Resistance and Conductivity in Guitars
So, we talked about how a pickup actually works: A guitar string vibrates in a magnetic field and induces an electrical current in the pickup coil. Brilliant. Physics, baby!
That electrical current is what makes the wonderful noise of our instrument. But what is that current?
Remember school science class? Atoms have a nucleus and a number of electrons orbiting about it? An electrical current is essentially a ‘train’ of charged electrons that flows through a material. The electrons flow from an atom to the next one along, and so on down the line.
In our case, those materials that make up that line are the pickup coil wire, the hook-up wires, the electronic components in the guitar, the wire in the guitar lead, and the components in your amp.
Some materials are better than others at conducting this flow of electrons—the electrons can move more freely in them. A material that allows easier electron movement—and therefore easier current flow—is called a conductor.
Many metals make good conductors of electricity and one of the best for everyday use is copper. There’s a reason that most of the electrical wiring in your house is copper and we also use copper wire extensively in electric guitars and basses.
However, let’s leave that for now. Let’s look at the other side. Let’s look at resistance.
While some materials make it easy for electrons to skip happily down the line, others can bounce and jostle them about as they move, making their path more arduous. A material that makes it difficult for those electrons to move through it is said to ‘resist’ current flow.
We can make use of this effect to control things.
A resistor, as the name suggests, is an electronic device whose job is to resist the flow of electric current. It essentially makes it harder for current to pass through. The higher the resistance value of the device, the harder it is for current to pass through.
There are many, many different ‘fixed-value’ resistors available for use in electronic equipment but we’ll primarily be interested in variable resistors.
With a variable resistor, the resistance value can be altered manually—generally from zero (no resistance at all) to a top, preset, value.
In your guitar, you’ll probably find one or more of these variable resistors. They’re known as potentiometers but, for obvious reasons, we generally abbreviate this and call them pots. They’re most often used to control the instrument’s volume and tone.
A pot is not a terribly complicated device. It has three connections. In the image above you can see that the pot comprises a circular resistive track, and a wiper which moves along the track to vary the resistance.
If you measured the resistance between one end of the track and the other (or points 1 and 3 in our pot), it would equal that particular pot’s total resistance value.
However, if we measure between one end of the track and the wiper (point 1 to point 2), the resistance would vary depending on where then wiper was positioned along the track. Fully counter-clockwise the resistance should be zero and it would rise to the full value as the wiper is rotated all the way clockwise (to the other end of the track). As the wiper moves, it increases or decreases the resistance.
Got all that?
The Bottom Line
There’s a bit to take in here, I know, and it’s possible you might be wondering why I’m going on about it.
Understanding something about conductivity and resistance can be massively useful as these concepts feature strongly in guitar electronics.
A bit of knowledge of the path your juicy guitar tone travels on the way to your amp can also help make sense of things when it comes to tracking down problems and understanding one of the tools of troubleshooting: the multimeter.
More on that later, though. I’ve gone on long enough for now.
COMPLETE GUITAR WIRING
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