Guitar amplifier

A guitar amplifier is an electronic device for amplifying the sound of a guitar or an electric guitar.

The signal of the Gitarrentonabnehmers is transmitted via a cable or via a radio apparatus to the amplifier. The guitar amp is not to amplify sound neutral in the case of the electric guitar, but also contribute significantly to the sound education. The musician looks at the guitar amp often as part of his musical instrument and uses it to give his game expression.

Building a guitar amp

The individual components of a guitar amp are the input (signal input), mostly realized by a connection with a 6.35 -mm mono jack, preamp with volume control ( "Gain" ), tone control (equalizer) to boost or cut individual frequency ranges (bass, middle, treble) (linear distortion), output amplifier, speaker system, power supply ( PSU ).

For example, the speaker system usually consists of 8 "to 15 " (inch) speakers so is a typical Marshallbox with 4 speakers, each equipped 12 " and loaded with 100 to over 400 watts RMS power.

In many devices, a so-called Reverb ( spring reverb ) is installed for generating artificial reverberation. Chance of additional effects such as chorus and tremolo can be integrated.

Guitar amplifiers come in various power levels of about 2 watts ( Roland Microcube ) to over 350 watts ( Marshall Mode Four ) output power. Even greater power outputs are not useful in general, as in bigger stage installations, the instruments are transmitted via the PA system.

Nonlinear distortion

A non-linear distortion of the signal is desired in certain types of pop music, especially in rock music and is achieved by selectively overdriving the guitar amplifier or individual amplifier stages within the guitar amp. The override of the precursor is described by the manufacturers as Distortion, overdriving the output stage is referred to as overdrive. It can be used in combination and influence in the signal chain. The distortion can also occur outside of the guitar amp in upstream effectors, generally through a distortion box.

The distortion in the preliminary stage compresses the signal stronger ( such as the heavy metal used ), while power amp distortion here more dynamic, similar to the clean sound, remains ( such as in blues / rock ).

The distorted operation of all levels of guitar amplifier operates without special measures in operation at very high volume. If this is not desired, but to distort but the entire amplifier, the loudspeaker can be a resistor network is connected upstream, which converts the major part of the output signal to the heat and the loudspeaker, only a fraction of the output power feeding ( power soak ). Alternatively, performs a power reduction in the output stage ( eg by reducing the operating voltage of the tubes) to the desired result. In all cases, however, it must be remembered that inevitably decline with a decrease in the overall volume of the nonlinear distortions of the loudspeaker, which also contribute to sound like the distortion of the output stage.

Guitar amplifiers usually have multiple signal paths ( " channels") with different sound characteristics. A common so-called clean channel only has a volume adjuster, sometimes even combined with a tone setting. A channel with more distortion usually has a so-called gain adjuster that affects the strength of the distortion degree, coupled with a volume adjuster for the output volume. The channels can be selected by pressing a button on the amplifier or with a foot switch.

Types

Combo Amplifier

Combo amplifier (abbreviated Combo ), the electronics and one or more loudspeakers mounted in a common housing. The first early guitar amplifiers were mostly of this type. The rear housing may be opened or closed, which has an effect on the sound characteristics of the speaker. Smaller combos are easier to handle than other types. Larger appliances, such as the Fender Twin Reverb are heavier to carry, since all components have to be moved at a time. The output power moves in generally in the range of 5 to 100 watts. Combos with even smaller output power can also be supplied from a battery to some extent. They are well suited for practice and game locations without AC power supply. Some combos can also be used with a headset, such as the Rockman, which was developed by Tom Scholz, founder of the rock band Boston, in the 1980s.

Examples of Combo Amplifier Fender Twin Reverb
Marshall Bluesbreaker
Vox AC30
Roland Jazz Chorus JC -120
Orange Rockerverb 50C

Amp Head & Speakers

Are amplifier and box separately, then one speaks of top speaker (English Head ) and Box (English Cabinet). If the items referred stacked, one speaks of a tower (English stack). Here are subdivided in turn into a Half- Stack ( amp with a box ) and a full-stack ( amp is at 2 boxes). In the boxes of the so-called stacks are usually to units with 4 x 12 " guitar speaker. However, there are 1 × 12 "- 2 × 12 " - or 4 × 10 "boxes.

Examples of ( top part ) Marshall Plexi
Mesa / Boogie Mark IV
Engl Savage 120
Orange Thunderverb 200H

Rack ( Pre & Power Amplifier )

In traditional amplifiers and power amp form a unit. There are also numerous variations in which form pre and power amp of your units. These are usually mounted in a 19 "(inch) rack systems.

Examples ( precursor) Marshall JMP 1
Mesa / Boogie Triaxis

Examples (output stage ) Mesa / Boogie Strategy 500
Peavey Classic 50/50

Tube

In tube amplifiers for amplifying the signal electron tubes are used. Although nowadays rarely used in electronics tubes ( due to size, weight, heat generation, long-term stability and complex power supply) that is on guitar amps due to the special transmission characteristics not always the case.

About the dynamics beyond walking behavior under overload has in tubes (English " Overdrive" ) of the amplifier special meaning: This is a condition produced in the so strong signals that the booster is no longer able to reproduce them faithfully. The result is distortion of the signal.

It can be - due to the quasi- modular design of modern tube amp (one or two series-connected " precursors " and a " final stage " ) - create different distortions. The precursors are usually with Triodensystemen ( double triodes ECC81, ECC82, ECC83 ) realized that amplifiers with Leistungspentoden ( 6L6, 6V6, EL84, EL34, and others). Overdriven is the precursor, one obtains already a distorted signal at the input of the output stage and can therefore, by down regulating the output stage, lead this distorted signal with a relatively low voltage to the speakers. This is advantageous to the low overall volume, but the sound is not the same compared with that of a distorting amplifier.

In the first tube amps from the 1950s could hardly control the precursors, but the distortion was achieved by the fact that you hired the amp as loud as possible. This means the power tubes were overridden and the transformer ( transformer for impedance matching between tubes and speakers) went into saturation, what the sound of guitarists such as Jimi Hendrix and Alvin Lee ( Ten Years After ) accounted for.

Such a signal as a curve on an oscilloscope is shown on the left. It is seen that the peaks are flattened. With increasing power, this effect is stronger.

Technically spoken messages are added to the signal in single-ended tube amplifiers increasingly even-numbered harmonics ( overtones ) and the signal is increasingly soft limits ( soft clipping ). Contrast, transistor amplifiers operate up to the maximum linear power; overdriven, the limiting ( " clipping " ) begins abruptly. Due to the approximately rectangular shape of the signal, very high frequency components (Fourier analysis) and odd due to the push-pull circuits used harmonics.

The auditory impression of distorting tube amp is described as " dense ", " loud ", " rough ", " groovy " than non- overdriven setting. This sound is important in all areas of rock music and a typical " Guitar Sound" part, for example, the music styles of Hard Rock and Heavy Metal.

Probably due to the well-intentioned override behavior and the more pronounced due to the higher internal resistance of the tube amplifier natural resonances of the loudspeaker following rule is used: Same Power Output → tube sounds twice as loud as corresponding transistor performance. However, it is to be observed that the impression of volume is to describe (loudness) is subjective, only about increasing logarithmically with increasing output power and also depends on the frequency.

A 100 watt amp is not twice as loud as a 50 watt amplifier.

Compared to 50 watts: 40 watts is 94 % as loud as 50 watts
25 watts is 81 % as loud as 50 watts
15 watts is 70 % as loud as 50 watts
5 watts is 50 % as loud as 50 watts
1 watt is 31% as loud as 50 watts

The final volume to be achieved with an amplifier is still dependent on other factors. A crucial factor is the efficiency of the speaker and the construction of the box. An increase of the efficiency by 6 dB achieved a higher sound pressure level than the doubling of amplifier power and can also significantly influenced by the change of the frequency response dynamics, and tonal character. A speaker with 10 dB higher efficiency roughly doubles the perceived loudness.

Guitar speakers typically have pronounced resonances, the speakers are hung tough and be less attenuated by the high source resistance of the tube amplifiers. In contrast, hi-fi speakers to convey the music signal as possible not have its own sound. The resonance behavior of the often open-back wooden housing is another reason for the lower attenuation and the "warm" sound with pronounced mid-shift.

The output stages of tube guitar amplifiers operate mainly in AB mode, that is, it is one tubes to amplify the positive or negative half-wave available ( push-pull). Here you will experience some crossover distortion, which does not occur when the amplifier operates in class A operation. Here, the full signal from a single power tube is reinforced. At rest flows through the tube, the half-maximum power, which is then modulated by the guitar. The AB mode is usually used for larger capacities, while the A- operation requires fewer components. In a small guitar amp can be achieved for example with an EL84 5W output power, while be achieved with two EL84 in push-pull mode, typically about 15 W. Often several tubes are connected in parallel to increase the overall performance. So powers of 100 W or more can be achieved for example with multiple EL34 parallel push-pull operation. On the other hand, there are amplifiers that combine the sound characteristics of the A - operation by parallel connection of power tubes with higher performance. A disadvantage of the A- operation is the constant, relatively high power consumption of the power tubes.

By swapping the power tube is not only the power of the amplifier, but also its sound behavior changes significantly. Often, the power tubes are not re-measured. It may also be a difference in sound occur when tubes from different manufacturers can be used. Although their nominal data are the same, but they nevertheless often produce a different sound. This is caused by manufacturing tolerances.

Examples of tube amplifiers: Marshall JCM 800 amp head 100 watts ( Box 4 x 12 ")
Mesa / Boogie Dual Rectifier 100 Watt ( Box 4 x 12 ")
Fender Twin Reverb Combo 75 Watt
Vox AC30 Combo Class AB
Orange Retro 50 Custom
Groove Tubes Soul -o Single Class A ( single-ended ), depending on the power tube 8-30 Watt
Peavey Classic

Transistor

In transistor amplifiers today are predominantly MOSFET circuits used.

Example: Marshall Lead 100 Mosfet (100 watts, reverb, name due to MOSFET power transistors, Box 4 x 10 " )
Roland Jazz Chorus JC120
Orange Crush 30R

Hybrid

Another variation is the hybrid amplifier. Since the eighties, the variant is common in the pre-amp tubes are used, while the power stage transistors is operated.

Examples: Hughes & Kettner ATS 100
Marshall Valvestate 8100 (100 watts, 3 channels, built-in reverb)

Hybrid amplifiers can but conversely also unite transistor preamp and tube power amp. This construction was popular in the seventies, when transistor output stages with the sturdiness of the best tube amps was still difficult to achieve, but allowed on the other side transistors for greater flexibility in the input and tone control stages. However, tube amps are more expensive than transistor amplifiers with the same output because of the required transformer.

Examples: Most amplifiers from Music Man (before the takeover by Ernie Ball)
Some Peavey amplifier, such as the series Mace

Simulator

The Roland simulated first successfully integrated computer models complete, acoustically detached by microphones guitar amp in various designs and companies. The company Line 6 made this method popular. In this technique, DSPs (Digital Signal Processors ) is used to simulate the behavior of tube amplifiers on mathematical models. They are also known as modeling amps.

Nowadays there are numerous guitar amplifiers that use this method of sound production. Because of the greater flexibility and range of sounds this amp more and more replace the classic guitar amps. So far, however, could modeling amps on the stage the classic tube amp is not yet fully replace. An alternative result, the company offers Tech21, which in turn umrechneten by computer in a real circuit of electronic components in order also to generate the amp computational models very real sounds.

Examples: Roland VGA -7
Hughes & Kettner zenTera
Line 6 Vetta
Fender G -DEC Family, which also offers a digital band accompaniment
VOX AD -120 VTH
Fractal Audio AxeFx

In October 2007, Line 6 and Reinhold Bogner in collaboration with the so-called Spider Valve 112/212 for the first time a modeling combo on all-tube base from which to interpret the sound of classic tube amps and high quality almost identical.

Since 2006, in his own words, a new generation of guitar amp simulators provides the U.S. Start-Up " FractalAudio " under the direction of Cliff Chase with the " AxeFx " to. For use only high quality analog -to-digital converters, and processors of high computing power. The dynamics of classic guitar amp is simulated with the help of fractal algorithms.

Manufacturer

Known manufacturers of guitar amplifiers or speakers include ( in alphabetical order):

Bass guitar Bass (sound) Chorus effect Boston (Band) Mesa/Boogie Electrical impedance Square wave Push–pull output Peavey Electronics Line 6 (company) Acoustic (John Lennon album) B.C. Rich Blackstar Amplification Gibson Guitar Corporation Laney Amplification The Selmer Company Warwick (company)

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