A power attenuator, used with a guitar amplifier, is a type of attenuator that diverts and dissipates a portion of the amplifier's power to enable hearing the amplifiers high-volume characteristics at lower volume.

Explanation

Musicians playing through

vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. The type kn ...

guitar amplifiers A guitar amplifier (or amp) is an electronic device or system that strengthens the electrical signal from a pickup on an electric guitar, bass guitar, or acoustic guitar so that it can produce sound through one or more loudspeakers, which ar ...

sometimes want to produce

distortion In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signal ...

by overdriving the amplifier's output stage. Under such a condition, the amplifier is close to or at its maximum output power. The resulting volume level is unsuitable for many playing conditions. By reducing the power to the speaker, a power attenuator reduces the volume without altering the overdriven quality of the tone. The most common approach to power attenuation is a ''power soaker'', which absorbs a portion of the power and dissipates it as heat. This device connects between the amplifier output and the guitar speaker. A typical attenuator circuit is the

L pad An L pad is a network composed of two impedances that typically resemble the letter capital "L" when drawn on a schematic circuit diagram. It is commonly used for attenuation and for impedance matching. Speaker L pad A speaker L pad is a spe ...

. A variable L pad is a power divider circuit that provides an adjustable power level to a speaker while maintaining a constant load impedance on the amplifier. Another approach uses a

variac An autotransformer is an electrical transformer with only one winding. The "auto" (Greek for "self") prefix refers to the single coil acting alone, not to any kind of automatic mechanism. In an autotransformer, portions of the same winding act as ...

or power scaling circuit, which reduces the B+ supply voltage available to the power tubes thus producing power tube distortion at a reduced level, while all available output power still goes to the guitar speaker. The Variac method bears the risk that voltage to the tubes can damage the

filament The word filament, which is descended from Latin ''filum'' meaning " thread", is used in English for a variety of thread-like structures, including: Astronomy * Galaxy filament, the largest known cosmic structures in the universe * Solar filament ...

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...

if operated beyond manufacturer specifications. In a power scaling circuit, by decreasing just the B+ plate voltage, the cathode bias and screen grid voltage decrease proportionately, while the filament voltage stays constant. However the term power attenuator may be a misnomer for this type of power control, because lowering B+ voltage tends to increase distortion, where by convention, an attenuator should not introduce distortion. Power damping is an output level control method that involves the phase inverter and a potentiometer. The potentiometer lets the musician overdrive that at reduced output, similar to a post phase inverter master volume (PPIMV) control.

Description

A power attenuator can be either purely resistive, or mostly resistive and partly

reactive Reactive may refer to: *Generally, capable of having a reaction (disambiguation) *An adjective abbreviation denoting a bowling ball coverstock made of reactive resin *Reactivity (chemistry) *Reactive mind *Reactive programming See also *Reactanc ...

. The original guitar amp power attenuator, the Altair Attenuator, was primarily resistive, used a

rotary switch A rotary switch is a switch operated by rotation. These are often chosen when more than 2 positions are needed, such as a three-speed fan or a CB radio with multiple frequencies of reception or "channels". A rotary switch consists of a spindle ...

to select taps on a

toaster A toaster is a small electric appliance that uses radiant heat to brown sliced bread into toast. Types Pop-up toaster In pop-up or automatic toasters, a single vertical piece of bread is dropped into a slot on the top of the toaster. ...

coil with low inductance windings. Another early model, simply called 'Power Attenuator' by Active Guitar Electronics, used continuously variable power

rheostat A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat. The measuring instrume ...

s. Other models, such as the Marshall Power Brake, add some electrical

inductance Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The flow of electric current creates a magnetic field around the conductor. The field strength depends on the magnitude of the ...

capacitance Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are ...

to the electrical load (including

fans Fan commonly refers to: * Fan (machine), a machine for producing airflow, often used for cooling ** Hand fan, an implement held and waved by hand to move air for cooling * Fan (person), short for fanatic; an enthusiast or supporter, especially wit ...

light bulb An electric light, lamp, or light bulb is an electrical component that produces light. It is the most common form of artificial lighting. Lamps usually have a base made of ceramic, metal, glass, or plastic, which secures the lamp in the soc ...

s and coils). There is debate about whether reactive attenuators do a better job of preserving a guitar amplifier's tone. A guitar amplifier power attenuator may also offer a

line-level Line level is the specified strength of an audio signal used to transmit analog audio between components such as CD and DVD players, television sets, audio amplifiers, and mixing consoles. Line level sits between other levels of audio signals. ...

output jack for sending the distortion-processed signal through an effects chain, to a recording console, or for the purpose of re-amplifying signal through a larger or smaller amplifier. If the amplifier is designed to accommodate routine full power use, an attenuator neither increases nor reduces the potential for amplifier damage. An early guitar amplifier that included a power attenuator was the Jim Kelley amplifier, which came with its own L-pad type attenuator. Some production attenuators are the Scholz Power Soak,

Marshall Marshall may refer to: Places Australia * Marshall, Victoria, a suburb of Geelong, Victoria Canada * Marshall, Saskatchewan * The Marshall, a mountain in British Columbia Liberia * Marshall, Liberia Marshall Islands * Marshall Islands, an i ...

Power Brake, THD Hot Plate, Weber MASS, Audiostorm HotBox and ARACOM.

References

External links

Jedistar Attenuator PageAdam's amps - Basic attenuator circuits
{{DEFAULTSORT:Power Attenuator (Guitar) Electric guitars Noise reduction Loudspeaker technology