Estimate Coil Inductance from certain parameters

[alexirae]

Hi guys,

I was wondering if there is a way to estimate inductance based on the data provided for example from salvarsan calculations:

Coil Estimator

For example, I could expect using the settings of "Strat 1967" bobbin style to get some sort of inductance between 2.0 and 2.4, but I don't know if this is such a complex parameter to calculate with just a simple formula not knowing capacitance nor resonant frequency.

I was investigating about multi-layer capacitance formulas and that kind of subjects but with not success for now, the majority of the formulas assume that you have a cylindrical shape, that makes things even more complicated.

Does anyone here knows more about the subject?

Thanks!

[bbsailor]

Hi guys,

I was wondering if there is a way to estimate inductance based on the data provided for example from salvarsan calculations:

Coil Estimator

For example, I could expect using the settings of "Strat 1967" bobbin style to get some sort of inductance between 2.0 and 2.4, but I don't know if this is such a complex parameter to calculate with just a simple formula not knowing capacitance nor resonant frequency.

I was investigating about multi-layer capacitance formulas and that kind of subjects but with not success for now, the majority of the formulas assume that you have a cylindrical shape, that makes things even more complicated.

Does anyone here knows more about the subject?

Thanks!

See this link for information about typical pickup types and induction. Bill Lawrence

The inductance is a function of coil turns, the influence of the core material and nearby metal such as plates under a telecaster bridge pickup that boosts the inductance slightly as well as focus the magnetic path. As theory goes, when you double the coil turns the the inductance goes up by the square of that turn increase or 4x, in this example. Humbuckers are the sum of the two individual coils in series plus a very little extra for the slight mutual induction between the coils.

The real issue is the environment that the passive pickups see. All coil winding capacitance, pickup lead capacitance and guitar cable capacitance work together to shape the resonant frequency and height of the pickup resonant frequency based on it's inductance. Loading of the amp input impedance along with the volume and tone controls affect lower inductance pickups less and affect higher inductance pickups more. However, good or bad sounding is subjective and in the ear of the beholder! Theory just tells you what you can expect to happen when you change any of the pickup variables or the pickup environment variables.

I hope this helps.

Joseph J. Rogowski

P.S. Look at this MEF thread for more relevant information: http://music-electronics-forum.com/t40202/

[alexirae]

Thanks for the detailed info bbsailor!

With the things you described you left me wondering about on what degree the polepieces material could affect the final inductance of the pickup.

For example, let's assume that we made a "Strat 1967" bobbin style with Alnico 5 polepieces and the measured inductance @ 1KHz was 2.2H, what would be the inductance of the same pickup using Alnico 2 or 3?, what if we use ferrous steel polepieces with an Alnico 5 magnet at the bottom? Will the inductance be affected by how much charge the polepieces have?

Beside this, and regarding inductance, I thought that there was some kind of formula that could describe the relationship between the Inductance/Number of Turns/Wire type, etc, and I found this:
Factors Affecting Inductance : Inductors - Electronics Textbook

But doesn't seem to apply properly to guitar pickups I guess because it is not taking in to account the multi-layering of the coil.

Any other extra info about this would be appreciated!

Thanks a lot!

[bbsailor]

Thanks for the detailed info bbsailor!

With the things you described you left me wondering about on what degree the polepieces material could affect the final inductance of the pickup.

For example, let's assume that we made a "Strat 1967" bobbin style with Alnico 5 polepieces and the measured inductance @ 1KHz was 2.2H, what would be the inductance of the same pickup using Alnico 2 or 3?, what if we use ferrous steel polepieces with an Alnico 5 magnet at the bottom? Will the inductance be affected by how much charge the polepieces have?

Beside this, and regarding inductance, I thought that there was some kind of formula that could describe the relationship between the Inductance/Number of Turns/Wire type, etc, and I found this:
Factors Affecting Inductance : Inductors - Electronics Textbook

But doesn't seem to apply properly to guitar pickups I guess because it is not taking in to account the multi-layering of the coil.

Any other extra info about this would be appreciated!

Thanks a lot!

Search this forum for "Extech LCR Meter" or "Extech 380193" and read about it's recommended use for measuring guitar pickups but at 120Hz. The reason for this is to keep the test frequency well away from the effects of the pickup's natural resonance and the eddy currents generated in metal cores at the 1KHz measurement frequency that increase the measurement error.

Your reference only shows single layer coils for the sake of ease of illustrating the points that are being made about: 1. Number of Turns, 2. Coil Area, 3. Coil Length, 4. Core Material, but these things also apply to muti-layer pickup coils. Calcualting inductance only yields an approximate value unaffected by resonance and eddy currents. However, with a baseline measurement with an Extech LCR meter you can pretty well estimate the effect of changing coil turns by squaring the turns difference. Assume that an 8000 turn Strat pickup measures at a 2H baseline value. Now, lets add 5 percent more turns for a total of 8400 turns. The calculated inductance will be 1.05 X 1.05 more or 1.1025 X 2H or 2.205H. Just square the additional turns and multiply by the baseline value. If you increased the turns by 10 percent then it would be 1.1 X 1.1 or 1.21 more X 2H or 2.42H.

I hope this example answers your question.

Each of those 4 inductance factors applies to guitar pickups as different styles have a different footprint and/or pickup height, coil area, and core type, and number of turns, for example the Telecaster neck pickup vs the P90 pickup.

Different magnets will also affect the tone. Search this forum for many posts about this topic. It is best to measure your pickup baseline with a known bobbin shape and core material as there will be less variables when calculating the effect of adding more coil turns. There is one variable that will have a slight effect is the tightness and/or compactness of the winding. More scatter winding puts more air between the winds and adds less inductance than a tight machine wound coil where the wire is very close together.

There is a wealth of pickup knowledge on this forum so use the search function or scan the thread topics.

Joseph J. Rogowski