Inductance

[Paulkstadden]

What affects inductance? I read on Chris Kinman's site that the reason the old Duncan stacks sounded terrible was due to low inductance. The old Strat pickups had something like 2.3 Henrys, but A Duncan stack had only 1.8 Henrys. Does it have to do with how the coil is wound, what guage wire is used, what type of magnet, whether it's a humbucker or single coil, or what?

[Possum]

ducktance....

It has alot to do with various things, not just one thing. the taller a coil is the lower the inductance will be, the fatter the wire it will be lower, the more metal that is in contact with or near the coil the higher it will be. But to confuse things alot of time when you add more metal the inductance goes DOWN not up but your tone gets darker. For instance if you read the inductance of a P90 before you slap a brass baseplate on the bottom it will X amount but when the base plate goes on the inductance will drop, but you will lose some treble from the baseplate being there due to eddy currents. confusing eh?

AC resistance is a better guide to how a coil will sound than inductance is for me. A good LCR meter is real useful for making repeatable pickups that all sound the same or as close as you can get without buying a perfect winding computer coil winder.

[Paulkstadden]

Huh, yes, that is confusing! I'm the kind of person that likes simple, "if you add this, this will happen, if you remove that, there will be an increase in those" kind of formulas. Still, I thank you, that is excellent info. So, then, I guess my next question would be, how does one fight eddy currents? Bill Lawrence's site makes mention of eddy currents and what they are, but how can they be controlled? Can I assume eddy currents are a bad thing?

By the way, when you say AC resistance, do you mean kiliohms? As in, "my hot pickup reads 16k ohms"?

[David Schwab]

I don't think those old Duncans sounded bad at all. I had a set in a Strat. They sounded good to me! Duncan also uses a very different design than Kinman/DiMarzio. Duncan's magnets ran all the way though both bobbins, and in the case of the hot stack, was in-between the upper and lower steel rails. DiMarzio doesn't have lower magnets or cores in the bottom coil. DiMarzio and Kinman have magnetic shields between the coils.

Kinman's design adds a bunch of metal to the bottom coil. This raises the inductance. This is the same as cores in transformers. Kinman uses laminated core material (as in transformers) to avoid problems with eddy currents. His bottom bobbin is made from this material. Laminated steel is thin sheets separated by an insulator. This sheets have less eddy currents than thick sheets.

Bartolini once made humbuckers with laminated steel blades. Normally having a thick steel blades will muddy the tone. Inductance is not a bad thing in the case of pole pieces. Pickups work on the principle of magnetic inductance. But the combination of high inductance with eddy currents shunts the highs. The Bartolini pickups had high inductance, which produced a string midrange, but avoided the eddy current loss. This is also what Kinman is doing.

Eddy currents are electrical currents that swirl (in eddies) on the surface of a conductor in the presence of a magnetic field. These currents produce their own magnetic field that opposes the field that created them. In pickups they tend to shunt highs.

The thing to keep in mind is that you only need to match the inductance of a stock Strat pickups if you are trying to sound like a stock Strat pickup. Some designs use lower inductance, and some use higher.

[Arthur B.]

It has alot to do with various things, not just one thing. the taller a coil is the lower the inductance will be, the fatter the wire it will be lower, the more metal that is in contact with or near the coil the higher it will be. But to confuse things alot of time when you add more metal the inductance goes DOWN not up but your tone gets darker. For instance if you read the inductance of a P90 before you slap a brass baseplate on the bottom it will X amount but when the base plate goes on the inductance will drop, but you will lose some treble from the baseplate being there due to eddy currents. confusing eh?

Wikipedia has a section on Inductance with some formulas in it. You'll have to look up the constants, though.

[Paulkstadden]

Excellent info. Kinman's site didn't make mention of how he raised inductance. What was the laminated core material he used? Laminated steel like the Bartolini you mentioned? Was it the fact that the steel was laminated that helped in fighting eddy currents?(By the way, I don't know what those old Duncan Stacks sound like, I was just quoting Kinman! )

[David Schwab]

Excellent info. Kinman's site didn't make mention of how he raised inductance.

Sure he does! Right on this page

Here are some pictures of what makes my Tele models so special. Note the innovative 100% steel laminated bobbin (H-Core) in pic #1, it's made from 150 'H' shaped steel plates. These 150 plates are not allowed to touch each other. This is a world first never before seen in guitar pickups. It took me 3 years of exhaustive R&D to figure out how to manufacture this special bobbin. Of course it's Patented. This innovative bobbin is the secret of how I was able to create noiseless, authentic sounding Tele pickups that retain the appearance of the originals, with Alnico magnets and the string wrap. Anyone wondering about the value for money aspect of these products will no doubt develop a deeper appreciation after seeing this; you won't find too many people who would like to make two of these for the price I ask.

And read these patents applications:

20060112816

20020083819

[Paulkstadden]

Ah! I didn't see that. I was looking in his personal history, which is where he discusses his discovery of inductance. Thanks for the patent info!