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A guitar amplifier (or guitar amp) is an electronic amplifier that amplifies the electrical signal from a pickup on an electric guitar, bass guitar, or acoustic guitar so that it can produce sound through a loudspeaker, which is typically housed in a wooden cabinet. A guitar amplifier may be a standalone wood or metal cabinet that contains only the amplifier (and preamplifier) circuits—or it may be a "combo" amplifier, which contains both the amplifier and one or more speakers in a wooden cabinet. Most guitar amplifiers can also modify the instrument's tone by emphasizing or de-emphasizing certain frequencies and adding electronic effects, typically distortion and reverb. The input of modern guitar amplifiers is a 1/4" jack, which is fed a signal from a piezoelectric pickup (usually from an acoustic guitar) or an electro-magnetic one (from an electric guitar). This article focuses on electric guitar amps For information on amps for bass guitar, see the article on bass amps. ==Structure== Typically, guitar amplifiers have two amplifying circuit stages, and in addition frequently have tone-shaping electric circuits. The first is a preamplifier stage (there may be more than one), which amplifies the guitar signal to a level that can drive the power stage. The power amplifier or output stage produces a high current signal to drive a speaker to produce sound. There may be one or more tone stages that affect the character of the guitar signal: * Before the preamp stage (as in the case of guitar pedals) * Between the preamp and power stages (as in the cases of effects loop or many dedicated amplifier tone circuits) * Between multiple stacked preamp stages * In feedback loops from a post-preamp signal to an earlier pre-preamp signal (as in the case of presence modifier circuits) Tone stages may also provide electronic effects—such as equalization, compression, distortion, chorus, or reverb. Amplifiers may use vacuum tubes (called valves in Britain), solid-state (transistor) devices, or both. There are two configurations of guitar amplifiers: combination ("combo") amplifiers, which include an amplifier and one or more speakers in a wooden cabinet, and the standalone amplifier (often called a "head" or "amp head"), which does not include a speaker, but passes the amplified signal via a speaker cable to a speaker cabinet. A wide range of speaker configurations are available in guitar cabinets, ranging from cabinets with a single speaker (e.g., 1×10" or 1×12") or multiple speakers (e.g., 2×10" or 4×10"). Guitar amplifiers range in price and quality. Music equipment companies import small, low-powered practice amplifiers for students that sell for less than $50 USD. Other companies produce expensive custom-made amplifiers for professional musicians, which can cost thousands of dollars. Most combo amplifiers have a carrying handle, and many combo amplifiers and cabinets have metal or plastic-reinforced corners. Control knobs are typically mounted on the front of the cabinet or chassis, though in some cases, the knobs are on a recessed panel at the back of the top of the amplifier. The most basic amps only have a few knobs, which typically control volume, bass and treble. More expensive amps may have a number of knobs that control pre-amp volume (or "gain"), distortion or overdrive, volume, bass, mid and treble, and reverb. Some older amps (and their re-issued versions) have a knob that controls a vibrato effect. The 1/4" input jack is typically mounted on the front of the amplifier. In the simplest, least expensive amplifiers, this 1/4" jack is the only jack on the amplifier. More expensive amplifiers may have a patch bay for multiple inputs and outputs, such as a pre-amp out (for sending to another guitar amplifier), an in jack to create an effects loop (when use with the pre-amp out), an external speaker output (for powering an additional speaker cabinet), and stereo RCA jacks or an 1/8" jack, for connecting a CD player or MP3 player. Some amps have a 1/4" jack for connecting a pedal to turn the amp's onboard overdrive and reverb on and off. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Guitar amplifier」の詳細全文を読む スポンサード リンク
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