42 vs 43 questions/ winding pattern differences

[rosssurf]

I am kind new at this. I am interested in winding my own single coil pickups. I recently rewound a Fender Texas Special bridge w 42 guage wire to read 7.20 on my ohm meter. ?? is this the same as DC resistance?

I know there are many factors that create tone and no winding can be EXACTY duplicated but I have a few question to ask.

If one has a pickup whose windings are rounded..meaning less wire near the bobbins and more in the center...and with all other thing being as close to equall as possibe..another one exactly the same ohm reading and everything but the wire is wound more like an hourglass...meaning more wire close to the bobbins and much less in the center....are there some generalizations that can be made about the tonal differences?

Also what if I took the same Fender TS pickup I wound to 7.2 w/ 42 guage wire and wound it to 7.2 with thicker, or lighter wire...what generalizations can be made about thier sonic differences?

Maybe these are dumb questions but I would like to learn..

Is there any link someone could provide to a web page or old post that answers these questions?

Thanks
Ross - Baltimore

[salvarsan]

I am kind new at this. I am interested in winding my own single coil pickups. I recently rewound a Fender Texas Special bridge w 42 guage wire to read 7.20 on my ohm meter. ?? is this the same as DC resistance?

Yes. It would be 7200 ohms or 7.2 k-ohms.

Also what if I took the same Fender TS pickup I wound to 7.2 w/ 42 guage wire and wound it to 7.2 with thicker, or lighter wire...what generalizations can be made about thier sonic differences?

7.2k of #42 on a Strat bobbin is around 9000 winds, but only 7600 winds using #43.

The #43-wound pickup would sound brighter. Generally, more winds = more bass, more output.


You can estimate winds from DC resistance and bobbin size using
http://www.salvarsan.org/pickups/Coil_Estimator03.html

-drh

[David Schwab]

Generally, more winds = more bass, more output.

Now I have a question I was thinking about one day... if you wind 8,000 turns on two identical bobbins, one with 42, and then another with 43, obviously the thinner wire will have a higher resistance, and the coil will be smaller. My experience has been that it will have less low end and a more pronounced midrange. The heavier wire will be rounder sounding.

But what exactly accounts for this? Coil size? And does the higher resistance figure into the difference tone of the two coils that are wound with the same number of turns?

[Seth Leigh]

I believe it would have to be the resistance. I'm no expert in any of this at all, but I do know that an RL circuit will act as a filter to alternating current, and the resistance and inductance both factor into establishing the cutoff frequency and whatnot. With the same number of turns, I think the inductance would be the same, but the resistance of the two wire gauges would change, therefore the frequency response of the filter would have to be different. I'm sure some guru will chime in with more on that, but I think this is probably how it goes.

[David Schwab]

Yeah, I figure at some point Dan or Joe or Mike will step in with some math that I'm no longer in the mood to deal with!

Resistance might be part of it, but even if you buffer the coil you still hear quite a difference.

I've been messing with thin wire lately, mostly from working on some dual rail Jazz bass pickups. 43 and 44 wire had way too much midrange in that small aperture, even though they sound good with larger aperture pickups.

I decided I liked the tone of the 42 wire better, though it made the coils larger. I wish I had some 41 to try, but I do have some 40.

[Mike Sulzer]

I believe it would have to be the resistance. I'm no expert in any of this at all, but I do know that an RL circuit will act as a filter to alternating current, and the resistance and inductance both factor into establishing the cutoff frequency and whatnot. With the same number of turns, I think the inductance would be the same, but the resistance of the two wire gauges would change, therefore the frequency response of the filter would have to be different. I'm sure some guru will chime in with more on that, but I think this is probably how it goes.

The R and the L do not have a lot of effect alone; when you consider the C (pickup and cable capacitance) that you get some more effect from the coil resistance. The RLC forms a resonant circuit, not very high in Q, but nonetheless it is resonant. If you make the series R larger (smaller wire) this damps the resonance a bit, lowering the height of the resonant peak. Not a large effect with #43 versus #42, but it is there.

Also, the L should be a bit different when using #43 instead of #42. You have changed the shape of the coil. With an air core coil, you could compute this effect easily. With a closed high permeability core (like a toroid or frame transformer), the effect would be extremely small. With short open cores as used in a pickup, the effect is more complicated to compute, but maybe you could measure it.

[Bruce Johnson]

I have a similar question to David's....looking for a general understanding of how design parameters affect the tone.

If you kept the wire gauge the same, and the number of turns the same, what would be the tone difference between a coil that is larger in diameter and lower in height, versus one that is smaller in diameter and taller? Obviously, the short/wide coil would have higher resistance, because it would take more feet of wire to get the same number of turns. So does this mean that it would have less bass and more midrange than the tall/narrow coil? Is this primarily because of the resistance effect on the RL circuit, or position of the coil turns in relation to the magnetic field? I'm assuming the same magnets and magnetic field shape for both.

As a related thought experiment, suppose you kept the wire gauge the same, but varied the number of turns to keep the DC resistance the same? In this case, the short/wide coil would have fewer turns than the tall/narrow coil. Again, assuming that the magnets and field are the same, what would the tone difference be between these two coil designs? Would the fewer turns of the short/wide coil mean lower output and less high end?

Most of the discussions I've read about comparing height/diameter of pickups have been about the overall pickup, which means that the height of the magnets and the resulting difference in field strength and shape are part of the tonal change.

I'm trying to understand specifically about the coil geometry itself.

[David Schwab]

If you kept the wire gauge the same, and the number of turns the same, what would be the tone difference between a coil that is larger in diameter and lower in height, versus one that is smaller in diameter and taller?

There are two well known examples of those... the P Bass has a wide squat coil, and the Jazz bass has a tall narrow coil. More examples would be comparing a Strat pickup to a Jazzmaster.

Now the question is, does the wide coil sound that way because it's sensing a wider aperture of the string, or because the outer winds are father from the core, or some combination of the two?

[Bruce Johnson]

Yeah, that's what I'm getting at. And the bigger factor in comparing P-bass vs J-bass pickup tone is probably in the magnets and field shape.

Have any of us really isolated out the coil geometry as a test?

[Mike Sulzer]

Yeah, that's what I'm getting at. And the bigger factor in comparing P-bass vs J-bass pickup tone is probably in the magnets and field shape.

Have any of us really isolated out the coil geometry as a test?

Each turn contributes a voltage depending upon the changing flux integrated over the area of the turn. The pole piece tends to keep the flux inside it with only some outside, so you do not expect to sense more of the string with a large loop.

Here is a question that can help in understanding this:

Suppose we have a pole piece under each string, and each pole piece has its own coil, all electrical and magnetic polarities the same. Consider the signal in the number 4 coil from the number 3 string. Does it have the same or opposite sign as the signal from the number 3 string in the number 3 coil? This tells you something about the effect of sensing flux changes far from the core.

[Possum]

.

Another factor to consider with same amount of turns and different wire, the thinner wire will make a smaller coil, that is more directly in the "hot zone" where the flux is the densest, so the whole coil is in that stuff, where as a larger coil of larger wire, the outer winds are out where the flux is weaker. You can't really measure this but is a very active thing that is affecting how the pickup sounds and reacts....

[Robert M. Martinelli]

Now I have a question I was thinking about one day... if you wind 8,000 turns on two identical bobbins, one with 42, and then another with 43, obviously the thinner wire will have a higher resistance, and the coil will be smaller. My experience has been that it will have less low end and a more pronounced midrange. The heavier wire will be rounder sounding.

But what exactly accounts for this? Coil size? And does the higher resistance figure into the difference tone of the two coils that are wound with the same number of turns?

Hi David,
IMHO the answer lies in the fact that DC resistance ( which also accounts for the "real" part of impedance ) influences the "Q" factor too. The formula is Q=(1/R)*Sqrroot(L/C), so, the increased DC resistance makes for a smaller "Q" factor, which broadens the pickup's bandwidth, because Bw=Fo/Q where Fo is the resonant peak. The number of turns being the same, I also expect a slightly lower stray capacitance ( which should move the resonant peak to the high side ), but not enough to compensate for the "Q" reduction due to the increased R in the first formula. I guess this is why you found more pronounced mids ( reduced "Q ) and less low end ( higher resonant peak ) with 43.

HTH

Best regards

Bob

[Bruce Johnson]

That's the heart of my question: If you keep everything else the same, but arrange the wire differently around the magnetic field, how does that affect the tone? How does a tall narrow coil, where the wire is in close around the magnet, compare to a short wide coil? The short wide coil will have part of its turns farther out from the highest flux areas around the center of the magnet. But the tall narrow coil may have some of its turns out of the highest flux areas out at the two polarized ends.

If you started with a tall narrow coil, and then went to a shorter, wider coil with the same resistance and number of turns (by using a larger wire), what would it do? I can see how the signal level might go down, because of the turns being farther out in the flux field, but would it change the frequency curve?

[Robert M. Martinelli]

Just a reminder of the basic equations of our interest:

F0 (resonant peak ) = 1/(2Pi*(Sqrroot(L/C))), where L is the coil's overall inductance ( more on this later ) and C is the coil's stray capacitance.

Note that the coil's DC resistance does not affect the resonant peak value.

Q ( Quality ) factor = (1/R)*(Sqrroot(L/C), where R is the DC resistance, L and C are the same as above.

Bw ( Bandwidth ) = F0/Q ( good approximation ), where F0 is the resonant peak and Q is the Quality factor.

By far, the most significant of all the above factor is L ( Inductance ), expressed by the formula :

L= ((u0*um*(N^2)*A)/l

Where u0 is the air's magnetic permeability, um is the magnetic core's material permeability, N^2 is the number of turns squared, A is the core's area and l is the core's lenght ( height in our case ).

To answer your question using the above math, a "flatter" core with the same number of turns should have a greater inductance because l ( the equation's divider ) is smaller, so the resonant peak would be lower and the Q factor higher ( the pickup would be more "focused" on the frequencies close to the resonant peak. Changing from 42 to 43 while keeping the number of turns the same would increase DC resistance and bring down the Q factor some, but it's a first-order effect, while changing the number of turns would have a second-order effect on inductance ( N^2 in the formula ).

Also, it must be remembered that load ( guitar cord, amp input circuitry ) plays a very important role, so it has to be taken into account when mathematically modeling a pickup's behavior, after all the guitar/bass has to be connected to an amp, right ?

Hope this helps, and hope I've been able to make things clear enough, despite my rather poor English

Best regards

Bob

[Mike Sulzer]

Another factor to consider with same amount of turns and different wire, the thinner wire will make a smaller coil, that is more directly in the "hot zone" where the flux is the densest, so the whole coil is in that stuff, where as a larger coil of larger wire, the outer winds are out where the flux is weaker. You can't really measure this but is a very active thing that is affecting how the pickup sounds and reacts....

Yes, and remember that it is the whole flux passing through a loop that matters so a larger turn sees the flux that a smaller one sees, plus some additional flux. But this additional flux far from the core is not what you might expect. Field lines are closed, so the flux from the vibrating string that passes down through the core must loop around and return to the string. Most of it passes well outside the coil and is not a factor. But some passes through the coil and these field lines point in the opposite direction as the ones that go through the core. (Follow a line down through the core and then back up outside, always keeping the little arrow pointing along the line.)

So the flux outside the core slightly reduces the total net flux through a large loop, and you get a bit less output from a larger loop than a smaller one.

This is the lesson of the question above: if you have individual coils, the leakage from the signal of one string into another coil has the opposite sign. You can measure this; it really does work this way.

Of course some pickups do not have cores; that is, no high permeability rod or blade. An example is a pickup using Neo rod magnets as the "cores". Neo has a permeability only 4% above a vacuum, and so it does not affect field lines very much. Of course, it still only magnetizes a short section of string, but it is still a different case.