* This series of ‘theory Stuff’ posts is meant to introduce some of the basic science behind electronics. I’m going to avoid all but the simplest of maths. Just to point out, in simplifying, I’m basically telling some small fibs, but I’m doing it for the best of reasons: to help you grasp the concept.*
Let’s start with voltage.
The best way to think of voltage is electrical pressure pushing (or pulling) the electrons in one direction or another.
DC (direct current) means that electricity flows in one direction only, from voltage source to ground 1. We use DC to power guitar effects, usually 9V and sometimes 12V and 18V.
AC (alternating current) means that the voltage swings positive and negative like this sine wave.
Guitar signals are AC voltages, just a wee bit more complex than the simple sine wave above. We’ll look at those later, but we still need our sine wave.
Humans can hear between 20Hz (Hertz) and 20KHz (20 KiloHertz or 20,000Hz). 1Hz means one cycle per second. That’s one positive upswing, and one downswing before returning to the centre, completing the cycle, like in the picture above.
20Hz is 20 of these cycles per second, 20KHz is 20,000 per second. Higher frequencies mean higher pitches. A is 440Hz, the next octave above is 880Hz, the octave below is… … yup, 220Hz.
As I mentioned earlier, guitar signals are far more complex and beautiful than sine waves because they consist of the frequency of the fundamental note you’re playing and many harmonics above the fundamental.
There’s a good explanation from about half way down this page on allaboutcircuits.com detailing what happens, I’m not going to repeat it here, if you continue reading to the next page, you’ll see these images showing what happens to a sine wave as you add the harmonics, like this.
The more harmonics you add, the more complex the waveform becomes.
Pickups are wonderful things that convert string movement into a small AC voltage. Pickups are inductors. they have a magnetic core wrapped in copper wire. By the marvels of electromagnetism the up and down motion of the string creates a back and forth movement of electrons in the copper coil which travels down the lead and into some pedals (hopefully loads and loads of pedals).
All of this fantastic science causes a thing called impedance in our guitar signal, which leads us to Clever Stuff 2 – Get outta my way! Impedance, where we’ll step it up a notch.
fundamentals and harmonics
allaboutcircuits.com is a great website for all the fundamentals of electronics. I highly recommend reading as much as you can. It’s all free too.
1 This is the first lie. What I have described is called ‘conventional flow’. That’s the model used by most people in electronics. Electrons actually flow the other way, from ground to the more positive voltage source. We have Benjamin Franklin to thank for that, but he was such a dude that I think we can let it go. It’s probably too late now anyway and it doesn’t actually make any difference mathematically.
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