Inductance for the non-technical and a question

[ShannonH]

Hi All!
It's been a while since I have posted, as I am only making pickups for a few friends and myself these days. I thought I'd share this:

Factors Affecting Inductance : Inductors - Electronics Textbook

I have been on something of a quest to understand inductance. I had read here somewhere that the insulation on the wire we use has some inductance, in descending order Poly, enamel, and formvar. This spurred on a great deal of thought as to how modifying inductance might change tone. In short, the more inductance, the "fatter" or fuller the sound, and metals that are magnetically conducive increase the inductivity of a coil.

This explains a ton about why a Dearmond/Kay pickup with a weak ferrite magnet and a steel base plate sounds any good at all, or why an "air" coil, like a Burns, can generate any volume.

Further the width of a coil also effects inductance. A simple illustration is how a Jazzmaster or P-90 pickup, although single coil, sounds big like a humbucker, but a strat sized coil wound like a P-90 still sounds mostly like a strat ( some increased inductance with screws and keeper bars.)

With the big boys listing so many pickups in the 14 to 16 k range, I was asking myself, "What differentiates these tonally when the readings are not so different?" This is especially true of the Dimarzio pickups. The key there is the Patent number. Dimarzio uses it's virtual vintage on many pickups, and thus achieve lower output, big sounding pickups that clean up pretty well.

There are many ways to "add some metal" without using dimarzio's techniques, and get that bigger tone, especially if you are fabricating some parts anyway.

I did have one question for anyone who might have tried increasing inductance by adding steel to the core: Does the steel have to touch the magnet, or does its proximity to the magnetic field suffice?

Just wanted to contribute to the place that helped me so much in the past. This is by no means comprehensive, but just a pointer. Any corrections or expansions on content welcome. Peace!

Shannon

[Mike Sulzer]

The only effect that the insulation has on the inductance is from the thickness of the insulation affecting the spacing of the turns.

By the way, the equation for inductance from your text following this sentence "An approximation of inductance for any coil of wire can be found with this formula:" is nonsense. The mu increases the inductance linearly only in coils with very low leakage flux, toroids or C-type. It does not apply to the open core shown in the figure. For short open cores such as pickup slugs, it is impossible to increase the inductance more than a few times over air core. This is why air core pickups, or ones using neo magnets as cores work OK. There just is not that much difference in inductance and signal output from the cores. It can be crucial to the sound, but the numbers are not that big.

[ShannonH]

interesting...

The only effect that the insulation has on the inductance is from the thickness of the insulation affecting the spacing of the turns.
....
For short open cores such as pickup slugs, it is impossible to increase the inductance more than a few times over air core. This is why air core pickups, or ones using neo magnets as cores work OK. There just is not that much difference in inductance and signal output from the cores. It can be crucial to the sound, but the numbers are not that big.[/COLOR][/FONT]

Thanks for the clarification. It hard to find anyone who can talk about inductance in pickup design without going into formulas. I really approach this as an art.

What about the assertions that increased inductance give a "bigger" sound? I hear this myself, but others simply say it isn't so. Thanks again!

Shannon

[Bradley Perry]

I did have one question for anyone who might have tried increasing inductance by adding steel to the core: Does the steel have to touch the magnet, or does its proximity to the magnetic field suffice?

I add steel to humbuckers I make with Alnico rods. I like the results I get from increasing the inductance without winding the pickup hotter. It doesn't have to touch the magnets directly, but the location will change the magnetic field's direction as well as how much inductance it adds. I've used both iron bars where in a humbucker where the magnets and wood/plastic spacers normally go, and also I'll sometimes use thicker and longer base plate screws than the traditional #1 or #2 screws...I'll use #8 or #10.

[ShannonH]

I've used both iron bars where in a humbucker where the magnets and wood/plastic spacers normally go, and also I'll sometimes use thicker and longer base plate screws than the traditional #1 or #2 screws...I'll use #8 or #10.

Cool! I'm considering adding mild steel rods between the magnets on rod humbuckers as well, but they would not touch any magnets.