touchscreen iPod Touch, the compact iPod Nano, and the ultra-compact iPod Shuffle...
or other sound source and a 1/4" headphone jack so that the player can practice without disturbing neighbours or family members.
Some amplifiers have a line out jack for connecting the amplifier's signal to a PA system or recording console or to connect the amplifier to another guitar amp. In but most styles of rock and blues guitar, the line out is not used to connect the guitar amp to a PA system or recording console, because the tonal coloration and overdrive from the amplifier and speaker is considered an important part of the amplifier's sound. However, players do use the line out to connect one guitar amplifier to another amplifier, in order to create different tone colors or sound effects.
In the "amp head" form, the amplifier head is separate from the speakers, and joined to them by speaker cables. The separate amplifier is called an amplifier head, and is commonly placed on top of one or more loudspeaker enclosures. A separate amplifier head placed atop a guitar speaker enclosure or guitar speaker cabinet forms an amplifier "stack" or "amp stack". Amp heads may also have the different types of input and output jacks listed above in the combo section. In addition to a 1/4" input jack, acoustic guitar amplifiers typically have an additional input jack for a microphone
Microphone
A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...
, which is easily identified because it will use a three-pin XLR connector
XLR connector
The XLR connector is a style of electrical connector, primarily found on professional audio, video, and stage lighting equipment. The connectors are circular in design and have between 3 and 7 pins...
. Phantom power
Phantom power
Phantom power, in the context of professional audio equipment, is a method for transmitting DC electric power through microphone cables to operate microphones that contain active electronic circuitry....
is not often provided on general-use amps, restricting the choice of microphones for use with these inputs. However, for high-end acoustic amplifiers, phantom power is often provided, so that musicians can use condenser microphones.
Amplifiers used with electric guitars may be solid-state, which are lighter in weight and less expensive than tube amplifiers. Most guitarists, particularly in the genres of blues and rock, prefer the sound of vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
amplifiers despite their higher cost, heavier weight, the need to periodically replace tubes and need to re-bias the output tubes (every year or two with moderate use). Some companies design amplifiers that require no biasing as long as properly rated tubes are used. Some modern amplifiers use a mixture of tube and solid-state technologies.
Since the advent of microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
s and digital signal processing, "modeling amps" have been developed in the late 1990s, these can simulate the sounds of a variety of well-known tube amplifiers without needing to use vacuum tubes. Amplifiers with processors and software emulate the sound of a classic amp well, but from the player's point of view the response of these amplifiers may not feel the same as the digital modeling does not accurately model all aspects of a tube amplifier.
A wide range of instrument amplifiers is available, some for general purposes and others designed for specific instruments or particular sounds. These include:
- "Traditional" guitar amplifiers, with a clean, warm sound, a sharp treble roll-offRoll-offRoll-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 or less and bass roll-off at 60–100 Hz, and often built-in reverbReverberationReverberation 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 tremolo (sometimes incorrectly called 'vibrato') units. These amplifiers, such as the Fender "Tweed"-style amps, are often used by traditional rock, blues, and country musicians. Traditional amps have more recently become popular with musicians in indie and alternative bands - Hard rock-style guitar amplifiers, which often include preamplification controls, tone filters, and distortion effects that provide the amplifier's characteristic tone. Users of these amplifiers use the amplifier's tone to add "drive", intensity, and "edge" to their guitar sound. Amplifiers of this type, such as Marshall amplifiers, are used in a range of genres, including hard rock, metal, and punk.
- Bass amplifiers, with extended bass response and tone controls optimized for bass guitars (or more rarely, for upright bass). 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. Bass amplifiersBass 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...
are often provided with external metal heat sinks or fans to help keep the amplifier cool. - Acoustic amplifiers, similar in many ways to keyboard amplifiers but designed specifically to produce a "clean," transparent, "acoustic" sound when used with acoustic instruments with built-in transducer pickups and/or microphones.
Vacuum tube amplifiers
Triode
A triode is an electronic amplification device having three active electrodes. The term most commonly applies to a vacuum tube with three elements: the filament or cathode, the grid, and the plate or anode. The triode vacuum tube was the first electronic amplification device...
s are used in the preamplifier section in order to provide sufficient voltage gain to offset losses by tone controls and to drive the power amplifier section.
Push-pull output
A push–pull output is a type of electronic circuit that can drive either a positive or a negative current into a load. Push–pull outputs are present in TTL and CMOS digital logic circuits and in some types of amplifiers, and are usually realized as a complementary pair of transistors, one...
connection to improve efficiency; this requires another triode or dual triode to split the phase
Phase (waves)
Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...
of the signal. The tubes of the power amplifier stage are almost always of the pentode
Pentode
A pentode is an electronic device having five active electrodes. The term most commonly applies to a three-grid vacuum tube , which was invented by the Dutchman Bernhard D.H. Tellegen in 1926...
or beam tetrode
Beam tetrode
A beam tetrode is a type of vacuum tube specially designed to produce greater output power than a similar pentode...
type (also known as "kinkless tetrodes", hence the KTxx nomenclature). Some high power models use paralleled pairs of output tubes (four or more in total) in push-pull. Except for the light negative feedback
Negative feedback
Negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...
from the secondary end of the output transformer to the driver stage, most amplifying stages work in "raw" open-loop mode. Some designs employ current feedback via unbypassed cathode resistors.
Since most tubes show "soft clipping" gain non-linearity, applying an input signal high enough to overdrive any stage tends to produce favorably natural distortion. Today, most vacuum tube amplifiers are based on the ECC83/12AX7
12AX7
12AX7 is a miniature dual triode vacuum tube with high voltage gain. It was developed around 1946 by RCA engineers in Harrison, New Jersey, under developmental number A-4522. It was released for public sale under the 12AX7 identifier on September 15, 1947. The 12AX7 was originally intended as...
/7025 (dual triode) tubes for the preamplifier and driver sections and the EL84
EL84
The EL84 is a vacuum tube of the power pentode type. It has a 9 pin Noval base and is found mainly in the final output stages of amplification circuits, most commonly now in guitar amplifiers, but originally in radios and many other devices of the pre-transistor era.It was developed to eliminate...
/6BQ5 or EL34
EL34
The EL34 is a thermionic valve or vacuum tube of the power pentode type. It has an international octal base and is found mainly in the final output stages of audio amplification circuits and was designed to be suitable as a series regulator by virtue of its high permissible voltage between heater...
/6CA7/KT77 or 6L6
6L6
6L6 is the designator for a vacuum tube introduced by Radio Corporation of America in July 1936. At the time Philips had already developed and patented power pentode designs, which were fast replacing power triodes due to their greater efficiency...
/KT66 or 6V6
6V6
The 6V6 is a beam-power tetrode, introduced by Radio Corporation of America RCA United States in late 1937, and still in use in niche applications.Similar to its predecessor the 6L6, the 6V6 was far more widely used...
tubes for the power output section. Some use the KT88
KT88
The KT88 is a beam tetrode/kinkless tetrode vacuum tube for audio amplification.- Features :The KT88 fits a standard eight-pin octal socket and has similar pinout and applications as the 6L6 and EL34. Specifically designed for audio amplification, the KT88 has similar ratings to the American 6550...
/6550 beam power
Beam tetrode
A beam tetrode is a type of vacuum tube specially designed to produce greater output power than a similar pentode...
tubes in the output stage. The differing codes for equivalent tubes generally reflect those used by the original European or U.S.A. based manufacturers. These tubes are now mainly manufactured in Russia, China and Eastern European countries. Some amplifiers, such as the Marshall Silver Jubilee, use solid-state components in the preamp, most commonly diodes, to create distortion, a design feature known as diode clipping.
Tube instrument amplifiers are often equipped with lower-grade transformers and simpler power regulation circuits than those of hi-fi amplifiers. They are usually not only for cost-saving reasons, but also are considered as a factor in sound creation . For example, a simple power regulation circuit's output tends to sag when there is a heavy load (that is, high output power) and vacuum tubes usually lose gain factors with lower power voltages. This results in a somewhat compressed sound which could be criticized as a "poor dynamic range" in case of hi-fi amplifiers, but could be desirable as "long sustain" of sounds on a guitar amplifier. Some tube guitar amplifiers use a rectifier
Rectifier
A rectifier is an electrical device that converts alternating current , which periodically reverses direction, to direct current , which flows in only one direction. The process is known as rectification...
tube instead of solid-state diodes specifically for this reason.
Unfortunately, most amplifiers offer a fixed amount of sag, and this fixed amount can only be attained at full volumes. A small minority of amplifiers offer sag control via either multiple rectifiers or the Sag Circuit (a non-traditional power supply design patented by Maven Peal® Instruments). Amplifiers with multiple rectifiers can offer up to two sag settings (amounts), while the Sag Circuit provides a Sag control knob, which allows range of sag control at all volumes (by interacting with a wattage control knob).
Some models have a "spring reverb" unit that simulates the reverberation
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...
of an echoic ambient. A reverb unit usually consists of one or more coil springs driven by the preamplifier section using a transducer driver similar to a loudspeaker at one end and an electro-magnetic pickup and preamplifier stage at the other end that picks up the long sustaining spring vibration, which is then mixed with the original signal. Some guitar amplifiers have a tremolo
Tremolo
Tremolo, or tremolando, is a musical term that describes various trembling effects, falling roughly into two types. The first is a rapid reiteration...
control. An internal oscillator generates a low frequency continuous signal which can modulate the input signal's amplitude or the output tubes' bias, thereby producing a tremolo effect.
Tube amps have the following technical disadvantages in comparison to solid-state amps. They are bulky and heavy, primarily due to the iron in power and output transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
s. Solid-state amplifiers still require power transformers, but are usually direct-coupled and don't need output transformers. Glass tubes are fragile, and require more care and consideration when equipment is moved repeatedly. Tube performance can deteriorate slightly over time before eventual catastrophic failure.
When tube vacuum is maintained at a high level, though, excellent performance and life is possible. They are prone to pick up mechanical noises (microphonic noise
Microphonics
Microphonics describes the phenomenon where certain components in electronic devices transform mechanical vibrations into an undesired electrical signal...
), although such electro-mechanical feedback from the loudspeaker to the tubes in combo amplifiers may contribute to sound creation. Tubes benefit from a heater warm-up period before the application of high tension anode voltages; this allows the tube cathodes to operate without damage and so prolongs tube life. This is of particular importance for amplifiers with solid-state rectifiers.
Tube amps have the following technical advantages over solid-state amps. Compared to semiconductors, tubes have a very low "drift" (of specs) over a wide range of operating conditions, specifically high heat/high power. Semiconductors are very heat-sensitive by comparison and this fact usually leads to compromises in solid-state amplifier designs. When a tube fails, it is replaceable. While solid-state devices are also replaceable, it is usually a much more involved process (i.e., having the amplifier tested by a professional, removing the faulty component, and replacing it).
For working musicians this is usually a huge problem by comparison to looking in the back of a tube amp at the tubes and simply replacing the faulty tube. In addition, tubes can easily be removed and tested, while transistors cannot. Tube amplifiers respond differently from transistor amplifiers when signal levels approach and reach the point of clipping
Clipping (audio)
Clipping is a form of waveform distortion that occurs when an amplifier is overdriven and attempts to deliver an output voltage or current beyond its maximum capability...
. In a tube-powered amplifier, the transition from linear amplification to limiting is less abrupt than in a solid-state unit, resulting in a less grating form of distortion at the onset of clipping. For this reason, some guitarists prefer the sound of an all-tube amplifier; the aesthetic properties of tube versus solid-state amps, though, are a topic of debate in the guitarist community.
Solid-state amplifiers
Most inexpensive guitar amplifiers currently produced are based on semiconductorSemiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
(solid-state) circuits, and some designs incorporate tubes in the preamp stage for their subjectively warmer overdrive sound. Tubes create warm overdrive sounds because instead of cutting the peaked signal off, they more or less pull the peaked audio information back (like natural compression) which creates a fuzzy overdrive sound. While this is a desirable attribute in many cases, the tube's characteristic will "color" all the sounds at any volume, unlike solid-state.
High-end solid-state amplifiers are less common, since many professional guitarists tend to favor vacuum tubes. Some jazz guitarists, however, tend to favor the "cleaner" sound of solid-state amplifiers, preferring not to color the sound of their guitar with the tube distortion and compression so popular with rock, blues, and metal musicians.. Solid-state amplifiers vary in output power, functionality, size, price, and sound quality in a wide range, from practice amplifiers to professional models. Some inexpensive amplifiers have only a single volume control and a one or two tone controls .
Hybrid amplifiers
A tube power amp may be fed by a solid-state pre-amp circuit, as in most of the Original MusicManMusic Man (company)
Music Man is an American guitar, and bass guitar manufacturer. It is a division of the Ernie Ball corporation.-Early years:The Music Man story began in 1971 when Forrest White and Tom Walker talked with Leo Fender about starting a company they would call Tri-Sonic, Inc...
Amps, Fender Super Champ XD and the Roland Bolt amplifier, which is thereby classed as a 'hybrid' amp. Randall Amplifier's
Randall Amplifiers
Randall Amplifiers is a manufacturer of guitar amplifiers, a subsidiary of U.S. Music Corporation. Its products are/were used by artists such as Chuck Schuldiner, Dimebag Darrell, Metallica, King's X, Nirvana and Anthrax...
current flagship models, the V2 and T2, use hybrid amp technology. Alternatively, a tube pre-amp can feed a solid-state output stage, as in models from Kustom
Kustom
Kustom Amplification or Kustom Electronics is a manufacturer of guitar and bass amplifiers and PA equipment and accessories based in Hebron, Kentucky. It is part of the Hanser Music Group as of 1999, which also includes B.C. Rich Guitars, and Traben Bass.- History :"Kustom" was a brand and...
and Vox
Vox
Vox is Latin for Voice. It may refer to:* Vocals, a common abbreviation, especially in pro audio-Music:* "Vox" , a song by Sarah McLachlan* Vox Records, an American record label* Vox Records , a German record label...
. This approach dispenses with the need for an output transformer and allow modern power levels to be easily achieved.
Modeling amplifiers
Modeling amplifiers use amplifier modelingAmplifier modeling
Amplifier modeling is the process of digitally emulating a physical amplifier such as a guitar amplifier. Amp modeling may appear as software, such as plugins for DAWs which may be aided by computer hardware accelerators, or may be part of a standalone device or amplifier...
to simulate the sound of well-known guitar amps, cabinets, and effects, as well as simulating the way traditional speaker cabinets sound when mixed with different types of microphones. They may also be an original creation not meant to simulate any particular real world guitar amp at all, instead allowing the user to create their own unique sound. Such as the original creations of companies like AcmeBarGig or Peavey
Peavey Electronics
Peavey Electronics Corporation is one of the largest audio equipment manufacturers in the world, headquartered in Meridian, Mississippi in the United States.- History :...
. This is usually achieved through digital processing. Modeling technology offers several advantages over traditional amplification. A modeling amp typically is capable of a wide range of tones and effects, and offers cabinet simulation, so it can be recorded without a microphone. Most modeling amps digitize the input signal and use a DSP
Digital signal processor
A digital signal processor is a specialized microprocessor with an architecture optimized for the fast operational needs of digital signal processing.-Typical characteristics:...
, a dedicated microprocessor, to process the signal with digital computation. Some modeling amps incorporate vacuum tubes, digital processing, and some form of power attenuation.
Acoustic guitar amplifiers
These amplifiers are designed to be used with acoustic guitars, 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.
Amplifier configuration
In heavy metal bands, the term "double stack" or "full stack" is sometimes used to refer to two stacks, with the main amplifier section of a second amplifier serving as a slave to the first and four speaker cabinets in total. Another name for the "Head & Cab" that comes from the 1960s and 1970s is "Piggyback". Vox amp stacks could be put on a tiltable frame with casters. Fender heads could be attached to the cab and had "Tilt-Back" legs, like those used on larger Fender combo amps. Typically, a guitar amp's preamplifier section (known as a 'pre') provides sufficient gain so that an instrument can be connected directly to its input, and its main amplification section (known as the 'power stage') sufficient power
Power (physics)
In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...
to connect loudspeakers directly to its output
Output
Output is the term denoting either an exit or changes which exit a system and which activate/modify a process. It is an abstract concept, used in the modeling, system design and system exploitation.-In control theory:...
, both without requiring extra amplification.
Some touring bands have used the appearance of a large array of guitar amplifiers for aesthetic reasons. Some of these arrangements include one or more actual guitar cabinets, while others do not. In reference to a photograph (left) taken during an Immortal
Immortal (band)
Immortal is a black metal band from Bergen, Norway, founded in 1990 by current frontman/guitarist Abbath Doom Occulta and former guitarist Demonaz Doom Occulta...
gig, showing that what appeared to the audience to be a wide formation of equipment was actually only the fronts of amplifiers mounted on a large frame, Gizmodo
Gizmodo
Gizmodo is a technology weblog about consumer electronics. It is part of the Gawker Media network run by Nick Denton and is known for its up-to-date coverage of the technology industry, along with topics as broad as design; architecture; space and science....
writer Rosa Golijan investigated the phenomenon and found that it was "not too uncommon".
Another arrangement, often used for public address
Public address
A public address system is an electronic amplification system with a mixer, amplifier and loudspeakers, used to reinforce a sound source, e.g., a person giving a speech, a DJ playing prerecorded music, and distributing the sound throughout a venue or building.Simple PA systems are often used in...
amplifier systems, is to provide two stages of amplification in separate units. First a preamplifier
Preamplifier
A preamplifier 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...
or mixer is used to boost the instrument output, normally to line level
Line level
Line level is a term used to denote the strength of an audio signal used to transmit analog sound between audio components such as CD and DVD players, TVs, audio amplifiers, and mixing consoles, and sometimes MP3 players....
, and perhaps to mix signals from several instruments. The output
Output
Output is the term denoting either an exit or changes which exit a system and which activate/modify a process. It is an abstract concept, used in the modeling, system design and system exploitation.-In control theory:...
from this preamplifier is then connected to the input of a power amplifier, which powers the loudspeakers.
Performing musicians that use the "two-stage" approach (as opposed to an amplifier with an integrated preamplifier and power amplifier) often want to custom-design a combination of equipment that best suits their musical or technical needs, and gives them more tonal and technical options. Some musicians require preamps that include specific features. Acoustic performers sometimes require preamps with "notch" filters (to prevent feedback), reverb, an XLR DI output, or parametric equalization. Hard rock, metal, or punk performers may desire a preamplifier with a range of distortion effects. As well, some musicians have specific power amplifier requirements, such as low-noise design, very high wattage, the inclusion of limiter features to prevent distortion and speaker damage, or biamp-capable operation.
With the "two-stage" approach, the preamplifier and power amplifier are often mounted together in a rack case
19-inch rack
A 19-inch rack is a standardized frame or enclosure for mounting multiple equipment modules. Each module has a front panel that is wide, including edges or ears that protrude on each side which allow the module to be fastened to the rack frame with screws.-Overview and history:Equipment designed...
. This case may be either free-standing or placed on top of a loudspeaker cabinet. If many rack-mounted effects are used, the rack may be a large unit on wheels. Some touring players need several racks of effects units to reproduce on stage the sounds they have produced in the studio. At the other extreme, if a small rack case containing both preamp and power amp is placed on top of a guitar speaker cabinet, the distinction between a rack and a traditional amp head begins to blur. Another variation is to combine the power amplifier into the speaker cabinet, an arrangement called a powered speaker, and use these with a separate preamp, sometimes combined into an effects pedal board or floor preamp/processor.
Preamplifiers are also used to connect very low-output or high-impedance
Electrical impedance
Electrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...
instruments to instrument amplifiers. When piezoelectric transducers are used on upright bass or other acoustic instruments, the signal coming directly from the transducer is often too weak and it does not have the correct impedance for direct connection to an instrument amplifier. Small, battery-powered preamps are often used with acoustic instruments to resolve these problems.
Power output
For electric guitar amplifiers, there is often a distinction between "practice" or "recording studio" guitar amps, which tend to have output power ratings of 20 watts down to a small fraction of a watt, and "performance" amps, which are generally 50 watts or higher. Traditionally, these have been fixed-power amplifiers, with a few models having a half-power switch to slightly reduce the listening volume while preserving power-tube distortion. The relationship between perceived volume and power output is not immediately obvious. A 5-watt amplifier is perceived to be half as loud as a 50-watt amplifier (a tenfold increase in power), and a half-watt amplifier is a quarter as loud as a 50-watt amp. Doubling the power of an amplifier results in a "just noticeable" increase in volume, so a 100-watt amplifier is held to be only just noticeably louder than a 50-watt amplifier. Such generalizations are also subject to the human ear's tendency to behave as a natural compressor at high volumes.Power attenuation can be used with either low-power or high-power amplifiers, resulting in variable-power amplifiers. A high-power amplifier with power attenuation can produce power-tube distortion through a wide range of listening volumes. Speaker efficiency is also a major factor affecting a tube amplifier's maximum volume. For bass instruments, higher-power amplifiers are needed to reproduce low-frequency sounds. While an electric guitarist would be able to play at a small club with a 50-watt amplifier, a bass player performing in the same venue would probably need an amplifier with 200 or more watts.
Distortion and volume
DistortionDistortion (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...
is a feature available on many guitar amplifiers that is not typically found on keyboard or bass guitar amplifiers. Tube guitar amplifiers can produce distortion through pre-distortion equalization, preamp tube distortion, post-distortion EQ, power-tube distortion, tube rectifier compression, output transformer distortion, guitar speaker distortion, and guitar speaker and cabinet frequency response. Distortion sound or "texture" from guitar amplifiers is further shaped or processed through the frequency response and distortion factors in the microphones (their response, placement, and multi-microphone comb filtering effects), microphone preamps, mixer channel equalization, and compression. Additionally, the basic sound produced by the guitar amplifier can be changed and shaped by adding distortion and/or equalization effect pedals before the amp's input jack, in the effects loop just before the tube power amp, or after the power tubes.
Power-tube distortion
Power-tube distortion is required for amp sounds in some genres. In a standard master-volume guitar amp, as the amp's final or master volume is increased beyond the full power of the amplifier, power tube distortion is produced. The "power soak" approach places the attenuation between the power tubes and the guitar speaker. In the re-amped or "dummy load" approach, the tube power amp drives a mostly resistive dummy load while an additional low power amp drives the guitar speaker. In the isolation box approach, the guitar amplifier is used with a guitar speakerGuitar speaker
A guitar speaker is a loudspeaker – specifically the driver part – designed for use in or with the guitar amplifier of an electric guitar...
in a separate cabinet. A soundproofed isolation cabinet
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...
, isolation box, isolation booth, or isolation room can be used.
Volume controls
A variety of labels are used for level attenuation potentiometers in a guitar amplifier and other guitar equipment. Electric guitars and basses have a volume control to attenuate whichever pickup is selected. There may be two volume controls in parallel to mix the signal levels from the neck and bridge pickups. Rolling back the guitar's volume control also changes the pickup's equalization or frequency response, which can provide pre-distortion equalization.The simplest guitar amplifiers have only a volume control. Most have at least a gain control and a master volume control. The gain control is equivalent to the distortion control on a distortion pedal, and similarly may have a side-effect of changing the proportion of bass and treble sent to the next stage.
A simple amplifier's tone controls typically include passive bass and treble controls. In some cases, a midrange control is provided. The amplifier's master volume control restricts the amount of signal permitted through to the driver stage and the power amplifier. When using a power attenuator with a tube amplifier, the master volume no longer acts as the master volume control. Instead, the power attenuator's attenuation control controls the power delivered to the speaker, and the amplifier's master volume control determines the amount of power-tube distortion. Power-supply based power reduction is controlled by a knob on the tube power amp, variously labeled "Wattage", "Power", "Scale", "Power Scale", or "Power Dampening".
Use with other instruments
Musicians often run sound-sources other than guitars through guitar amps. For live performances, synthesizers and drum machines or keyboards are often put through guitar amps to create a richer sound than can be obtained by patching the direct-outs right into the PA system. Guitar amplifiers can add tonal coloration, roll off unwanted high frequencies, and add overdrive or distortion. Deep PurpleDeep Purple
Deep Purple are an English rock band formed in Hertford in 1968. Along with Led Zeppelin and Black Sabbath, they are considered to be among the pioneers of heavy metal and modern hard rock, although some band members believe that their music cannot be categorised as belonging to any one genre...
's Jon Lord
Jon Lord
Jonathan Douglas "Jon" Lord is an English composer, pianist and Hammond organ player.Jon Lord, also known as 'Hammond Lord', is a classically trained piano player. He is recognised for his Hammond organ blues-rock sound and for his pioneering work in fusing rock and classical or baroque forms...
played his Hammond Organ
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...
through a distorted Marshall
Marshall Amplification
Marshall Amplification is a British company, founded by drummer Jim Marshall, that designs and manufactures music amplifiers, brands personal headphones/earphones , and, after acquiring Natal Drums, drums and bongos. Marshall amplifiers, and specifically their guitar amplifiers, are among the most...
amp to create a sound more suitable for heavy rock. String instruments and vocals are also put through guitar amps to add distortion effects. Some blues harp
Blues harp
The Richter-tuned harmonica, or 10-hole harmonica or blues harp , is the most widely known type of harmonica...
players also use guitar or bass amps to create a warmer overdrive sound for their harmonica playing; 1950s-style "tweed" amps are often used for this purpose, such as Fender Bassman combo amps.
Recording engineers occasionally run pre-recorded parts through miked guitar amps, a process called re-amping. When a guitar part is recorded "dry" (e.g., without effects or distortion), straight into the mixing board for a recording, this gives the producer and mixing engineer much more flexibility to create new re-mixes or new tones from the recording. If a guitar player records an electric guitar part that is run through a chorus pedal and a distortion pedal, there is little that can be done at the "mix-down" stage to change the sound of this recording, beyond "tweaking" the equalization and modifying the level. Since re-mixing or mixdown can take place weeks, months, or even years after the original recording session, it may be impossible to have the guitarist come in to re-record a new part.
If the dry guitar sound is recorded, though, the mixing engineers can add any effects they want to the signal and then re-play it through a miked guitar amplifier which is being recorded. The effects, amplifiers, cabinets, and miking processes can be changed to any combination. When a dry guitar has been recorded, it can be a useful tool for "updating" an older recording. For example, if a band wants to re-release a 1980s-era album on which the guitar has a very dated 1980s sound, with heavy flanging and artificial-sounding electronic distortion, the band can update the guitar sound by re-amping the dry signal and using 2000s-era effects.
Mixing guitar amp signals with other signals is also done by some musicians. Chris Squire
Chris Squire
Christopher Russell Edward "Chris" Squire , is an English musician, known as the bass guitarist and backing vocalist for the progressive rock group Yes. He is the only member of the group to appear on every album.-Before Yes:...
of Yes
Yes (band)
Yes are an English rock band who achieved worldwide success with their progressive, art, and symphonic style of rock music. Regarded as one of the pioneers of the progressive genre, Yes are known for their lengthy songs, mystical lyrics, elaborate album art, and live stage sets...
produced his bass guitar sound by playing through a guitar amplifier with its bass turned down, treble turned up, and volume turned up well into distortion; the miked guitar speaker signal was then mixed with a direct-input (DI) signal, a technique that has been used for processing synth keyboards as well. A bass guitar can also be played through a bass amp in parallel with a distorted guitar amp by using a DI box; the bass amp provides the low frequencies, while the guitar amp – which is not capable of reproducing the lowest frequencies of the bass guitar– emphasizes the upper harmonics of the instrument's tone.
See also
- List of guitar amplifier manufacturers
- 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 :...
- Instrument amplifierInstrument amplifierAn 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...
- 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...
- 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...
- Valve sound
- Guitar effects
- Guitar speaker cabinet
- Re-ampRe-ampReamping is a process often used in multitrack recording in which a recorded signal is routed back out of the editing environment and run through external processing or reverb chamber...
Further reading
- Weber, Gerald, "A Desktop Reference of Hip Vintage Guitar Amps", Hal Leonard Corporation, 1994. ISBN 0964106000
External links
- Duncan's amp pages — All sorts of information, especially on tube guitar amplifiers.
- AX84 — Learn to build your own tube guitar amplifier with free schematics and plans.
- Amplified Parts Tech Corner — Technical resources and diagrams for modifying and repairing guitar amps
- Photos of Vintage Tube Guitar Amplifiers
- Rebuilding a Fender Deluxe Reverb Tube Amplifier - Information on modification and conversion of amplifiers