Keyboard amplifier
A keyboard amplifier is a powered electronic amplifier and loudspeaker in a speaker cabinet used for the amplification of electronic keyboard instruments. Keyboard amplifiers are distinct from other types of amplification systems such as guitar amplifiers due to the particular challenges associated with making keyboards sound louder on stage; namely, to provide solid low-frequency sound reproduction for the deep basslines that keyboards can play and crisp high-frequency sound for the high-register notes. Another difference between keyboard amplifiers and guitar/bass amplifiers is that keyboard amps are usually designed with a relatively flat frequency response and low distortion. In contrast, many guitar and bass amp designers purposely make their amplifiers modify the frequency response, typically to "roll-off" very high frequencies, and most rock and blues guitar amps, and since the 1980s and 1990s, even many bass amps are designed to add distortion or overdrive to the instrument tone.
Keyboard amplifiers differ from guitar amplifiers and bass amplifiers in that whereas guitar and bass amps are usually designed for use with one guitar at a time, keyboard amplifiers almost always have a mixer with inputs for two, three, or four keyboards, because many performers often use multiple keyboards. For example, a single player may perform with a stage piano, a keytar and a synthesizer keyboard. Each channel input typically has its own pre-amplifier and volume knob. Keyboard amps in the lower cost range and power output range may only provide equalization controls for the overall mix. Higher-priced, higher power output keyboard amps designed for professionals may have equalizer controls for each channel. Keyboard amplifiers also differ from guitar amps and bass amps in that whereas many guitar and bass amplifier companies often sell standalone amplifier units for use with one or more separate speaker enclosures, keyboard amplifiers are almost always combination amplifiers, so-named because they combine a preamplifier, power amplifier, full-range speaker, and a horn-loaded tweeter, all in a single wooden speaker cabinet.
Two notable exceptions to the "low distortion" rule are keyboard amplifiers designed for the Hammond organ or clonewheel organs and amps used with electric pianos such as the Fender Rhodes. With organs used in blues or hard rock, performers often use the vintage Leslie speaker cabinet and modern recreations, which have a tube amplifier which is often turned up to add a warm, "growling" overdrive to the organ sound. With electric pianos used in a rock or funk band, natural tube overdrive is often added to the sound.
Design
Since keyboards have a very wide range of pitches, from deep bass notes to very high treble notes, keyboard amplifiers have to provide solid low-frequency sound reproduction and crisp high-frequency sound reproduction. This distinction affects the design of the loudspeakers, the speaker cabinet and the preamplifier and amplifier. They usually include tuned bass reflex ports or vents for increased efficiency at low frequencies. Since keyboard amplifiers have to be able to reproduce very high notes, they are often equipped with a tweeter, which may be mounted in a horn.Comparison with guitar and bass amplifiers
While electric guitar amplifiers are typically designed to modify the tone of the guitar, keyboard amplifiers intended for general use for a range of keyboard applications usually have very low distortion and extended, flat frequency response in both directions. Electric guitar amp combos and amps are usually designed to add coloration to the guitar tone or "sweeten" the tone. Keyboard amp combos are usually designed to reproduce the input signals. The exception to this rule is keyboard amplifiers designed for the Hammond organ, such as the vintage Leslie speaker cabinet and modern recreations, which have a tube amplifier which is often turned up to add a warm, "growling" overdrive to the organ sound. Electric piano players in rock and funk also often seek to add natural tube overdrive to their sound.Unlike bass amplifiers and electric guitar amplifiers, keyboard amplifiers are rarely used in the "amplifier head" and separate speaker cabinet configuration. Instead, most keyboard amplifiers are "combo" amplifiers that integrate the amplifier, tone controls, and speaker into a single wooden cabinet. Another unusual aspect of keyboard amplifiers is that they are often designed with a "wedge" shape, as used with monitor speakers. This permits them to be used as monitor speakers which is more suitable for a seated keyboardist.
Design features
Keyboard amplifiers often have an onboard three or four-channel mixer, so that multiple keyboards can be plugged into one amplifier and so that keyboardists can control the tone and level of several keyboards. In some genres, such as progressive rock, for example, keyboardists may perform with several synthesizers, electric pianos, and electro-mechanical keyboards. Keyboard amplifiers often have onboard reverb effects.Most inexpensive to mid-priced amplifiers currently produced are based on semiconductor circuits. Solid-state amplifiers vary in output power, functionality, size, price, and sound quality in a wide range, from practice amplifiers to professional models. The smallest, most inexpensive practice amplifiers may have only two channels with volume controls and one or two tone controls. Home practice amps have from 20 to 30 watts of power, often through an 8" or 10" speaker. Small keyboard amplifiers designed for small band rehearsals have 50 to 75 watts, a 12-inch speaker, and possibly a tweeter. Large keyboard amplifiers designed for shows in large clubs or halls have 200 to 300 watts of power, a 12-inch or 15-inch speaker, and a horn-loaded tweeter.
Some keyboard amps may be equipped with a compressor or limiter to protect the speaker from damage when the amplifier is being used at high volume levels. Some keyboard amps have an extension speaker jack, which enables the amp to be connected to a second speaker cabinet for more volume.
Use in performances
In small venues such as a coffeehouse or small bar, a keyboardist might not connect the keyboard amp up to the PA system, and just use the sound of the keyboard amp to provide the keyboard sound for the venue. At most mid-sized venues and all large venues, such as stadiums, the signal from the keyboard amp's pre-amp out jack, DI out jack and/or the microphoned sound from the speaker and horn are fed to the mixing board and then amplified with the PA system or sound reinforcement system. In cases where a keyboardist has a rotating Leslie speaker, microphones are always used to pick up the sound, rather than taking an electronic signal from the amp, because only a mic can capture the unique sound of Leslie's rotating horns and speaker drum.Comparison with PA systems
In the 2010s, there was some convergence between the functionality of keyboard combo amplifiers and small PA systems. Some keyboard amplifiers have an XLR input for a microphone and a microphone preamplifier. To use a microphone, a preamp is generally needed to boost the power of the signal because mic's only output a tiny, weak signal. This input's inclusion of a preamp means that it could also be used to plug in an acoustic guitar's piezoelectric pickup. This type of keyboard amplifier could be used as a PA system by a singer-songwriter who is accompanying herself or himself on guitar and keyboards in a very small venue, such as a coffeehouse.Keyboard amps with an XLR mic input, preamplifier and a multichannel mixer are in effect small combo PA systems. While small combo keyboard amps with mic inputs became widely available on the market in the 2000s and were promoted as an innovation, in fact, the first portable PA systems sold in the 1920s and 1930s were "combo" systems, in which a power amplifier and speaker were combined in a single wooden cabinet. Instrument amplifiers from the 1950s and 1960s still sometimes included inputs for microphones, as few portable PA systems were available for garage bands during this era. By the 1970s and 1980s, though, portable PA systems were typically sold as three-piece sets: an amp-mixer containing a small mixer and a power amplifier integrated into a single amp head-style chassis with a handle, and two separate PA speakers. The speakers were typically connected to the amp-mixer with speaker cables. Providing separate speakers, enabled bands to elevate the speakers and place them at either side of the stage, which improved sound dispersion over the former approach of using instrument amplifiers to boost both instrument and vocal sounds.
There are several limitations to using a combo keyboard amp as a small PA system. First, it is hard to elevate a keyboard amp's speaker the way most PA speakers can be raised up, using PA system speaker stands with a pole onto which most small- to mid-sized PA speaker enclosures can be mounted using their base-mounted metal socket. Elevating a PA speaker above the audience helps to ensure that the sound is dispersed to the whole audience; if a combo keyboard amp is used as a small PA, the keyboard amp is typically placed on the floor or raised a bit by placing it on a table. In this scenario, the sound produced by the keyboard amp would be absorbed by the first several rows of audience members, and people in the back of the venue might not be able to hear the performance. Second, most small, low-wattage keyboard amps do not produce enough volume to clearly project the lead vocals into the venue so that they are at the "front of the mix", a sound preferred in many pop genres. For example, whereas a small PA system for a coffeehouse would typically have 100 watts, a small keyboard combo amp may only be rated at 20 watts. Third, while the vast majority of small PA systems come with two speaker cabinets, most combo keyboard amps have a single speaker cabinet. With two speaker cabinets, even if both are pointing straight out at the audience, this provides better coverage of the room; moreover, the two speaker cabinets can be angled outwards a bit, increasing the arc of coverage better for wide rooms.