Bass amplifier

From Wikipedia, the free encyclopedia
  (Redirected from Bass instrument amplification)
Jump to: navigation, search
An Ampeg SVT cabinet with eight 10" speakers, with a separate amplifier "head".
A Yamaha B100-115 combo amp, which contains a 100 watt amplifier and one 15" speaker in a wooden cabinet.

A bass amplifier or "bass amp" is a musical instrument amplifier that accommodates the requirements of lower-pitched instruments such as the bass guitar or double bass. Bass amps typically consist of a preamplifier, tone controls, a power amplifier and one or more loudspeakers in a wooden cabinet. While bass amps share many features with the guitar amplifiers used for electric guitar, such as providing tone and volume controls and a carrying handle, they are distinct from other types of amplification systems, due to the particular challenges associated with low-frequency sound reproduction. This distinction affects the design of the loudspeakers, the size and design of the speaker cabinet and the design of the preamplifier and amplifier. Speaker cabinets for bass amps usually incorporate larger loudspeakers (e.g., 15" speakers are more common for bass than for electric guitar amps) or more speakers than those used for the amplification of other instruments. The loudspeakers themselves must also be sturdier to handle the higher power levels and they must be capable of reproducing very low pitches at high sound pressure levels.

Bass amp speaker cabinets are typically more rigidly constructed and heavily braced than those for non-bass instrument amplification. They usually include tuned bass reflex ports or vents cut into the cabinet, for increased efficiency at low frequencies. Preamplifier sections have equalization controls that are designed for the deeper frequency range of bass instruments, which extend down to 40 Hz or below. Bass instrument amplifiers are more likely to be designed with cooling fans than regular guitar amplifiers, due to the high power demands of bass instrument amplification. They are also more commonly equipped with audio compression or limiter circuitry to prevent overloading the power amplifier and to protect the speakers from damage due to unintended clipping in the power amp.

A common format of bass amplifier–the "combo" amp–contains the amplifier electronics and one or more speakers in a single wooden cabinet. Combo amps are widely used for rehearsals and for performances at small to mid-size venues. For larger venues, such as stadiums, bassists may use the "bass stack" approach, in which one or more separate speaker cabinets, each with one or more speakers (but not containing an amplifier) and a separate "head" containing the amplifier electronics are used. With a large "bass stack", a bassist can obtain a much higher wattage and onstage volume than a "combo" amp could provide. As with an electric guitar amp, a bass amp is not simply used to make the instrument louder; performers use the preamplifier and equalizer controls and, in amps from the 1980s onward, the onboard electronic effects, to create their preferred tone.

History[edit]

1950s–1970s[edit]

A vintage Ampeg B-15 amp and speaker cabinet.

The Ampeg Bassamp Company, founded in 1949 by Everett Hull, produced bass amplifiers that were widely used by electric bass guitarists in the 1950s and 1960s. The first bass amplifier offered by Ampeg was an 18-watt model with a single 12" speaker and a rear ventilation port called the Super 800. In 1951, they introduced a 20-watt version with a 15-inch speaker. In 1960, they introduced the B-15 Portaflex, a flip-top 25-watt bass amplifier with a single 15" speaker. In the late 1960s, the 300-watt Super Vacuum Tube (SVT) amplifier head, which was intended for large performance venues. The SVT was intended for use with one or two speaker cabinets containing eight 10" speakers.

When the Fender company invented the first widely produced electric bass guitar (the Fender Precision Bass) they also developed a bass amplifier, the Fender Bassman, first produced in 1952. This was a 26-watt tube amplifier with a single 15" speaker. In 1954, the Bassman was redesigned to use four 10" speakers. This speaker cabinet was an open-back design; as such, it had poor low-frequency efficiency and was prone to blowing speakers when used for bass because of the lack of damping. Somewhat ironically, it became very popular as a guitar amplifier. The circuit design also underwent repeated modifications. The "5F6A" circuit introduced in 1958 is regarded as a classic amplifier design and was copied by many other manufacturers, such as Marshall.

A Kustom 200 bass amplifier from 1971, featuring a separate amp head on top of a 2 x 15" speaker cabinet.

The early rock bands of the 1960s used the PA system only for vocals. The electric guitarist and electric bassist had to produce their sound for the hall or other venue with their own amplifiers. As a result, bass players from the 1960s often used large, powerful amplifiers and large speaker cabinets. Some bass players would even use multiple bass amplifiers, with the signal from one bass amp being sent to one or more "slave" amps.

In the mid-1960s John Entwistle, the bassist for The Who, was one of the first major players to make use of Marshall stacks. At a time when most bands used 50 to 100-watt amplifiers with single cabinets, Entwistle used twin stacks with new experimental prototype 200-watt amplifiers. This, in turn, also had a strong influence on the band's contemporaries at the time, with Jack Bruce of Cream and Noel Redding of the Jimi Hendrix Experience both following suit. Entwistle also experimented throughout his career with "bi-amplification," where the higher frequencies of the bass sound are divided from the lower frequencies, with each frequency range sent to separate amplifiers and speakers. This allows for more control over the tone, because each portion of the frequency range can then be modified (e.g., in terms of tone, added overdrive, etc.) individually. The Versatone Pan-O-Flex amplifier used a different approach to bi-amplification, with separate amplifier sections for bass and treble but a single 12-inch speaker. The Versatone was used by well-known bassists such as Jack Casady and Carol Kaye.

1980s–2010s[edit]

A bass rack from a professional bass player's touring setup. The bass amplifier is the lowest chassis in the rack; above it are a wireless receiver, several pre-amp devices, and a power conditioner.

As PA systems improved, horn-loaded "bass bins" and subwoofers were added and were often well-equipped to amplify directly-fed bass guitar and keyboard frequencies. As well, in the 1980s and 1990s, monitor systems were substantially improved, which allowed sound engineers to provide on-stage musicians with a loud, clear, and full-range reproduction of their instruments' sound.

In this 2007 photo of The Police's singer-bassist Sting, several Ampeg cabinets with multiple 10" speakers can be seen on the left side.

As a result of the improvements to PA systems and monitor systems, bass players in the 2000s no longer need to have huge, powerful amplifier systems to play stadiums and arenas. Instead, contemporary bass amplifiers usually have DI output jacks that can be patched to the PA. In the 2000s, virtually all of the sound reaching the audience in large venues comes from the PA system. As well, in the 2000s on-stage instrument amplifiers are more likely to be kept at a low volume, because high volume levels on stage makes it harder to control the sound mix and produce a clean sound. As a result, in many large venues much of the on-stage sound reaching the musicians now comes from the monitor speakers, not from the instrument amplifiers. Stacks of huge speaker cabinets and amplifiers are still used in concerts in some genres of music, especially heavy metal, but they tend to be used more for the visual effect than for sound reproduction.

In some small to mid-size venues, such as bars and nightclubs, the PA system may not have the capacity to provide the bass sound for the venue, and the PA system may be used mainly for vocals. Bass players in bands that play at a variety of venues, including these types of small to mid-size venues, may need to be able to provide the bass sound for the venue, and so they will require a large combo amp or bass stack with this capability.

Types[edit]

Different types of equipment are used to amplify the electric bass and other bass instruments, depending on the performance setting, style of music, the sound desired by the bassist and other factors, such as whether a bassist is an amateur or professional musician. Professional bassists are more likely to have expensive "boutique" amps and cabinets. All types of bass amps and cabinets are designed to be transportable to shows and recording studios, and as such, most have various features to protect the cabinet (e.g., metal or plastic corner protectors) and speakers (a plastic screen or metal grille) during transportation and move the equipment (a single carry handle is standard for practice amps and combo amps and two handles are sometimes provided for two-handed carrying of large cabinets, and wheels are mounted on some large combo amps and cabinet). Amplifier "heads" may be sold mounted in a wooden cabinet with a carrying handle, or they may be sold as rackmount-able components, which can be screw-mounted in a 19" road case for protection.

Practice amps[edit]

The small practice amplifier has low wattage and low volume which make it mostly suited to individual practice.

The smallest bass amps, which typically have 10 to 15 watts of power and a small 8" speaker, are known as practice amps. They amplify the instrument enough for individual practice. Practice amps do not produce enough volume or low-frequency sound reproduction to be used in a band rehearsal or show. They may have an open-back design, like an electric guitar combo amp; most bass combo amps and speaker cabs are closed-back (often with bass reflex ports or vents). Some buskers playing on the street for tips may use battery-powered practice amps, a feature available on some models. A device similar in function to a practice amp is a headphone amp. It amplifies the signal from an electric bass so that a bassist can hear the instrument with headphones. Headphone amps can be used for pre-show warm-up or silent practice in a hotel room or apartment where the use of a bass amp could create a noise disturbance.

Combo amps[edit]

For rehearsals, studio recording sessions, or small club performances, electric and upright bass players typically use a "combo" amplifier, which combines a preamplifier, tone controls, a power amplifier and a speaker (or multiple speakers) in a single cabinet. Combo amps come in a variety of speaker configurations, such as one speaker (e.g., often one 12" speaker or one 15" speaker, although there are some micro-amps with one 10" speaker) or two speakers (e.g., two 10" speakers) or four speakers (e.g., four 10" speakers). The most powerful combo amps available deliver around 800 watts to the internal speakers. Smaller combo amps may be easier to transport and set up than using separate amplifier and speaker units, and as such, they are a popular choice for many bass players. Bass players in quieter, more acoustic genres (e.g., jazz quartets which play in a wine bar or a folk music group which plays in a coffeehouse) may be able to use smaller, more modestly powered combo amps. Bassists who play in genres more associated with a high stage volume (e.g., hard rock or electric blues) may tend to use, larger, more powerful combo amps.

Bass stacks[edit]

Psychobilly bassist Jimbo Wallace onstage with Reverend Horton Heat; note his large bass stack consisting of a 1x15" cabinet, a 4x10" cabinet, and an amplifier "head".

For larger venues such as large clubs and outdoor music festivals, or for music genres that use bass instruments with an extended lower range and high stage volumes (e.g., heavy metal music), bass players often use a more powerful amplifier (300 to 1000 watts or more) and separate speaker cabinets (often called "cabs") in various combinations. Using a separate amplifier cabinet and speaker cabinets is colloquially referred to as a "bass stack".

Speaker cabinets[edit]

A selection of bass cabinets. From left to right: a Fender cab, a Genz Benz cab (and amp head) and two Aguilar cabinets.

A bass stack may use a single speaker cabinet (e.g., the huge 8x10" cabinets widely used by hard rock and metal bassists). Other large single cabinets are less commonly used, such as the 6x8" and 8x8" cab configurations. Users of two cabinets may use two 4x10" cabinets (more easy to transport than a single 8x10" cab), a 15" cab and a 2x10" cab, or other variations (e.g., a 2x15" cab and a 4x10" cab). Some metal bassists, such the bass player for death metal band Cannibal Corpse use two 8x10" cabinets for large concerts.

One reason that some bass players choose to use a "bass stack" rather than a combo is that the separate component approach enables bassists to use different speaker cabinets for different shows or activities. For example, a bassist playing a stadium may use an 8x10" cab for this show, but then bring a 4x10" cab for a nightclub show the next day, or a 1x12" cab for a studio recording.

Large speaker cabinets such as 8x10" enclosures may have wheels and a "towel bar" to facilitate transportation. Speaker cabinets with 1/4 input jacks typically have two parallel jacks, so that the amp head may be plugged into one cabinet, and then a second cabinet can be "daisy chained" by connecting it to the first cabinet. Cabinets with horn-loaded tweeters often have an attenuator knob for controlling the tweeter. Some 2000s-era speaker cabinets may have Speakon jacks.

Heads[edit]

A Hartke LH500 bass amplifier "head", which is rated at 500 watts.
A MesaBoogie bass amplifier "head"; note the graphic equalizer sliders on the right side

Separate bass amplifiers, often called 'heads' or 'amp heads' are usually integrated units, with a preamplifier and power amplifier combined in a single unit. Some players use separate preamplifier/power amplifier setups, where one or more preamplifiers drive one or more power amplifiers. These preamps and power amps and any effect units, such as an audio compressor, are typically mounted in 19" rack mount road cases for safe transport.

Another reason that some bassists prefer the "bass stack" approach is that it is much easier to customize a separate preamp/amp/speaker cabinet setup with a bass stack than it is to customize a combo amp. With a bass stack setup, a professional bassist can handpick the brands of preamplifier, graphic equalizer, power amplifier and speaker cabinet(s) they wish to use. It is also much easier to replace defective components with a bass stack than with a combo amp. If the power amp on a combo amp fails, only an electronics technician can repair or replace the power amp. With a bass stack, in which the power amp may be a separate component in a rackmount road case, the defective power amp can be removed with only a screwdriver and a new power amp can be mounted in the rack and connected to the other components. This facilitates replacement of components while on tour.

Amplifier technology[edit]

Amplifiers may be based on thermionic ("tube" or "valve") or solid state (transistor) technology.

Tube amplification[edit]

A close-up of a vacuum tube from a Fender Bassman bass amp.

Vacuum tubes were the dominant active electronic components in bass amplifiers manufactured until the early 1970s, and tubes continue to be used for higher-end units. Tube amplifiers for bass almost always use class AB1 topology for efficiency reasons. Many bass players believe that tube amplifiers produce a "warmer" or more "natural" sound than solid state amplifiers when lightly or moderately driven, and more pleasing distortion characteristics when overdriven. Some also believe that they have a greater level of perceived loudness for a given amount of amplifier power. Even though tube amplifiers produce more heat than solid state amplifiers, few manufacturers of tube amplifiers include cooling fans in the amplifiers' chassis. Usually adequate cooling is provided by passive convection. Adequate airflow is needed to prevent excessive heat from shortening the tubes' lifespan or producing tonal inconsistencies.[1]

Solid state amplification[edit]

By the 1960s and 1970s, semiconductor transistor-based amplifiers began to become popular. This was in large part because solid state amplifiers are less expensive, lighter weight, and require less maintenance than tube amplifiers. In some cases, tube and solid state technologies are used together, usually with a tube preamplifier driving a solid state power amplifier. There are also an increasing range of products that use digital signal processing and digital modeling technology to simulate many different combinations of amp and cabinets.

The output transistors of solid state amplifiers can be passively cooled by using metal fins called heat sinks to radiate away the heat. For high-wattage amplifiers, a fan is often used to move air across internal heatsinks.[2] Since transistor bass amplifiers used for large venues need to produce a high output, this usually means that bass amplifiers are very heavy. Most powerful transistorized bass amplifiers use class AB or so-called "push-pull" topology. These need heavy transformers and require large metal heat sinks for cooling. However, Class D amplifiers (also called "switching amplifiers") are more efficient than conventional Class-AB amplifiers, and so are lighter in weight and smaller. The Acoustic Image Focus head, for example, produces 800 watts of power and weighs 2.2 kilograms (about 4 pounds). Class-D amplifiers use MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) rather than 'ordinary' (bipolar) transistors, and generate a pulse-width modulated signal that is filtered before it reaches the speaker.[3]

Power and volume[edit]

The relationship between perceived volume and power output in watts of a bass amp is not immediately obvious. While beginners sometimes assume that there is a linear relationship between perceived volume and wattage (e.g., they assume that a 50-watt amp will be much louder at than a 5-watt amp), in fact the human ear perceives a 50-watt amplifier as about twice as loud as a 5-watt amplifier (which is a tenfold increase in power in watts). A 50-watt amplifier is heard as a quarter louder than a 0.5-watt amp. Doubling the power of an amplifier results in a "just noticeable" increase in volume, so a 100-watt amplifier is only just noticeably louder than a 50-watt amplifier. Such generalizations are also subject to the human ear's tendency to behave as a natural compressor at high volumes. As such, if a bassist is finding that their 50 watt amp is not loud enough to be heard in the band being played in, and if they believe they need to have an amp that produces twice the volume, they should test various 500 watt amps. A 100 watt amp will be only slightly louder than the original 50 watt amp.

Bass players need more wattage in their amplifiers to get a clean, undistorted sound that is loud enough onstage in a rock group where drums and electric guitar are used; a bass player will typically need three or four times the wattage of the electric guitarist, as bass frequencies require more power to reproduce.[4] For example, if an electric guitarist has a 100 watt amp, the bassist in the band should have a 300 to 400 watt bass amp. A tube bass amp will sound louder than a solid state bass amp of the same wattage.[5]

Loudspeakers[edit]

Music store display showing a variety of bass "combo" amplifiers and speaker cabinets.

The lowest note on the double bass or four-stringed electric bass is E1, two octaves below middle C (approximately 41 Hz), and on a five-string it is B0 (approximately 31 Hz).[6] The requirement to reproduce low frequencies at high sound pressure levels means that most loudspeakers used for bass guitar amplification are designed around large diameter, heavy-duty drivers, with 10", 12" and 15" being most common.

In some genres, bass players use a large number of speaker cabinets for a powerful onstage sound.

Bassists who want powerful low end may use a subwoofer cabinet designed for a PA system. Subwoofers can only produce frequencies up to about 150 or 200 Hz, so a subwoofer cabinet must be paired with a full range speaker to obtain the full tonal range of an electric bass or upright bass. Bass guitar players who may use subwoofer cabinets include performers who play with extended range basses with include notes between B0 (about 31 Hz); and C#0 (17 Hz); bassists who play in styles where a very powerful sub-bass response is an important part of the sound (e.g., funk, Latin, gospel, R & B, etc.).

Keyboard players who use subwoofers for on-stage monitoring include electric organ players who use bass pedal keyboards (which go down to a low "C" which is about 33 Hz) and synth bass players who play rumbling sub-bass parts that go as low as 18 Hz. Of all of the keyboard instruments that are amplified onstage, synthesizers can produce some of the lowest pitches, because unlike a traditional electric piano or electric organ, which have as their lowest notes a low "A" and a low "C", respectively, a synth does not have a fixed lowest octave. A synth player can add lower octaves to a patch by pressing an "octave down" button, which can produce pitches that are at the limits of human hearing.

Several concert sound subwoofer manufacturers suggest that their subs can be used for bass instrument amplification. Meyer Sound suggests that its 650-R2 Concert Series Subwoofer, a 14-square-foot (1.3 m2) enclosure with two 18-inch drivers, can be used for bass instrument amplification.[7] While performers who use concert sound subwoofers for onstage monitoring may like the powerful sub-bass sound that they get onstage, sound engineers may find the use of large subwoofers (e.g., two 18" drivers) for onstage instrument monitoring to be problematic, because it may interfere with the "Front of House" sub-bass sound.

Cabinet design[edit]

Main article: Loudspeaker enclosure
Bass reflex speaker enclosures, which have a vent or port cut into the cabinet, are widely used for bass amp cabinets.

Most bass speaker cabinets employ a vented bass-reflex design, which use a port or vent. Others use acoustic suspension designs with sealed cabinets; these are relatively uncommon because they are less efficient. Some cabinets use a transmission-line design similar to bass-reflex, and some large cabinets use horn-loading of the woofers.

It is typically not possible to combine high efficiency (especially at low frequencies) with compact enclosure size and adequate low frequency response. Bass cabinet designers can, for the most part, choose only two of the three parameters when designing a speaker system. So, for example, if extended low-frequency performance and small cabinet size are important, one must accept low efficiency.[8] This rule of thumb is sometimes called Hofmann's Iron Law (after J.A. Hofmann, the "H" in KLH).[9][10]

Tweeters[edit]

A 150-watt "combo" bass amp with a horn-loaded tweeter (in the top right of the speaker cabinet).

High frequency tweeters, typically horn-loaded, are included in some bass instrument speaker cabinets. Vox's 1960s-era "Super Beatle" amplifier was an early enclosure that used horn tweeters. During the late 1960s Acoustic's 260 Series guitar amp used a treble horn in the dual 15" 261 guitar enclosure, and Kustom's nearly 5-foot-tall (1.5 m) 2J + 1H guitar enclosure used two 15" speakers and a 15" diameter treble horn. Horn-equipped cabinets were not available for bass players until much later.

In the early 1980s, some performers began using two-way or three-way cabinets that used 15" woofers, a vented midrange driver and a horn/driver, with an audio crossover directing the signal to the appropriate driver. Folded horn bass guitar rigs have remained rare due to their size and weight. As well, since the 1990s, most clubs have PA systems with subwoofers that can handle the low range of the bass guitar. Extended range designs with tweeters were more the exception than the rule until the 1990s. The more common use of tweeters in traditional bass guitar amplifiers in the 1990s helped bassists to use effects and perform more soloistic playing styles, which emphasize the higher range of the instrument.

One problem with adding a tweeter to a bass speaker cabinet is that the tweeter may be damaged by the overdriven amplifier tone that is popular in some musical genres, since overdriving the amplifier adds a great deal of high frequency information to the signal. Horns and speakers in the same cabinet are sometimes wired separately, so that they can be driven by separate amplifiers. Biamplified systems and separately-wired cabinets produced by manufacturers such as Gallien-Krueger and Carvin and other manufacturers allow bassists to send an overdriven sound to the speaker, and a crisp high sound to the horn, which prevents this problem.

Controls, jacks and indicator LEDs[edit]

Controls[edit]

The controls for a rackmount bass amp "head", the Hevos400D.

There are two main types of controls on bass amps: switches and rotary knobs. The simplest, least expensive practice amps and combo amps may only have a few switches and knobs, such as an "on/off" switch, a volume knob, and a bass and treble control. Mid-range models may add additional tone controls (e.g., one or two "midrange" controls) and/or add a second type of volume knob called a "gain" or "preamplifier" control. On some amps, setting the "gain" or "drive" control above a certain setting causes an overdrive effect, either due to the natural effect of overdriving the preamplifier and/or due to a distortion effect being turned on. Tube amplifiers typically also have a "standby" switch in addition to an "on/off" switch. Controls are typically mounted on the front of the amplifier near the top of the cabinet; often the knobs are recessed so that they do not project beyond the wooden cabinet, to protect the knobs during transportation. On amplifier "heads", protective metal U-shaped protrusions may be used to protect the knobs. On some amps, notably Roland models, the knobs and switches may be on top of the amplifier, at the rear of the top surface. Again, the knobs are usually recessed below the top of the wooden cabinet.

Mid-to high-range amps may have other switches (which on some amps are switched on by pulling an existing rotary knob out) that boost or cut some part of the frequency range, such as "bright boost", "deep boost" or "mid scoop" switches. Amps with an onboard audio compressor or limiter, which is used to protect the speakers, may have only an on/off switch to turn on the effect, or they may have one or more knobs to control how much compression is applied to the bass tone. Some 2000s-era amps may have an electronic tuner and a mute button, to mute the sound of tuning during a break between songs without having to change the volume settings. On some amps, vertical sliders may be provided to control a graphic equalizer. Higher-end amps with a DI out jack may also have a "ground lift" switch (to be used in case of a humming ground loop) and/or a switch which determines whether the DI out signal to the PA or recording mixing board is pre- or post- the amp's internal preamplifier and equalization circuitry. Some higher-end amps may have a parametric equalizer (or a semi-parametric equalizer) for some frequency ranges, which can be used to modify the bass tone to suit different styles or performance venues. Some bass amps have a 20 dB pad which can be used to attenuate "hot" signals, such as basses with an internal preamplifier (depending on the model of amplifier, some brands may provide two inputs (high and low gain) instead of providing a "pad".

Some bass amps may have additional controls for onboard effects such as bass chorus or a knob for controlling a multieffects unit (which might include a suboctave generator, chorus, etc.). Some 2000s-era amps may have a knob to control amp or speaker emulation settings (e.g., emulating the tone of a bass stack, a vintage tube amp, etc.).

Input and output jacks[edit]

This rear view of an Eden WT-400 Traveler Plus amplifier head shows various jacks, including 1/4" speaker output, a 1/4" signal out (to plug into a second amplifier, if needed), a "send" and "return" jack for creating and effects loop, a DI output, auxiliary left and right inputs and a tuner out jack.

Bass amps come with a range of different input and output jacks, depending on the cost of the amplifier and its intended purpose. The least expensive practice amps may only have a single 1/4" input jack and no output jacks. Some practice amps and small combo amps have RCA or 1/8" inputs for plugging an MP3 player or CD player into the bass amp, to facilitate practicing with a recording. Lower end amps may have a preamp out. While this signal can be plugged into a mixing board, it is preferable to use a DI output for this purpose because a preamp out is an unbalanced signal. Bass amps intended for use by professional players may have an XLR DI output so that the amp can be connected directly to a mixing board of a PA system or recording set-up. Some bass amps have a 1/4" headphone out jack, so that the bass amp can be used for silent practice. When the headphone is plugged in, the amplifier to the speaker is normally turned off. Higher end amps often have "preamp out" and "power amp in" jacks to make an effects loop.

Some bass amps have two inputs. One some amps, one is a high gain input and the other is a low gain input. On other amps, the two inputs may be intended so that two basses can be plugged in at the same time. On these amps, there is usually a separate volume control for each input; this is done to enable a bass player to switch between two instruments on different songs (e.g., a fretted and fretless bass) without having to unplug and plug in jacks. Some bass amps also have an external speaker out jack. While this jack is also 1/4", a speaker cable must be used with this jack, rather than a patch cord, because it sends a powered signal out to an external speaker cabinet. On some amps with a number of input and output jacks, the jacks may be consolidated in a patch bay. Some amps have an input jack for a foot-operated switch which can be used to turn on an effect or switch to a solo channel. Some higher-end amps have a Speakon speaker jack for an extension speaker. Some amplifiers have a "tuner out" jack, for sending the signal to an electronic tuner.

A small number of bass amps designed for the upright bass have both a 1/4" input for a piezoelectric pickup and an XLR input for a condenser microphone mounted on the bass, with a simple mixer for combining the two signals, as described below.

Indicator LEDs[edit]

A DNA-1350 amp head; note the three indicator LEDs on the right-hand side, indicating amplifier status.

The least expensive practice amps and basic combo amps may only have a single indicator light: an LED to indicate when the amp's power is on. More expensive amps may also have LEDs to indicate when the preamp has a signal present, when a limiter or similar speaker protection feature is activated, when clipping is occurring, or when the amp is in standby mode. Amps with a built-in tuner typically have several LEDs to indicate when the note being played is flat, sharp, or in tune.

Amplifying the double bass[edit]

A jazz bassist performing on an upright bass, using an amplifier and speaker to augment the instrument's natural volume

Almost all bass amplifiers are designed for use with an electric bass, which has magnetic pickups. When a double bass player is plugging her instrument into a typical bass amp, the signal usually comes from a piezoelectric pickup mounted on the bridge or beneath the feet of the bridge. The direct signal from a piezoelectric pickup does not usually sound good when it is plugged into a standard electric bass amp. Many upright bass players who use piezoelectric pickups use a preamplifier or preamp-equipped DI box before the signal is sent to the bass amp. The preamplifier helps to ensure that the impedance of the pickup signal matches the impedance of the amplifier, which improves the tone. Some preamplifiers also have equalizers which can be used to modify the tone.

Double bass players performing in genres where the bass is slapped, either by pulling the string until it snaps back onto the fingerboard or striking the strings, such as traditional blues, rockabilly, psychobilly jazz, folk, and bluegrass often blend the sounds picked up by a piezoelectric transducer with the sounds picked up by a small condenser microphone mounted on the bridge. The microphone picks up the resonance coming from the body and the sounds of the strings being plucked, bowed, or slapped. The two sound signals are blended using a simple mixer and then routed to the amplifier. While many upright bass players use combo amplifiers, bassists in genres that use high stage volume, such as the punk-rockabilly genre of psychobilly use "bass stacks". Some jazz bassists and other bass players who play in small venues use specialized, expensive upright bass amps, like the Acoustic Image combo amplifier.

Double bass players playing in genres where a louder amplified tone (emphasizing the fundamental frequencies) is desired for the bass may be more likely to face the problem of audio feedback. Feedback for double bass generally manifests itself as a sharp, sudden high-volume "howling" sound that can damage loudspeakers. When acoustic instruments with resonant bodies are amplified with microphones and piezoelectric transducer pickups, the common approach used for amplified double basses, they are prone to have feedback problems. For acoustic bass guitars, soft plastic discs are available to block the sound hole, thus reducing feedback. Upright bass players sometimes use homemade foam or styrofoam inserts to fill in the "f" holes of the double bass, which can reduce feedback.

Other ways to reduce feedback include: playing with the bass amp's speaker cabinets in front of, rather than behind, the instrument; reducing the onstage volume; signal phase reversing; using a parametric equalizer or "notch filter" EQ to turn down the frequency that is feeding back; or using "feedback eliminators", which are basically automatic notch filters that find and turn down the frequency that is "howling."

Preamplification and effects[edit]

The basic sound of the amplified electric bass or double bass can be modified by electronic bass effects. Since the bass typically plays a beat keeping role in many styles of music, preamplifiers, compression, limiting, and equalization are the most widely used effects for bass. The types of pedals commonly used for electric guitar (phaser, flanger, etc.) are less commonly used for bass, at least in bands or styles where the bassist mainly plays a rhythm section role. In styles of music where the bass is also used as a soloing instrument (certain genres of heavy metal, progressive rock and jazz fusion, bassists may use a wider range of effects units.

A range of other effects are used in various genres. "Wah-wah" and "synth" bass effects are associated with funk music. As well, since the 1960s and 1970s, bands have experimented with "fuzz bass" where the bass is distorted either by overdriving the amp or by using a distortion unit. Octave-generating effects, which generate an octave below the pitch being played are also used by bass players. Many bassists in modern-day hard rock and heavy metal bands use overdrive pedals made for bass guitar. Since the late 1980s, bass-specific overdrive pedals have been available; these pedals maintain the low fundamental pitch. Using a regular guitar distortion pedal for bass would result in the lower frequencies being greatly lessened. Well-known overdrive effects for bass include the BOSS ODB-3 Bass Overdrive[1], Electro-Harmonix Bass Blogger[2], Tech21 Sansamp Bass Driver[3][4], the DigiTech|DigiTech XBD Bass Driver [5], and the Electro-Harmonix Big Muff.

Overdrive built into amplifiers[edit]

Over the years, various Peavey bass amplifiers have had built-in distortion effects.

Some bass amplifiers have an "overdrive" or distortion effect built into the unit. The Peavey Century 200 has an onboard "distortion" effect on the second channel. The Peavey VB-2 also has built-in overdrive. Aguilar Amplification's AG 500 bass head is a two-channel amplifier, one of which offers a "saturation" control for overdrive. A variety of BOSS combo amplifiers have a built-in "drive" effect. Gallien-Krueger's bass amp heads have a "boost" control which provides a simulated tube overdrive effect. The Behringer Ultrabass BVT5500H Bass Amplifier Head has a built-in limiter and overdrive. The LowDown LD 150 bass amp has a range of overdrive sounds, from a slight hint to heavy distortion. The CUBE-20XL BASS amp includes built-in overdrive.

The 75 Watt Fender Rumble 75 Bass Combo Amp and its 150 Watt and 300 Watt counterparts can produce an overdrive effect by using the gain and blend controls, giving overdrive sounds ranging from "mellow warmth [to] heavy distorted tones".[11] The Fender SuperBassman is a 300-watt tube head which has a built-in overdrive channel. The Fender Bronco 40 includes a range of effects including modern bass overdrive, vintage overdrive and fuzz.

Lemmy Kilmister, the bassist for Motorhead, obtained a natural fuzz bass tone by overdriving his twin 100 watt Marshall Bass stacks.

The MESA Bigblock 750 has a built-in overdrive channel. The Mesa M2000 has a high gain switch which can be engaged with a footswitch. The Marshall MB450 head and combo bass amplifiers have a tube pre-amp on the "Classic" channel which can be overdriven. The Ashdown ABM 500 EVO III 575W Bass amp head has a built-in overdrive effect. Overdrive is also available on many Crate bass amplifiers. The Yamaha BBT500H has three types of built-in drive effects: overdrive, distortion and fuzz. The Ampeg B5R Bass Amplifier has two channels: clean and overdrive, with the ability to combine the two.

Verellen, a boutique amp company, produces a bass amplifier with a built in overdrive channel.

Manufacturers[edit]

A bass amp head used with two speaker cabs, with each cabinet containing two loudspeakers and a high frequency horn.

Bass amplifier equipment manufacturers include a variety of different types of companies, ranging from companies that only make individual components (e.g., Accugroove loudpeakers, a speaker manufacturer) to companies that only make bass amplifiers and loudspeakers (e.g., Gallien-Krueger). At the other end of the spectrum are companies that offer bass amplification equipment as part of a much broader offering of different types of instrument amplifiers and public address systems (e.g., Peavey, Carvin A&I or Yorkville Sound.)

Another way of categorizing bass equipment manufacturers is by which part of the market they are targeting. While Peavey and Yorkville products are aimed at the generalist mass market, some bass equipment manufacturers, such as Acoustic Image or Walter Woods make expensive "boutique" equipment that is aimed at a niche market within the professional musician market. Acoustic Image amplifiers and speaker cabinets tend to be used by professional acoustic folk and jazz musicians, and Walter Woods amplifiers are associated with professional acoustic jazz bass players.

Some of the best-known and most notable companies include:

See also[edit]

References[edit]