Amp Glossary
A B C D E F G H I L M N O P R S T V W
AC (alternating current) Electric
current that reverses its direction (alternates) at regularly occurring
intervals. Power from a standard wall socket is generally 110 to 120 volts
AC, alternating at 60 cycles per second. Audio signals in amps, effects,
wires, etc., are also AC. See DC.
AC outlet Frequently referred to as a convenience or courtesy outlet (usually found on the back of an amp), this feature provides an extra socket for powering auxiliary equipment.
Active Pertaining to electronic circuits (e.g., tone controls) that add to as well as subtract from a given signal. Such circuits often require power sources. See Passive.
Active tone controls Tone controls that add to and attenuate, rather than just cut from, an audio signal.
Amplifier (amp) An electronic device that increases the level of an audio signal, usually for the purpose of driving one or more loudspeakers, or for maintaining proper levels in long signal chains (multiple effects, long cords, etc.).
Balanced connector A 3-conductor connector - commonly
referred to as an XLR or Cannon connector that terminates a cord carrying
a signal over three wires. One wire acts as a ground, while the others
carry the signal in the form of positive and negative voltages.
Bass control - A tone control that affects low audio frequencies (typically below 500Hz).
Biamping The utilization of two amplifiers in a given sound system in order to separately amplify different frequency ranges and thereby reduces distortion. Usually, a full-range audio signal is divided by means of an electric crossover; one amp is designated for low frequencies, while the other is designated for highs.
Bright switch A feature that emphasizes an amps high-frequency range.
Cascading Switching or wiring in extra preamplifier
stages in series to achieve higher gain.
Channel A complete sound avenue, usually consisting of a preamp, a voltage amp, a power output, and power supply stages.
Channel switching A feature that allows an audio signal to be routed from one channel to another, usually by means of a footswitch.
Chassis The sheet-metal frame to which electronic components (capacitors, transistors, resistors, etc.) are mounted.
Circuit breaker A device found on the backs of some amplifiers that automatically interrupts a circuit carrying potentially damaging current; often used instead of a fuse.
Compression A feature of some amps and effects that reduces the signals dynamic range by making loud sounds quieter and quiet sounds louder. See Limiter.
Crossover A circuit that divides a signal into two or more bands of selected frequencies; often used in biamping or triamping.
Crossover distortion Distortion caused by a slight delay in amplification at the crossing-over point between the top and bottom devices in a push-pull amplifier circuit.
dB (decibel) A unit of measurement for expressing the ratios of various quantities including sound level, power, and voltage.
DC (direct current) Electric current that has constant and uniform polarity (flows in one direction). Batteries and small power sources for effects provide a source for DC. See AC.
Depth A general term often used in describing the intensity of an effect such as reverb, phasing, etc.
Distortion Also referred to as clipping, distortion is a change in an audio signal resulting in the appearance of frequencies at the output that were not present in the original waveform. Distortion is commonly caused by applying a signal that is too powerful for an amp, speaker, or other electronic device to adequately handle. It is commonly employed as a means of creating sustain.
Distortion effect A feature that intentionally causes an amp to sound as if it were being overdriven.
Dynamic range The difference between the minimum and maximum (overload) signal level in audio equipment, often measured in decibels.
Effects channel A channel that includes an effects device (phaser, distortion, flanger, etc.).
Effects loop Often composed of an output jack and an input jack that allow effects to be connected between the preamp and the power amp (or a successive preamp) in an amplifier. Because the signal level from a preamp is much higher than that derived from most guitars, the signal-to-noise ration can be greatly increased by using an effect between amp stages rather than between the instrument and the amp.
EQ (equalization) The intentional altering of portions of the audio-frequency spectrum by means of filters or tone controls; often employed to reduce uneven frequency response or feedback.
Extension-speaker jack A feature usually found on the back of an amp that allows a remote speaker to be used.
Feedback Self-oscillation caused by a regenerating signal loop between the guitar pickup or microphone and the amp and speaker.
FET (field-effect transistor) A kind of solid-state device that is often more stable than standard transistors.
FET distortion When overdriven, a FET exhibits distortion qualities more like those produced by a tube than most other types of transistors.
FET switching Circuits containing FETs, which can be used to activate effects or perform channel-switching functions with low noise and low power consumption.
Footswitch A foot-triggered switch used to activate an amps reverb, vibrato, or other feature, as well as effects devices.
Frequency response The range of frequencies over which a device or audio system will perform.
Fuse A replaceable protective device that breaks a circuit when the current becomes abnormally high. A fast-blow fuse is generally used in delicate circuits, whereas a slow-blow fuse is use in more rugged ones. See Circuit Breaker.
Fuse holder A socket or metal clip that allows for easy replacement of a fuse. Generally located on the back of an amp or within the chassis.
Gain The amount an amplifier increases the power of a signal, usually expressed in decibels. See Volume.
Gain boost Increasing the amount of amplification or gain.
Graphic equalizer A device containing multiple filters with separate, fixed frequency centers, which allows for boosting or cutting particular signal ranges. See Parametric Equalizer.
Ground (also called earth) The electrically neutral part of a circuit, often referred to in terms of 0 volts.
Ground switch Also referred to as a reverse or polarity switch, this feature allows the polarity of a current to be conveniently reversed, resulting in the elimination of hum.
Headroom A term that expressed the relative difference between the operating and maximum operating points of an audio device.
Heat sink A metal part with maximized surface areas designed to dissipate heat generated by electronic components.
Hertz (Hz) A unit equal to one cycle per second that measures the frequency of a periodic phenomenon such as an alternating current.
Hiss - A kind of undesirable audio frequency noise. Often called white, pink, or thermal noise.
IC (integrated circuit) Also known as a chip, an IC is a sophisticated, highly miniaturized solid-state circuit that contains the equivalent of many components such as transistors, resistors, capacitors, diodes, etc.
Impedance Measured in ohms, impedance is the total opposition to the flow of alternating current in a circuit.
Inputs The entry points where the signal from a guitar of effect may be introduced to an amplifier or other electronic device.
LED (light-emitting diode) A small light (often red, green, or yellow) commonly used as an indicator.
Limiter An electronic circuit that acts much like a compressor, except it keeps the dynamic range of a signal within fixed limits.
Line level Usually referred to as a signal level of) dB. Equivalent to a 0.7 to 1-volt signal level into specified impedance.
Master volume Simultaneously controls the overall volume of one or more channels of an amp. When used in conjunction with a channels volume control, a master volume enables a guitarist to control the amount of distortion as well as the overall output of the amp.
Matched tubes Vacuum tubes selected for their similar electrical characteristics. Often employed in amps to produce more efficient operation.
Matching impedance When the output impedance of a device is compatible with the input impedance of a device to which it is connected, the two are said to match. Mismatched impedances can lead to distortion, signal loss, or poor frequency response.
Microphonic Sensitivity to vibrations causing noises and ringing. Tubes are especially prone to microphonics and will self-oscillate.
Midrange control A tone control that affects audio frequencies in the middle range, where the largest concentration of audio energy is usually present.
Noise floor The level at which noise (hiss, hum, etc.) exists in an amplifier. Often used as a reference point in signal-to-noise ratios.
Ohm Symbolized by the Greek letter omega, an ohm is the unit used to measure electrical resistance or impedance.
Open back A speaker cabinet with no back. The speaker is then unloaded.
Oscillation Any kind of signal or alternating current including those beyond audibility.
Outputs Jacks normally situated on the back of an amp that allow one or more auxiliary speakers to be attached.
Overdrive level The level at which distortion begins as a consequence of feeding a device with an overloading signal.
Overload A load that exceeds an amplifiers capability.
Parametric equalizer An equalizer with one or more center frequencies that are variable over a particular range, in addition to boost and cut capabilities. See Graphic Equalizer.
Passive Pertaining to electronic circuits that generally subtrack from a signal, and which require no power source. See Active.
Passive tone controls Tone controls that only attenuate, or cut from, an audio signal. Generally a simple circuit, such as a pot and a capacitor, requiring no external power. See Active Tone Controls.
Peak wattage Also referred to as peak power, peak wattage is the maximum instantaneous power of a signal. Amplifiers are able to perform at their peak for only short periods of time. See RMS.
Piggyback Refers to an amp and speaker cabinet combination in which the head (amp circuitry) and speakers are not housed in the same enclosure.
Pilot lamp A light that indicates whether an amp or other electrical device is turned on.
Potentiomenter (pot) A variable resistor used for an amplifiers volume and tone controls.
Power Working electrical energy measured in watts.
Power amp An amplifier that has higher-power output capability than a preamp and is designed to drive one or more loudspeakers. Generally contained with the preamp in self-contained or piggyback amps, but also available as a separate unit in some cases.
Power amp in An input that plugs directly into an amps power amplifier and bypasses the preamp. This function allows some amps to be used as slaves.
Power attenuator A device used to soak up power or allow less power transmission between amp and speaker.
Power rating The maximum power at which an amplifier can operate over a specified period.
Preamp A stage in an amplifier that raises the signal of a low-level source (such as a guitar) so that it may be further processed.
Preamp out An output that facilitates taking the preamps signal and sending it to other power amps, PA mixers, or recording gear.
Push-Pull switch A switch that is operated by a pulling or pushing movement; often combined with a potentiomenter.
Reverb The synthetic creation of ambience, or reverberation (echoes spaced so closely together that they are no longer discernible as individual events), most commonly by means of sending a signal through an electronic delay device. In most amps, a module containing metal springs provides the delay.
RMS (root mean square) The true measure of an amps ability to perform, RMS is based on continuous power at a given number of cycles per second over a period of time not less than 30 seconds. See Peak.
Self-contained amp An amplifier and speaker that are housed in the same cabinet.
Sensitivity The quantity of input signal level usually specified to allow the amplifier to go to full power with all the controls up.
Slave A power amplifier that is driven by the preamp of another amp or PA component; often used to provide extra power or to drive cross-stage monitor amps.
Solid state Refers to electronic components such as diodes and transistors that use semiconductors (crystals) instead of tubes.
Speaker A device that converts electrical energy into sound waves.
Speaker cone The cone-shaped part of the speaker that actually works as a piston to cause air motion and consequently sound.
Standby switch A feature that allows tubes to idle (remain warm) while an amp is not in use; e.g., between sets. This reduces the strain on tubes caused by frequent heating and cooling.
Sustain The phenomenon in which a sound lasts without appreciable degradation or decay.
Toggle switch A two or three position switch operated by flipping (toggling) a protruding lever.
Top (head) An amplifier unit that is separate from any type of speaker enclosure.
Transducer A device that converts electrical energy into mechanical energy, such as a speaker.
Transformer Commonly a large, square-shaped or toroidal (doughnut-shaped) component used in the power supply of an amplifier to convert AC main voltage to other suitable voltages. Transformers are sometimes employed as buffers between amps and speakers in order to match their impedances.
Transient response The ability of an amplifier to handle sudden changes in audio levels without distortion.
Treble boost Electronic augmentation of high-frequency signals.
Treble control A tone control that affects high audio frequencies (typically above 5000Hz).
Tremolo An effect feature on many amps, tremolo is the variance in the amplitude (volume) of a sound generally at a rate between .5 and 20 times per second achieved by the use of a low-frequency oscillator. Commonly mistaken for vibrato.
Triamping The utilization of three amplifiers in a given sound system; one each for bass, midrange, and treble frequencies. It utilizes the same basic principle for avoiding distortion as biamping.
Tube Also referred to as a vacuum tube or valve, a tube is a sealed glass envelope in which the conduction of electrons takes place througha gas or vacuum; most often for amplification or switching applications.
Variac A variable transformer that can change the AC line voltage. It is used to control amplifier power by raising or lowering the AC voltage.
Vibrato An effect feature that uses an oscillator to cause a regular variation in the frequency (pitch) of a sound. Speed and intensity controls for governing the velocity and depth of the vibrato effect are commonly present on the front panels of amps with this feature.
Voice coil The central part of the speaker that converts electrical pulses into magnetic pulses. It consists of a wire coil would around a cylindrical form.
Voltage Electrical pressure that causes current to flow through a conductor. Its unit of measurement is the volt.
Volume The overall
amount of loudness. See Gain.
Wattage The power capability of an amplifier.
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