The electric bass guitar, sometimes "electric bass" or simply "bass" in common conversation, is an instrument developed in the 1950s from elements of the upright bass and the electric guitar. The intent was to create an easily-amplified bass string instrument that could be learned easily by guitar players, and heard over the drum kits and brass sections popular in jazz and blues groups of the day. While Audiovox claims credit for the first fretted electric bass, the first mass-produced bass guitar was the Fender Precision Bass, made popular by Monk Montgomery, bassist for Lionel Hampton, as well as other bassists for famous touring acts such as Bill Black (Elvis Presley) and James Jamerson (The Funk Brothers). The instrument caught on in popular music genres, and new designs were introduced, such as the Fender "Deluxe Bass" which would evolve into the "Jazz Bass", Gibson's offerings such as the EB-3 based on their popular SG body style, and the Rickenbacker 4000 series, the first bass to feature a "neck through" construction as opposed to "set-neck" or "bolt-on" constructions favored by Gibson and Fender. In these various incarnations, the electric bass has all but replaced the upright acoustic bass in most genres, with the upright remaining popular mainly in country-western and Latin styles.

The typical bass guitar is a solid-body instrument, styled similarly to but larger than a solid-body electric guitar such as a Stratocaster, with four strings tuned to E, A, D and G, similar to an upright bass and one octave lower than the lower four strings of an electric guitar. More recently, basses with five and six strings, adding a low B and a high C respectively, have become popular in most genres as the extended range avoids the need to "detune" a four-string bass, common in classic rock and metal genres. The typical "scale length" of an electric bass ranges between 30" and 36", with the standard "long scale" for most instruments being 34".

The Precision Bass had only one magnetic pickup, originally a single-coil similar in design to a Telecaster bridge pickup, but evolving to a "split-coil" design allowing hum-cancelling operation. Most basses nowadays have two pickups, at the "neck" and "bridge" positions, of varying types, ranging from classically-styled "P" (Precision) and "J" (Jazz) pickups to more modern "MM" (Music Man) and "soapbar" pickup shapes, all with subtly different tonal palettes. Similar to guitars, some of these pickups are "single coil", offering a brighter, fuller tone with more detail at the cost of picking up and amplifying background electronic noise such as from fluorescent lights. Others are "humbucking" or "hum-cancelling", employing two coils in a single pickup that have the polepieces arranged with reverse polarity, and the wire coil wrapped in opposite directions; the result is that the actual signal from the string moving across the pickup's magnetic field is "in phase" between the two coils, but electromagnetic noise picked up by both coils ends up "out of phase" and cancels out. Humbuckers typically have a stronger signal than single coils due to the extra coil, but the same in-phase/out-of-phase design that rejects EMI can also cause the pickup to lose some subtleties of tone produced by the vibrating string, especially in the higher harmonics.

Unlike in guitars, where electronics for most classic styles have remained "passive" (relying solely on the natural induction caused by the string moving over the magnet and pickup coil to produce the signal), a significant portion of basses available today have "active" electronics, with a preamplifier powered by a battery to provide more flexible tone-shaping capability (and higher gain) than a passive tone circuit. Active electronics can be used with any pickup, but are required for certain types of pickups that produce a lower-strength signal or that require lower impedance (AC resistance) to operate properly. Examples of such pickups include piezoelectric pickups or "piezos", lower-impedance "active" magnetic pickups, optical sensors, and other designs. These pickups are similarly seen more often in basses than on guitars, though piezo pickups are commonly seen in acoustic guitars, where the pickup is prized for its natural sound incorporating both the vibrations of the string and the body of the guitar, and the resulting ability for the guitar to be amplified without requiring a microphone in front of it (useful in live performance situations where the performer wants to move around stage).

While amplifier circuits based on older vacuum-tube diodes and transistors are commonly prized by bassists as well as guitarists for the warmth and character of the resulting tone, the sheer wattage needed to cleanly amplify bass to desired on-stage volumes typically precludes using tube-based "power amplifiers" to drive the speakers. While 100 watts typically represents the upper end of power ratings in guitar amplification, differences in human perception of bass frequencies, as well as the need for the bass to be heard over multiple guitar amplifiers and a drumkit, require most on-stage bass amplifiers to be rated for much higher wattages, up to 1000W (beyond that, bassists usually rely on the house's own PA system for additional amplification). High-end amplification systems for bass therefore typically uses a tube-based preamplifier circuit, giving a good measure of vintage-style tube tone, coupled with a solid-state power amplifier, typically combined into a single "amp head". All-solid-state circuitry is also common, especially at lower power ratings and pricepoints, and offers good sound quality and volume for practice and for smaller venues without the cost and weight of tubes.

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