Measuring pickups Capacitance?

[Antigua]

Yes, and for this reason very wide loops (turns) produce near zero induced voltage. But as the voltages of all turns add up, the total EMF will not decrease by additional outer turns.

So what creates a sum of voltage: all of the flux through the loop itself, or just the flux through the wire that constitutes the loop? Lets say you have a wide area turn of wire with a little pole piece in the centered and above this large loop. Even though the wide area of the wide loop has both positive and negative flux from the pole piece passing through its wide area, the actual wire of the loop only intersects with the broad return path of the pole piece in the center. Therefore, when the pole piece moves around, it will induce a voltage that is opposite phase from what it would have been had the loop been very small. This reverse-phase voltage would not be zero. Please let me know if I'm missing something.

[Mike Sulzer]

So what creates a sum of voltage: all of the flux through the loop itself, or just the flux through the wire that constitutes the loop? Lets say you have a wide area turn of wire with a little pole piece in the centered and above this large loop. Even though the wide area of the wide loop has both positive and negative flux from the pole piece passing through its wide area, the actual wire of the loop only intersects with the broad return path of the pole piece in the center. Therefore, when the pole piece moves around, it will induce a voltage that is opposite phase from what it would have been had the loop been very small. This reverse-phase voltage would not be zero. Please let me know if I'm missing something.

All the flux through the loop. The voltage exists around the path of the wire even if the wire is not there.

[Joe Gwinn]

All the flux through the loop. The voltage exists around the path of the wire even if the wire is not there.

I'd rethink that a bit. Specifically, each turn stands alone, as does each line of flux, so the voltage in each turn is the flux change in that turn. A coil of finite size in a non-uniform field will have different amounts of flux in every turn. The closer the coil is in physical shape to a single thin turn, the less variation there will be, but pickup coils are physically pretty thick and short.

[Antigua]

All the flux through the loop. The voltage exists around the path of the wire even if the wire is not there.

You're right, total flux change would increasingly approach zero, but would not go negative if the source of flux change is over the loop boundary.

The mistake I made was thinking flux "through" the wire caused a voltage and pushed current, but it's actually flux change "beside" the wire that causes voltage and then current. And so when there's a loop, it ensures that all of the flux of a given polarity beside the wire will push the current in one particular direction, thereby doing something useful. The problem with a wide loop of say, a P-90, is that instead of a "given polarity", there are two polarities, primary and return path, and though the primary flux will always be the denser of the two, as the loop becomes wider it catch more of the return flux, coming ever closer to zero net change.

[Mike Sulzer]

I'd rethink that a bit. Specifically, each turn stands alone, as does each line of flux, so the voltage in each turn is the flux change in that turn. A coil of finite size in a non-uniform field will have different amounts of flux in every turn. The closer the coil is in physical shape to a single thin turn, the less variation there will be, but pickup coils are physically pretty thick and short.

I think given the choice of "all the flux through a loop" or just the "flux trough the wire", I answered correctly. (I realize that there are some potentially confusing cases [https://en.wikipedia.org/wiki/Farada..._of_induction] and what I wrote does not cover all possibilities, but I think it is OK for what we are discussing here.)

[Helmholtz]

The problem with a wide loop of say, a P-90, is that instead of a "given polarity", there are two polarities, primary and return path, and though the primary flux will always be the denser of the two, as the loop becomes wider it catch more of the return flux, coming ever closer to zero net change.

Zollner's results show that the outer turns of a Jazzmaster PU on average produce as much volts per turn as the most inner windings (both 1.7µV/turn) with a maximum of 2.3µV/turn somewhere in the middle of the coil (numbers are for reference, actual values depend on several variables).
The JM PU produced about twice the output of a vintage strat PU. This is mainly due to the wider and flatter coil. The flatter coil allows the majority of the turns to be closer to the strings, thus increasing efficiency. EMF yield per turn decreases strongly with distance from the strings.

This also demonstrates that the flux returning from the string is not confined within the aperture but spreads out over an area considerably wider. Consequently a coil can be made pretty wide (wider than JM and P-90 coils ) before the outer turns cease to contribute to output noticeably and merely increase L and DCR.

I can't see a "problem" with JM or P-90 shaped coils.

[Antigua]

Zollner's results show that the outer turns of a Jazzmaster PU on average produce as much volts per turn as the most inner windings (both 1.7µV/turn) with a maximum of 2.3µV/turn somewhere in the middle of the coil (numbers are for reference, actual values depend on several variables).
The JM PU produced about twice the output of a vintage strat PU. This is mainly due to the wider and flatter coil. The flatter coil allows the majority of the turns to be closer to the strings, thus increasing efficiency. EMF yield per turn decreases strongly with distance from the strings.

This also demonstrates that the flux returning from the string is not confined within the aperture but spreads out over an area considerably wider. Consequently a coil can be made pretty wide (wider than JM and P-90 coils ) before the outer turns cease to contribute to output noticeably and merely increase L and DCR.

I can't see a "problem" with JM or P-90 shaped coils.

Do you remember which resource from Zollner included the Jazzmaster pickup coil analysis? Was is somewhere in PotEG?

I think that even if the primary-path flux contribution covers a wide area of a wide coil, that it would be important to note that the harmonic make up of the flux change, as caused by the harmonically moving guitar string, would be based on a smaller aperture, one that is closer in size to the pole piece.

[Helmholtz]

Do you remember which resource from Zollner included the Jazzmaster pickup coil analysis? Was is somewhere in PotEG?

This information is contained in the coloured illustrations of page 5-31, German book version of PotEG.

I think that even if the primary-path flux contribution covers a wide area of a wide coil, that it would be important to note that the harmonic make up of the flux change, as caused by the harmonically moving guitar string, would be based on a smaller aperture, one that is closer in size to the pole piece.

Sorry, this sentence is too complicated for me. But sounds like pure speculation without reasoning. Aperture corresponds to the magnetized string length. It is roughly given by twice the pole diameter of a SC (as measured by Zollner). Extension of primary flux close to string must be smaller than aperture. I have not seen any evidence of a frequency-dependance of the aperture up to now.

[bbsailor]

Zollner's results show that the outer turns of a Jazzmaster PU on average produce as much volts per turn as the most inner windings (both 1.7µV/turn) with a maximum of 2.3µV/turn somewhere in the middle of the coil (numbers are for reference, actual values depend on several variables).
The JM PU produced about twice the output of a vintage strat PU. This is mainly due to the wider and flatter coil. The flatter coil allows the majority of the turns to be closer to the strings, thus increasing efficiency. EMF yield per turn decreases strongly with distance from the strings.

This also demonstrates that the flux returning from the string is not confined within the aperture but spreads out over an area considerably wider. Consequently a coil can be made pretty wide (wider than JM and P-90 coils ) before the outer turns cease to contribute to output noticeably and merely increase L and DCR.

I can't see a "problem" with JM or P-90 shaped coils.

Yes, there are many variables to consider. Jazzmaster pickups with their short magnets project a different magnetic field compared to a Stratocaster type pickup with longer magnets. Then there is increasing magnetic strength but at the expense of potentially damping the string vibration. Look at the mechanical design of a P90 type pickup. https://courses.physics.illinois.edu...eport_Sp10.pdf

Two rectangular bar type magnets with the same magnetic pole facing the metal bar which holds the string pole pieces spreads the magnetic field differently than the magnetic field in a Jazzmaster with short round magnets.

Given that the initial design of the guitar pickup was to generate enough voltage to drive a high impedance tube-based amplifier input, all early passive pickups used 5,000 to 10,000 turns of AWG 42 to AWG 44 wire with different sonic consequences. Adding more turns typically increases the output but changes the sound. The human ear is very sensitive to the initial 30 to 50 milliseconds of the pickup attack transient and when playing with other instruments allows the guitar transient to provide accents to the sound. Short wide pickups like a P90 of Jazzmaster keep more wire closer to the string up to the point where adding more wire has a diminishing return not only in output level but in length of the string that is generating voltage with some upper harmonics being out of phase with very wide pickup designs.

It all gets down to understanding the desired effect of what we do to alter the pickup design with the technical understanding that simply adding more turns to increase the output has other consequences as well. Our ears are the best test device for what sounds well while the technical analysis has evolved to better understand the variables such as:
1. coil turn numbers
2. coil shape (tall and narrow versus short and wide)
3. magnet size tall or short
4. magnet type
5. amount of ferrous metal in the pickup design
6. coil wire size, insulation dielectric
7. winding style, machine wind (tightly wound) versus hand wind (more scatter)
8. distance from strings
9. loading by passive controls
10. the effect of cable capacitance and amplifier input impedance

When you listen to an acoustic guitar with a non magnetic pickup typically mounted in the bridge, you hear a much different sound than any magnetic type guitar as any magnetic type pickup has the typical "electric guitar sound". This is because at low listening levels the human ear is most sensitive between about 3 to 5 kHz where most electric guitar pickups have some resonant peak. Look up Fletcher-Munson Curve to see how the sensitive region of human hearing typically matches the resonant area of most guitar pickups. Granted, magnetic guitar pickups will never pickup any acoustic qualities but there is an "electric guitar" sound.

Magnetic pickups can be made to sound less electric or more acoustic by not putting the resonant point in the 3 to 5kHZ range by winding about one tenth the amount of turns (500 to 600 turns) and then use active electronics to boost the signal or carefully select a mic matching transformer mounted at the amp end of the cable to eliminate the cable capacitance effect or just target the input impedance of a mic mixer with an actual input impedance of 2400 ohms which properly loads a low impedance microphone rated at 150 ohms but with an actual range of about 100 to 250 ohms.

After market pickups evolved to target famous guitar player sounds with all types of marketing terms such as Eric Clapton "woman tone". Then, when we collectively like a certain type of sound, we turn to technology such as Zollner's work to attempt to decompose the pickup design to better understand all the variables involved.

Joseph J. Rogowski

[Antigua]

This information is contained in the coloured illustrations of page 5-31, German book version of PotEG.

Thanks, I'll take a look.

Sorry, this sentence is too complicated for me. But sounds like pure speculation without reasoning.

Wouldn't it make sense to ask for clarification before passing judgement?

Aperture corresponds to the magnetized string length. It is roughly given by twice the pole diameter of a SC (as measured by Zollner). Extension of primary flux close to string must be smaller than aperture. I have not seen any evidence of a frequency-dependance of the aperture up to now.

J Donald Tillman has authored a few web pages on the subject Response Effects of Guitar Pickup Position and Width and Guitar Pickup Response Demonstration . Even though it's based on theory and doesn't contain empirical evidence, the reasoning is sound: if the physical length of the harmonic oscillation is close to half that of the aperture width, then you will have two opposite phase instances of that harmonics within the aperture, causing a cancellation of that harmonic. For nearly all pickups on the market, the pole piece is small enough that the harmonic cancellations would effect very high frequencies.

[Antigua]

Short wide pickups like a P90 of Jazzmaster keep more wire closer to the string up to the point where adding more wire has a diminishing return not only in output level ...

I'm skeptical as to how much output is produced by the outer winds of a Jazzmaster pickup in particular, because it is especially flat, but very similar to a Stratocaster pickup otherwise, and yet I don't suspect that a Jazzmaster pickup is correspondingly louder than a Strat pickup, having both types of guitar and using them often. If we were to assume the outer winds were on par with the inner winds in terms of voltage, then a JM pickup should be loud, louder than a Filter'tron, nearly as loud as PAF.

I'm willing to put this to the test, though. I'll find one of each with similar electrical values and compare them.

... but in length of the string that is generating voltage with some upper harmonics being out of phase with very wide pickup designs.

Assuming we're talking about the Tillman comb filtering I linked above, it's a given the flux is most dense above the pole piece, and it that spreads outwards over the pickup, towards the string. At this point, the string is as magnetized as much as it can be, and making the coil wider doesn't change this area of magnetization. Therefore, the coil plays the role of observing that which has already been determined, and so it neither increases nor decreases Tillman-described harmonic cancellations.

I agree with you that the shape of the magnetic field differs with the more stubby AlNiCo pole piece, compared to the taller pole piece of a Strat/Tele/Jaguar pickup, due to the lower coercive force of AlNiCo causing it's field shape to be more subject to the geometry of the magnetic itself, but referencing Tillman again, the difference in aperture width, of say two or three millimeters, would be too trivial to make an audible difference.

[Helmholtz]

J Donald Tillman has authored a few web pages on the subject Response Effects of Guitar Pickup Position and Width and Guitar Pickup Response Demonstration . Even though it's based on theory and doesn't contain empirical evidence, the reasoning is sound: if the physical length of the harmonic oscillation is close to half that of the aperture width, then you will have two opposite phase instances of that harmonics within the aperture, causing a cancellation of that harmonic. For nearly all pickups on the market, the pole piece is small enough that the harmonic cancellations would effect very high frequencies.

Yes, this is the well known comb filter effect caused by a finite aperture. The calculation is based on a constant aperture. The author's statement that the aperture is given by the width of the PU is wrong. The shape of the coil doesn't influence the aperture. The measured aperture of a P-90 (10..13mm) is only marginally wider than that of a strat PU (8..10mm).

[Antigua]

Yes, this is the well known comb filter effect caused by a finite aperture. The calculation is based on a constant aperture. The author's statement that the aperture is given by the width of the PU is wrong. The measured aperture of a P-90 (10..13mm) is only marginally wider than that of a strat PU (8..10mm).

You had said "I have not seen any evidence of a frequency-dependance of the aperture up to now.", maybe this is a simple miscommunication, but I would describe comb filtering as a frequency dependence.

[Helmholtz]

You had said "I have not seen any evidence of a frequency-dependance of the aperture up to now.", maybe this is a simple miscommunication, but I would describe comb filtering as a frequency dependence.

It is not a frequency-dependance that is influenced by the shape of the coil. The returning flux has the same frequency-dependance as the primary flux.

[Mike Sulzer]

This information is contained in the coloured illustrations of page 5-31, German book version of PotEG.



Sorry, this sentence is too complicated for me. But sounds like pure speculation without reasoning. Aperture corresponds to the magnetized string length. It is roughly given by twice the pole diameter of a SC (as measured by Zollner). Extension of primary flux close to string must be smaller than aperture. I have not seen any evidence of a frequency-dependance of the aperture up to now.

There is another component to the aperture, more important for steel pole pieces than alnico. A high permeability pole piece increases the flux from the vibrating string most effectively when the source of the flux is right over it. You can see this by using a very small exciter coil and making measurements in various positions. This is not a big effect, but because of it, the aperture from the two effects is somewhat smaller than from the magnetization alone.