WTF is a Guitar Signal?Posted: April 23, 2012
A guitar’s circuit is a relativity easy one, basically it has no chance of launching itself to the moon. (What do rocket scientist say when they want to say something isn’t hard? It’s not like we’re trying to talk to women. -Jim Gaffigan) Just a handful of components and a basic understanding of how they work will arm you with enough knowledge to start designing your own guitar circuits and modifications. In Part 1 I will attempt to explain what the signal is and how a passive pickup equipped guitar (no batteries) produces it.
When we pluck a string on our guitars an electrical signal is generated through the phenomenon known as electromagnetic induction. Electromagnetic induction is the production of an electrical current in a conductor within close proximity of a changing magnetic field.
As the string vibrates it disrupts the magnetic field made by the magnetic pole pieces producing an electrical current that the copper coil “picks up”. When installed into a closed circuit like in our guitar, this current becomes the guitar’s signal that can be manipulated by adding potentiometers, capacitors, and switches before making its way to the amplifier. If you are into physics you will most likely know the name Michael Faraday, he is most commonly associated with the discovery of electromagnetic induction. If you are interested in the complete physics behind electromagnetic induction there are lots of resources about him and his findings on the web. As a guitarist, or a person wanting enough knowledge to impress most people after a couple of pints, the information I present to you should do.
The electrical energy that is produced by a pickup is alternating current (AC). You are most likely familiar with AC if you have ever turned on a coffee pot, watched TV, or have accidentally driven a nail into the wiring of your house while trying to hang a picture. The electrical signal produced by our guitar’s pickups is just like the electricity that comes out of the outlets in our house, just much smaller.
The green line, or sine wave, is a visual of what an AC signal looks like. It starts at 0, goes positive, goes negative and back to zero, over and over until the signal is terminated. Each time it does this 0 to maximum to minimum back to 0 is called a cycle. Cycles are typically represented in Hertz (Hz) which is the number of cycles per second. When we tune our guitars to A440, we are tuning to a signal that is making 440 cycles per second, or a 440Hz signal.
Relating this image of AC to our guitars, we can think of the sine wave as a guitar string. When the string is idle it is at 0, not disrupting the magnetic field therefore not producing an AC current. When we pluck the string it vibrates, in essence a string’s vibration is a back and forth motion. If we play the A note found on the first string fifth fret you would see 440 complete cycles of the string’s vibration per second producing an A440 note. As it goes in one direction the sine wave goes + and when it travels in the reverse direction the sine wave goes -. The amplitude is the strength of the signal, the harder we pluck the string, the further the sine wave will travel into + and - territory. As the string starts to lose sustain the amplitude starts to shrink until eventually reaching 0 or silence.
In a future post I will talk about pickup specifications, components, and what method I found best for finding the perfect pickup. Until then enjoy this video showing the making of a Seymour Duncan custom shop pickup.
Other related resources.