Bass guitars - Pickups and amplification

Pickups and amplification

For more information on pickups, see Pick up (music technology).

Magnetic pickups

Most electric bass guitars use magnetic pickups. The vibrations of the instrument's ferrous metal strings within the magnetic field of the permanent magnets in magnetic pickups produce small variations in the magnetic flux threading the coils of the pickups. This in turn produces small electrical voltages in the coils. These low-level signals are then amplified and played through a speaker. Most basses have a volume potentiometer, which can be turned up or down, and a tone potentiometer, which rolls off the high frequencies when it is turned to the player's right. Some basses may also have a pickup selector control or switch. Since the 1980s, basses are often available with battery-powered "active" electronics that boost the signal with a preamplifier, provide equalization controls to boost or cut bass and treble frequencies, or both.

P-style, split-coil pickups

• "Precision" pickups (which refers to the Fender Precision Bass), also referred to as "P pickups", are two distinct single-coil pickups. Each is offset a small amount along the length of the body so that each half is underneath two strings. The pickups are reverse-wound with reversed magnetic polarity to reduce hum. This makes the 'P' pickup a humbucking single coil pickup. Less common is the "single-coil P" pickup, used on the original 1951 Fender Precision bass. P-style pickups are generally placed in the "neck" or "middle" position, but some luthiers and performers have used P pickups in the bridge position, or in between two jazz pickups.

Dual "J"-style pickups

• "Jazz" pickups (referring to the original Fender Jazz Bass), also referred to as "J pickups", are wider eight-pole pickups that lie underneath all four strings. J pickups are typically single-coil designs, though there are a large number of humbucking designs. Traditionally, two of them are used, one of them near the bridge and another closer to the neck. As with the halves of P-pickups, the J-pickups are reverse-wound with reverse magnetic polarity. As a result, they have hum canceling properties when used at the same volume, with hum cancellation decreasing when the pickups are used at unequal volume and altogether absent when each pickup is used individually. 'J' Style pickups tend to have a lower output and a thinner sound than 'P' Style pickups. Many bassists combine a 'J' pickup at the bridge and a 'P' pickup at the neck so they can blend the two sounds.

A Yamaha BB404F, which has two passive single coil pickups

• Dual coil "humbucker" pickups, sometimes abbreviated to DC pickups, have two signal producing coils that are reverse wound around opposed polarity magnets (similar in principle to the two individual J-pickups or the two halves of a modern Precision pickup, only in a single housing). This significantly reduces noise from elecromagnetic interference compared to single coil pickups. Humbuckers also often produce a higher output level than single coil pickups, though many dual-coil pickups are marketed as retrofits for single-coil designs like the J pickup and advertise a similar output and tonal character to the stock single-coils. Dual coil pickups come in two main varieties; ceramic or ceramic and steel. Ceramic only magnets have a relatively harsher sound than their ceramic and steel counterparts, and are thus used more commonly in heavier rock styles.
  • A well-known bass humbucker is the pickup used on the Music Man series of basses; it has two coils, each with four large polepieces. This style is known as the "MM" pickup for this reason, and many aftermarket pickup manufacturers and custom builders incorporate these pickups in their designs. The most common configurations are a single pickup at the bridge, two pickups similar in placement to a Jazz Bass, or an MM pickup at the bridge with a single-coil pickup (often a "J") at the neck. These pickups can often be "tapped", meaning one of the two coils can be essentially turned off, giving a sound similar to a single-coil pickup.
• "Soapbar" Pickups are so-named due to their resemblance to a bar of soap and originally referred to the Gibson P-90 guitar pickup. The term is also used to describe any pickup with a rectangular shape (no protruding screw mounting "ears" like on P, J or MM pickups) and no visible pole pieces. Most of the pickups falling into this category are humbucking, though a few single-coil soapbar designs exist. They are commonly found in basses designed for the rock and metal genres, such as Gibson, ESP Guitars, and Schecter, however they are also found on 5- and 6-string basses made popular by jazz and fusion music, such as Yamaha's TRB and various Peavey model lines. 'Soapbar pickups' are also called 'extended housing pickups', because the rectangular shape is achieved simply by making the pickup cover longer and/or wider than it would have to be to only cover the pickup coils, and then the mounting holes are recessed inside these wider dimensions of the housing.

Many basses have just one pickup, typically a "P" or "MM" pickup, though single soapbars are not unheard of. Multiple pickups are also quite common, two of the most common configurations being two "J" pickups (as on the stock Fender Jazz), or a "P" near the neck and a "J" near the bridge (e.g., Fender Precision Bass Special, Fender Precision Bass Plus). A two-"soapbar" configuration is also very common, especially on basses by makes such as Ibanez and Yamaha. A combination of a J or other single-coil pickup at the neck and a Music Man-style humbucker in the bridge has become popular among boutique builders, giving a very bright, focused tone that is good for jazz, funk and thumbstyle.

Some basses use more unusual pickup configurations, such as a soapbar and a "P" pickup (found on some Fenders), Stu Hamm's "Urge" basses, which have a "P" pickup sandwiched between two "J" pickups, and some of Bootsy Collins' custom basses, which had as many as 5 J pickups. Another unusual pickup configuration is found on some of the custom basses that Billy Sheehan uses, in which there is one humbucker at the neck and a split-coil pickup at the middle position.

The placement of the pickup greatly affects the sound. A pickup near the neck joint emphasizes the fundamental and low-order harmonics and thus produces a deeper, bassier sound, while a pickup near the bridge emphasizes higher-order harmonics and makes a "tighter" or "sharper" sound. Usually basses with multiple pickups allow blending of the output from the pickups, with electrical and acoustical interactions between the two pickups (such as partial phase cancellations) allowing a range of tonal effects.

Non-magnetic pickups

The use of non-magnetic pickups allows bassists to use non-ferrous strings such as nylon, brass, polyurethane and silicone rubber. These materials produce different tones and, in the case of the polyurethane or silicone rubber strings, allow much shorter scale lengths.

• Piezoelectric pickups (also called "piezo" pickups) are non-magnetic pickups that use a transducer to convert vibrations in the instrument's body or bridge into an electrical signal. They are typically mounted under the bridge saddle or near the bridge and produce a different tone from magnetic pickups, often similar to that of an acoustic bass. Piezo pickups are often used in acoustic bass guitars to allow for amplification without a microphone.
• Optical pickups are another type of non-magnetic pickup. They use an infrared LED to optically track the movement of the string, similar to the mechanism of modern computer mice, which allows them to reproduce low-frequency tones at high volumes without the "hum" or excessive resonance associated with conventional magnetic pickups. Since optical pickups do not pick up high frequencies or percussive sounds well, they are commonly paired with piezoelectric pickups to fill in the missing frequencies. LightWave Systems builds basses with optical pickups.

Amplification and effects

This amplification setup is a "bass stack" approach, in which an amplifier (in this case a Hartke 5000) is plugged into separate speaker cabinets.

Like the electric guitar, the electric bass guitar is almost always connected to an amplifier and a speaker with a patch cord for live performances. Electric bassists use either a "combo" amplifier, which combines an amplifier and a speaker in a single cabinet, or an amplifier and one or more speaker cabinets (typically stacked, with the amplifier sitting on the speaker cabinets, leading to the term "half-stack" for one cabinet setups and "full stack" for two). In most genres, a "clean" bass tone (without any amplifier-induced "overdrive" or "distortion") is desirable, and so while guitarists often prefer the more desirable distorted tones of tube-transistor amplifiers, bassists commonly use solid-state amplifier circuitry to achieve the necessary high output wattages with less weight than tubes (though smaller tubes can often still be found in the low-power "preamplifier" sections of the system, where they provide a warmer, smoother character to the bass tone for relatively little additional weight). A few all-tube bass amplifiers are still available, notably from the Ampeg brand. In some cases, when the bass is used with large-scale PA amplification, it is plugged into a "DI" or direct box, which routes the signal to the bass amp while also sending the signal directly into a mixing console, and thence to the main and monitor speakers. When a recording of bass is being made, engineers may use a microphone set up in front of the amplifier's speaker cabinet for the amplified signal, a direct box signal that feeds the recording console, or a mix of both.

Various electronic bass effects such as preamplifiers, "stomp box"-style pedals and signal processors and the configuration of the amplifier and speaker can be used to alter the basic sound of the instrument. In the 1990s and early 2000s (decade), signal processors such as equalizers, overdrive devices (sometimes referred to as "fuzz bass"), and compressors or limiters became increasingly popular. Modulation effects like chorus, flanging, phase shifting, and time effects such as delay and looping are less commonly used with bass than with electric guitar, but they are used in some styles of music.