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Online-Guide Guitar Amp Heads
Valve Amp Basics

 

Amplifier circuits can be described in terms of the layout or ‘topology’ of components which plays a crucial part in shaping the sound. Most classic guitar amps employ the ‘Class A’ design, which is characterised by wide dynamic range, penetrating tone and creamy
DistortionIn most cases distortion is an undesirable alteration to a signal which occurs when a piece of equipment is driven with a input level that is too high for its operating level. Sometimes, as in the case of guitar distortion, this can be an intentional and desirable effect.
distortion
. Early Class A designs without a
Master1) The final version of an audio recording or album that has been prepared for release. 2) The physical medium on which this recording is stored or transferred, such as a glass master CD, CDR or vinyl master from which a production run will be replicated or pressed.
master
Volume1) In audio and music, the loudness or amplitude of a signal. 2) In computing, a fixed amount of storage space, addressed as a single entity ('C:', 'D:' etc). A physical drive may contain more than one volume, but a single volume may also span more than one drive!
volume
control could of course only produce their
DistortionIn most cases distortion is an undesirable alteration to a signal which occurs when a piece of equipment is driven with a input level that is too high for its operating level. Sometimes, as in the case of guitar distortion, this can be an intentional and desirable effect.
distortion
at full
Volume1) In audio and music, the loudness or amplitude of a signal. 2) In computing, a fixed amount of storage space, addressed as a single entity ('C:', 'D:' etc). A physical drive may contain more than one volume, but a single volume may also span more than one drive!
volume
, and so one of the disadvantages of this design is that the valves are subject to relatively high wear and tear – regular maintenance is therefore essential.

Class B designs are much less subject to wear, and also maintain a cleaner signal through most of the path - they are ultimately more flexible.

Mesa-Boogie
ValveA device consisting of a glass tube from which air is removed, containing one or more electrical contacts operating at high temperature, which as the predecessor of the transistor, was essential to the development of electronics (particularly amplification) and is still favoured in guitar amplification and high-end hi-fi for its warm sound.
valve
amps, regarded as among the most advanced modern designs, combine the best of Class A and B circuitry in various ways, which are often user-switchable for maximum flexibility.

construction

Other than their topology,
ValveA device consisting of a glass tube from which air is removed, containing one or more electrical contacts operating at high temperature, which as the predecessor of the transistor, was essential to the development of electronics (particularly amplification) and is still favoured in guitar amplification and high-end hi-fi for its warm sound.
valve
amps are also commonly characterised as having either a ‘British’ or ‘American’ sound. The difference applies mainly to the overdriven sound and can be hard to describe in words, but broadly speaking, ‘British’ generally refers to the classic rock sounds of the seventies (Led Zeppelin, Deep Purple, Free, Thin Lizzy etc), whereas the American sound has found favour with bands such as Green Day.

Modern heads and combos generally have a similar array of features. Most have two separate channels – essentially separate
PreampAn amplifier device or circuit that provides initial amplification of a weak electronic signal, usually to 'line' level, in order for it to be processed or passed between other devices, as opposed to a power amp which amplifies a signal in order to drive loudspeakers. Examples include microphone preamps (as dedicated hardware and in mixing desks/recording interfaces) and guitar preamps. Most guitar amps combine the preamp and power amp in the same unit.
preamps
– which are optimised for clean and
DistortionIn most cases distortion is an undesirable alteration to a signal which occurs when a piece of equipment is driven with a input level that is too high for its operating level. Sometimes, as in the case of guitar distortion, this can be an intentional and desirable effect.
distortion
sounds respectively, and selectable via
FootswitchA switch operated by the foot to turn on or off a function while both hands are playing an instrument as in guitar effects pedals or synthesizer patch changing.
footswitch
. Some manufacturers such as Mesa-Boogie have added a third ‘crunch’ channel for overdriven rhythm playing.

Most amps incorporate an
EffectsGeneral term applied to audio processors for dynamics, time, ambience and equalisation whether in the form of 19" rack units, guitar floor pedals, or software plug-ins.
effects
(‘FX’) loop enabling the connection of external
EffectsGeneral term applied to audio processors for dynamics, time, ambience and equalisation whether in the form of 19" rack units, guitar floor pedals, or software plug-ins.
effects
such as
Chorus1) A delay-based effect that simulates the sound of a group of the same instruments. Regarded as a soft modulation, effect it can create rich textures through phasing and mixing of layers. 2) The part of a song that acts as a recurring theme or refrain.
chorus
,
DelayAn outboard unit used to create time dependent effects where a source signal is sampled/recorded and replayed later by a adjustable amount, either singly or in multiples. The amount of delay results in a range of effects from chorus and slap back to rhythmic echo. Also used for time correction in large PA systems.
delay
and phasing. This is usually placed between the
PreampAn amplifier device or circuit that provides initial amplification of a weak electronic signal, usually to 'line' level, in order for it to be processed or passed between other devices, as opposed to a power amp which amplifies a signal in order to drive loudspeakers. Examples include microphone preamps (as dedicated hardware and in mixing desks/recording interfaces) and guitar preamps. Most guitar amps combine the preamp and power amp in the same unit.
preamp
and power
AmpereUnit of current; the amount of electricity flowing through a conductor. One Ampere is equal to the flow of 6.25x10^18 electrons through a conductor in one second.
amp
, although some amps include flexible
RoutingThe method of passing signals from a source to a destination for mixing or processing, either via an audio console's internal busses using routing switche, or with a patchbay using patch cables.
routing
options, for example allowing the FX loop to be assigned to one channel but not the other. An FX loop is particularly important if you like the amp’s own
DistortionIn most cases distortion is an undesirable alteration to a signal which occurs when a piece of equipment is driven with a input level that is too high for its operating level. Sometimes, as in the case of guitar distortion, this can be an intentional and desirable effect.
distortion
, as opposed to using a
DistortionIn most cases distortion is an undesirable alteration to a signal which occurs when a piece of equipment is driven with a input level that is too high for its operating level. Sometimes, as in the case of guitar distortion, this can be an intentional and desirable effect.
distortion
pedal, but want to add a
ModulationThe varying of some property of a waveform, usually in response to another signal. For example, in amplitude modulation (AM), one signal is used to vary the amplitude of another; in frequency modulation (FM), one signal varies the frequency of the other.
modulation
effect such as
Chorus1) A delay-based effect that simulates the sound of a group of the same instruments. Regarded as a soft modulation, effect it can create rich textures through phasing and mixing of layers. 2) The part of a song that acts as a recurring theme or refrain.
chorus
, which must be added after
DistortionIn most cases distortion is an undesirable alteration to a signal which occurs when a piece of equipment is driven with a input level that is too high for its operating level. Sometimes, as in the case of guitar distortion, this can be an intentional and desirable effect.
distortion
Chorus1) A delay-based effect that simulates the sound of a group of the same instruments. Regarded as a soft modulation, effect it can create rich textures through phasing and mixing of layers. 2) The part of a song that acts as a recurring theme or refrain.
chorus
before
DistortionIn most cases distortion is an undesirable alteration to a signal which occurs when a piece of equipment is driven with a input level that is too high for its operating level. Sometimes, as in the case of guitar distortion, this can be an intentional and desirable effect.
distortion
sounds rather unpleasant! Other
EffectsGeneral term applied to audio processors for dynamics, time, ambience and equalisation whether in the form of 19" rack units, guitar floor pedals, or software plug-ins.
effects
such as
DelayAn outboard unit used to create time dependent effects where a source signal is sampled/recorded and replayed later by a adjustable amount, either singly or in multiples. The amount of delay results in a range of effects from chorus and slap back to rhythmic echo. Also used for time correction in large PA systems.
delay
and wah-wah can be used in either configuration according to taste.

Amps’ power ratings give only a very rough indication of maximum
Volume1) In audio and music, the loudness or amplitude of a signal. 2) In computing, a fixed amount of storage space, addressed as a single entity ('C:', 'D:' etc). A physical drive may contain more than one volume, but a single volume may also span more than one drive!
volume
, particularly as much depends on the
ImpedanceThe term for electrical resistance when applied to AC current.
impedance
, configuration and
SensitivityThe input level (in dB) required by an audio device to drive it to its rated output level.
sensitivity
of the speaker(s) they’re connected to. As a general indication though, many loud combos are rated at 50 or 60 Watts, and heads rated at 100W have a little more power for comfortably driving four or even eight speakers.

Lastly, guitar speaker connections are usually made with quarter-inch
JackA connector used for audio input/output on many devices including sound modules, mixing desks and guitars. Usually found in 6.4mm and 3.5mm varieties, either mono, or stereo/balanced/TRS (Tip Ring Sleeve).
jack
leads. Although speaker leads have exactly the same external appearance as ordinary
JackA connector used for audio input/output on many devices including sound modules, mixing desks and guitars. Usually found in 6.4mm and 3.5mm varieties, either mono, or stereo/balanced/TRS (Tip Ring Sleeve).
jack
leads, they should never be mixed up. Instrument/line level cable is co-axial in design - a single core is surrounded by a braided shield which protects the signal from interference. The thin wire used results in a high
ImpedanceThe term for electrical resistance when applied to AC current.
impedance
, which at best will degrade the signal between
AmpereUnit of current; the amount of electricity flowing through a conductor. One Ampere is equal to the flow of 6.25x10^18 electrons through a conductor in one second.
amp
and speaker, and at worst can overheat to the point of catching fire! On the other hand, speaker cable consists of two cores and no shield - using a lead made from this between guitar and
AmpereUnit of current; the amount of electricity flowing through a conductor. One Ampere is equal to the flow of 6.25x10^18 electrons through a conductor in one second.
amp
, while not dangerous, will usually be very noisy.

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