What are amps made of?
This article includes a list of references, related reading or
external links, but its sources remain unclear because it lacks
inline citations. Please improve this article by introducing more
precise citations. (September 2009) Mesa Boogie Mark IV, a guitar
combo amplifier A guitar amplifier (or guitar amp) 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. Contents [hide] 1 History 2 Types 2.1 Vacuum
tube amplifiers 2.2 Solid-state amplifiers 2.3 Hybrid amplifiers
2.4 Modeling amplifiers 2.5 Acoustic guitar amplifiers 3 Amplifier
configuration 4 Distortion, power, and volume 4.1 Power output 4.2
Distortion and volume 4.2.1 Power-tube distortion 4.3 Volume
controls 5 Use with other instruments 6 See also 7 References 8
Further reading 9 External links [edit]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 capacitors 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 keyboards, 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.
[edit]Types Two combo amplifiers Guitar amplifiers are manufactured
in two main forms. The "combination" (or "combo") amplifier
contains the amplifier head and guitar speakers 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. Kustom 200 bass amp - amp head and speakers, 100 watts
RMS, two channels, two 15" speakers, 1971 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 microprocessors 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-off at 5 kHz or less and
bass roll-off at 60-100 Hz, and often built-in reverb 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 amplifiers 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. [edit]Vacuum tube amplifiers Main
article: Valve amplifier The glow from four "Electro Harmonix KT88"
brand power tubes lights up the inside of a Traynor YBA-200 bass
guitar amplifier 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 triodes
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. Rear view of a tube (valve) combo guitar
amplifier. Visible are two glass output tubes, six smaller preamp
tubes in their metal tube retainers, and both the power transformer
and the output transformer. 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[citation needed]. 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
transformers. 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. [edit]Solid-state amplifiers This article's
Criticism or Controversy section may compromise the article's
neutral point of view of the subject. Please integrate the
section's contents into the article as a whole, or rewrite the
material; see the discussion on the talk page. (October 2011) Most
inexpensive guitar amplifiers currently produced are based on
semiconductor (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
"colder" 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.[citation needed].
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[citation
needed]. [edit]Hybrid amplifiers A tube power amp may be fed by a
solid-state pre-amp circuit, as in the 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. The Roland Micro
Cube, left, a small and portable digital modeling amplifier.
[edit]Modeling amplifiers Modeling amplifiers use amplifier
modeling 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. [edit]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 folk 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. [1] [edit]Amplifier configuration A 3 x 6
stack of Marshall guitar cabinets for Jeff Hanneman of Slayer 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".[2] 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. [edit]Distortion, power, and volume
[edit]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. [edit]Distortion and volume Distortion 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. [edit]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 speaker in a
separate cabinet. A soundproofed isolation cabinet, isolation box,
isolation booth, or isolation room can be used. [edit]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". [edit]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 Purple'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.
[edit]See also List of guitar amplifier manufacturers Power
attenuator (guitar) Instrument amplifier Bass instrument
amplification Electronic amplifier Valve sound Guitar effects
Guitar speaker cabinet Re-amp [edit]References ^ Note: This style
of amplifiers should not be confused with the brand of guitar and
bass amplifiers called Acoustic, still available in second-hand
music stores.) ^ Golijan, Rosa (22 September 2010). "The Concert
Speakers Are A Lie". Gizmodo. Retrieved 16 January 2011.
[edit]Further reading Weber, Gerald, "A Desktop Reference of Hip
Vintage Guitar Amps", Hal Leonard Corporation, 1994. ISBN
0964106000 [edit]External links Wikimedia Commons has media related
to: Guitar Wikibooks has a book on the topic of Guitar/Buying an
amplifier Guitar portal 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 [show]v · d · eGuitars [show]v · d · eMusic
technology
