Construction

While guitar construction has many variations, in terms of the materials used for the body, the shape of the body, and the configuration of the neck, bridge, and pickups, there are features which are found in almost every guitar. The photo in the left side shows the different parts of an electric guitar. The headstock contains the metal machine heads, which are used for tuning ; the nut, a thin fret-like strip of metal, plastic, graphite or bone which the strings pass over as they first go onto the fingerboard; the machine heads , which are worm gears which the player turns to change the string tension and thus adjust the tuning; the frets , which are thin metal strips which stop the string at the correct pitch when a string is pressed down against the fingerboard; the truss rod , a metal cylinder used for adjusting the tension on the neck ; decorative inlay, a feature not found on lower-cost instruments.

The neck and the fretboard extend from the body; at the neck joint , the neck is either glued or bolted to the body; the body of this instrument is made of wood which is painted and lacquered, but some guitar bodies are also made of polycarbonate or other materials; pickups , which are usually magnetic pickups, but which may also be piezoelectric transducer pickups; the control knobs for the volume and tone potentiometers; a fixed bridge -on some guitars, a spring-loaded hinged bridge called a "tremolo system" is used instead, which allows players to "bend" notes or chords down in pitch or perform a vibrato embellishment; and a plastic pickguard, a feature not found on all guitars, which is used to protect the body from scratches or cover the control cavity which holds most of the electric guitar's wiring.

Pickups

Compared to an acoustic guitar, which has a hollow body, electric guitars make comparatively little audible sound simply by having their strings plucked, and so electric guitars are normally plugged into a guitar amplifier, which makes the sound louder. When an electric guitar is strummed, the movement of the strings generates (i.e., "induces") a very small electrical current in the magnetic pickups, which are magnets wrapped with coils of very fine wire. That current is then sent through a cable to a guitar amplifier. The current induced is proportional to such factors as the density of the string or the amount of movement over these pickups. That vibration is, in turn, affected by several factors, such as the composition and shape of the body.

Some "hybrid" electric-acoustic guitars are equipped with additional microphones or piezoelectric pickups (transducers) that sense mechanical vibration from the body. Because in some cases it is desirable to isolate the pickups from the vibrations of the strings, a guitar's magnetic pickups will sometimes be embedded or "potted" in epoxy or wax to prevent the pickup from having a microphonic effect.

Tremolo arms

Some electric guitars have a tremolo arm (sometimes called a "whammy bar" or "vibrato arm" and occasionally abbreviated as trem), a lever attached to the bridge which can slacken or tighten the strings temporarily, changing the pitch, thereby creating a vibrato or a portamento effect. Early vibrato systems, such as the Bigsby vibrato tailpiece, tended to be unreliable and cause the guitar to go out of tune quite easily, and also had a limited range. Later Fender designs were better, but Fender held the patent on these, so other companies used Bigsby-style vibrato for many years.
With the expiration of the Fender patent on the Stratocaster-style vibrato, various improvements on this type of internal, multi-spring vibrato system are now available. Floyd Rose introduced one of the first improvements on the vibrato system in many years when in the late 1970s he began to experiment with "locking" nuts and bridges which work to prevent the guitar from losing tuning even under the most heavy whammy bar acrobatics.

Guitar necks

Electric guitar necks can vary according to composition as well as shape. The primary metric used to describe a guitar neck is the scale, which is the overall length of the strings from the nut to the bridge. A typical Fender guitar uses a 25.5 inch scale, while Gibson uses a 24.75 inch scale in their Les Paul. While Gibson's scale has often claimed to be 24.75", it has varied through the years by as much as a half inch. The frets are placed proportionally according to the scale length; thus, the smaller the scale, the tighter the spacing of the frets.

Necks are described as bolt-on, set-in, or neck-through depending on how they are attached to the body. Set-in necks are glued to the body in the factory, and are said to have a warmer tone and greater sustain; this is the most traditional type of joint. Bolt-on necks were pioneered by Leo Fender to facilitate easy adjustment and replacement of the guitar neck. Neck-through instruments extend the neck itself to form the center of the guitar body, and are known for long sustain and for being particularly sturdy. While a set neck can be carefully unglued by a skilled luthier, and a bolt-on neck can simply be unscrewed, a neck-through design is difficult or even impossible to repair, depending on the damage. Historically, the bolt-on style has been more popular for ease of installation and adjustment; since bolt-on necks can be easily removed, there is an after-market in replacement bolt-on necks from companies such as Warmoth and Mighty Mite. Some instruments, notably most Gibson models, have continued to use set/glued necks. Neck-through bodies are somewhat more common in bass guitars.

Sound and effects

While an acoustic guitar's sound is largely dependent on the vibration of the guitar's body and the air within it, the sound of an electric guitar is largely dependent on a magnetically induced electrical signal, generated by the vibration of metal strings near sensitive pickups. The signal is then "shaped" on its path to the amplifier by using a range of effect devices or circuits that modify the tone and characteristics of the signal. The most basic sound-shaping circuitry are the volume control (potentiometer), tone control (which "rolls off" the treble frequencies), and the pick-up selectors which are found on most electric guitars, and the gain and tone (usually consisting of at least bass and treble) controls on the guitar amplifier.

A Boss distortion pedal in use

In the 1970s, as effects pedals proliferated, their sounds were combined with tube distortion at lower, more controlled volumes by using power attenuators such as Tom Scholz' Power Soak as well as re-amplified dummy loads such as Eddie Van Halen's use of a variac, power resistor, post-power-tube effects, and a final solid-state amp driving the guitar speakers. A variac is one approach to power-supply based power attenuation, to make the sound of power-tube distortion more practically available.