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Grinding The Axe

By Eddie Ciletti
After exploring the concepts of Resistance and Impedance (My Piece de Resistance!; Impedance 101: Part Two), I am ready to zoom out and enjoy some guitar sounds. Well, provided no noises get in the way. The key issue is gobs of Gain, making it easy to understand how any noise - hum, buzz, hiss or nearby radio station - gets amplified along with the more musical and desirable string vibrations.

Everyone knows how easily electric guitar and bass pickups can "find" hums and buzzes. The fast fix is simply to re-position the instrument to minimize noise reception, demonstrating how directional electromagnetic fields can be. Power-related noises radiate from cabling and power transformers; more noise is radiated as power consumption increases.

Induction is the process of radiating or receiving electro-magnetic waves. We are still very much in the age of "Wireless." Inductors consist of a coil of wire that can be wrapped around air, a piece of iron or a magnetized pole piece. Air-core and iron-core inductors are used to create complex filters for Equalizers - such as Pultec and subsequent clones - as well as passive crossover networks for loudspeakers. Power and Audio transformers also fall into this category.

Add magnetism to the equation and you get a dynamic microphone (a very small generator), a loudspeaker, a phonograph pick-up, a tape head and, you guessed it, a guitar pick-up. These are all Transducers. This month, the quest for better guitar sounds, sans noise. Since high impedance instrument pickups are cable-sensitive, exploring the interface between axe and amp should open some eyes and ears. Plus, a pair of tips that minimizing hiss in amplifier circuitry.

Fig. 1A pickup consists of a permanent magnet, a coil of wire (the bobbin) and a magnetically conductive pole piece (in most cases, one for each string). The guitar string is primarily steel, a ferro-magnetic substance, the heavier strings have an additional nickel winding. The movement of the string within the magnetic field changes the flux in the coil, generating an AC voltage. Congratulations, you have now been Inducted!

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Related Keywords:Resistance, Impedance, Gain, noise, hum, buzz, hiss, radio station, electric guitar, bass pickups, electromagnetic fields


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