Inductance?

[polifemo]

So, I understand how different wires/how many turns on a coil, affect the resistance reading.
I also understand how different magnet types affect the tone of a pickup, but what I (yet) do not understand is how inductance works, how it is controlled and what affect it has on the sound of a pickup...

I´m eager to learn

[Chris of Arabia]

Very simply, an inductor is a frequency sensitive component that works the opposite way round to a capacitor. At DC or very low AC frequencies, it looks electrically like a short circuit. As frequency increases though, it's resistance gradually increases, until it becomes a resistor of infinite value. Picking the right value of inductor allows you to use them as a low pass filter and so 'tune' a circuit.

[polifemo]

So, when winding a pickup, how does one control the inductance and which component in the pickup is responsible for the actual inductance?

[Chris of Arabia]

It's down to the coil of wire itself. How many turns, gauge of wire. If you add a ferrite or magnet, your inductance should go up, same with more turns of wire.

[King IzzO)))]

The way I understand it is the more metal you have around the circuit, the higher the inductance will be.

Copper shielding around the coils = higher inductance.
Using a keeper bar vs. no keeper = higher inductance.
Alnico magnet vs ceramic magnet = higher inductance.
Large poles/thick blades vs. small/thin blades = higher inductance, etc.

Higher inductance = warmer/darker sound.

Dimarzio "virtual vintage" is just hidden poles in the bobbin to raise the inductance.

[Chris of Arabia]

Higher inductance = warmer/darker sound.

Not necessarily. It depends on how the inductance is presented in the circuit.

[King IzzO)))]

Not necessarily. It depends on how the inductance is presented in the circuit.

It is generally a safe assumption applied to guitar pickups though, right?

[Chris of Arabia]

To be honest, I'd actually need to think about it for a few minutes and it's gone midnight already. The grey cells are just a little sleepy right now.

[polifemo]

Thanks guys, I´m starting to get this now :-)

I quite often order custom pickups from small winders, and the more I know about the tech stuff, the better the chances of getting "the right pickup"!

[Dr. Vegetable]

Warning - dense sciencey stuff follows...

There are three elemental "passive" electronic components: the resistor, the capacitor, and the inductor. Inductance and capacitance are similar concepts in electronics that can be thought of as "frequency-dependent resistance." A capacitor behaves like a resistor at low frequencies, and behaves like a straight piece of wire at high frequencies. An inductor acts like a resistor at high frequencies, and behaves like a straight piece of wire at low frequencies. So these components can be used to impede certain frequencies in our signal while allowing others to pass through unmolested.

Purely resistive circuits (those containing no caps or coils) can be understood using Ohm's Law: V = I*R, which determines the relationship between voltage applied to the circuit and current that flows through it. Because power is equal to V * I, we get more power through a circuit when both V and I get larger. So a low R value will draw more power than a high R value if the same voltage is applied to the circuit.

But once we add capacitors or inductors into the circuit, things get a bit more complicated. (And since we live in the real world, no circuit is purely resistive.) Capacitors oppose sudden changes to voltage across their terminals, and inductors oppose sudden current changes through them. The bigger the capacitance/inductance value (measured in units of Farads or Henrys), the greater the opposition to change. This means that the circuit's behavior depends on how fast the current or voltage is changing in the electrical signal. The higher the frequency of the signal, the faster V and I are changing back and forth, and so the capacitor and inductor will oppose/suppress high frequency signals, but will allow low frequency signals to pass through them unimpeded. This is how filter circuits are built.

Electrical engineers (and physicists) have developed the concept of Reactance to help predict how a circuit will react to signals at different frequencies. You can think of Reactance as "resistance as a function of frequency." In other words, if you have a signal of a single pure frequency passing through, you can determine the Reactance it will meet in the circuit to determine the power consumption of the circuit still using Ohm's Law.

Again, in the real world, few interesting signals consist of a single frequency. A chord is, by definition, a blend of notes at different frequencies. But even a single note plucked on a single string contains many different frequency harmonics. The tone knob on your guitar is a variable filter circuit that can be adjusted to allow more or less of the high frequency harmonics to pass through.

So inductance is very similar to the concept of capacitance. They are really two different names for the same concept, just as "hot" and "cold" are different names for the concept of temperature. The inductance value of a coil (measured in Henrys) will increase as you add more coils of wire. More coils (higher inductance) in a guitar pickup will tend to make it more sensitive to string motion. But when considered in the context of the total circuit, it can also alter the frequency response of the guitar - what we hear as "bright" or "dark."

This is the fifty-cent tour. For more information, please take a graduate-level electronics course at your nearest university.

[robrob2]

That was a fantastic summary of basic electronic theory Dr Vegatable, thanks for posting.