Lindy Fralin Hum-Canceling AlNiCo P90 Set

[ms]

These are sidewinders; in this post let's review what a sidewinder is for and how it works.  The only measurements in this post are to describe the relative hum canceling abilities in different directions.

The purpose of a sidewinder is to allow hum reduction, requiring at least two coils, while using only one row of pole pieces so that the string is sampled over a length about equal to a pole piece rather than at two regions spaced by about one inch as a standard humbucker does.  There are compromises, as we shall see.

First consider a pole piece in the usual position with respect to the string.  It magnetizes a small region of the string in a direction along the axis of the pole piece.  When the string vibrates a fluctuating magnetic field is created.  The pole piece has a relative permeability greater than one, and it amplifies the field, or concentrates the field lines.  Since magnetic field lines have no ends, the field lines must loop around and reenter the string or pole piece.  Thus if they start out down through the pole piece, then  they point sideways before they turn back up.  Thus you can position a coil along each side of the row of pole pieces in order to intercept this "sideways" magnetic flux.  The coils have high permeability cores in order to get as much flux (fields lines per unit area) to pass through as possible.

Filed lines that turn in opposite directions also point in opposite directions, and so the two coils have to have opposite polarity in order for the signals to reinforce, or add.  A hum magnetic field passing straight through both coils thus cancels.

Now let us try to understand why the sidewinder is not quite as good at reducing him as a regular humbucker.  Start with a single coil pickup and a magnetic field B pointing in some arbitrary direction.  We can represent this field by three mutually perpendicular components.  Let one point along the axes of the pole pieces, the second  into the side of the coil, and the last  into the end of the coil.  The coil is sensitive only to the component that is along the pole pieces, assuming the coil is carefully wound.  The other two components do not pass through the turns of the coil, and so it does not see them.  So in order to make a humbucker we need to be concerned only with the one component.  So it makes sense to put a second coil beside the first with opposite electrical polarity, using opposite magnetic polarity as well so that the net effect is for the to signals to add, but for the hum to cancel.  So a humbucker rejects hum from the side and end because each single coil has no sensitivity in those directions, and it rejects it in the direction of the axis of the pole pieces because a cancellation has been implemented.

Each coil of a sidewinder picks up from a field directed into the side of the pickup, but they cancel out when combined. The coils would also be expected to reject hum into their sides (that is, in the direction of the pole pieces) and their ends because that is what coils naturally do.  However, this is not quite right because of the high permeability steel.  That is, the pole pieces are somewhat magnetized by a hum B field along their axes, and there must be flux looping around and returning to them.  Thus there is a component of hum flux induced by a field along the pole pieces passing through the coils.  That is, in order to get signal we must also get some hum, but we expect the hum to be not so much because the incident hum field does not naturally curve as the signal does.  This would be hard to compute, and it is easier to measure the different levels of hum pickup in the different directions.

The test hum field is generated by what I call a "field bucket", a cylindrical plastic bucket with straight sides which once contained some kind construction material, or whatever, with turns of copper designed to produce straight field lines near the center of the bucket when excited with an ac current.  I have made casual measurements that illustrate the sensitivity in different directions, using the neck pickup of this set.  When the pickup is oriented in the bucket so that the field enters its end, we get a hum level which I call the reference, 0 db.  When the field enters the side of the pickup (along the axes of the coils), the  level is about 5 db higher.  When the field is along the pole pieces (that is entering the sides fo the coils), it is between 8 and 13 db higher than the reference, depending on the frequency, etc.

So this appears to justify the above description of how a sidewinder works.  I do not think it is very easy to understand them in perfect detail!

There is one other interesting effect.  When the field is oriented along the pole pieces (the worst case) it is possible to lower the hum pickup by placing a selected piece of ferrite near the side of the pickup.  This is difficult to get right, but it shows that the hum rejection might be further improved by careful design.

In a later post, time permitting, I will describe why I think P-90 sidewinders are interesting and useful, and then look at the impedances and frequency response of this AlNiCo set.

[antigua]

So if I understand correctly, the issue is that the two coils share a common axis, rather than having distinct axis? Aside from the fact that a stacked humbucker often uses lower permeable AlNiCo pole pieces, do you think the same drawbacks apply to stacked humbuckers?

I can't think of a better way to make a noise cancelling P-90 except to do what Mojotone did with Strat pickups, and that's to hide a dual rail humbucker under a cover that looks like a Strat single coil. You get the benefits of a side-by-side humbucker, with a nearly-as-narrow magnetic "window" as that of a single axis pickup. Those rail pickup require very fine wire in order to accomplish what they do, which I think that's another underutilized technique. Finer wire allows pickup makers to miniaturize the coils, and achieve a higher density of wire turns in the locations where they can produce the most signal, and least noise, which is essentially how a Lace Sensor relates to a traditional Strat pickup. 

[ms]

Jan 18, 2019 2:22:10 GMT -5 antigua said:

So if I understand correctly, the issue is that the two coils share a common axis, rather than having distinct axis? Aside from the fact that a stacked humbucker often uses lower permeable AlNiCo pole pieces, do you think the same drawbacks apply to stacked humbuckers?

I can't think of a better way to make a noise cancelling P-90 except to do what Mojotone did with Strat pickups, and that's to hide a dual rail humbucker under a cover that looks like a Strat single coil. You get the benefits of a side-by-side humbucker, with a nearly-as-narrow magnetic "window" as that of a single axis pickup. Those rail pickup require very fine wire in order to accomplish what they do, which I think that's another underutilized technique. Finer wire allows pickup makers to miniaturize the coils, and achieve a higher density of wire turns in the locations where they can produce the most signal, and least noise, which is essentially how a Lace Sensor relates to a traditional Strat pickup. 

The issue with the sidewinder is that the flux from the vibrating string is not along the axis of the coils.  The stacked humbucker is not a problem in this regard.  Its main problem is that the second coil does not add to the signal, and so output tends to be low.

I think the sidewinder offers interesting possibilities, and the size of the P-90 is better for experimentation because is bigger than a strat pickup, and parts are available.  Part of my motivation for buying these pickups was to learn about hum-canceling P-90s, and I will be using them in a project I am working on, possibly trying out similar pickups of my own design.  I would use ferrite instead of steel in the coils to see how high the Q of the resonance can be and then introduce damping in various ways to see how things change.

[ms]

Here are the impedance measurements of the neck and bridge pickups.  The capacitances are surprisingly high.  I wonder if this means that the coils are in parallel rather than series.  Although I ordered the pickups with four wires plus shield, they came with just a single conductor shielded cable, and it would not be easy to find out how they are wired.

The eddy current losses are greater than expected for alnico, but less than many humbuckers.  It would appear that this is the result of using a thin steel blade in the coils. (It looks like steel.)  Now, what makes a strat pickup a strat pickup is the alnico in the coil, not the alnico itself.  The alnico pole ;pieces do not do the same thing here since they are not in the coil.  It is true that there is less steel here than in a standard P-90, but this is to quire what I expected.


You could make an Alnico sidewinder in a P-90 size by using minihumbucker coils, putting the Alnico bar magnets in both, like a Firebird pickup.  Then you could turn the coils sideways, make a structure to go between and mount the assembly on a P-90 base plate.  You could use P-90 screws for poles, which would have less effect than normal since they are not in the coils, or you could use some other kind of pole pieces.  This might no work so well because of the low permeability of Alnico.  I would prefer to use ferrite in the coils, and achieve the right level of damping by various possible means.

[antigua]

I think they're wired in series based on the L and R values, I think the C might be high due to coupling between the coil and the steel blade core. I usually measure high C values for "blade" single coil sized humbuckers wired in series.


I was pondering whether it would be better to leave the steel blade cores ungrounded, but straylight made the case that this could increase the noise, especially when you touched them with your fingers. Maybe a ferrite core could solve the problem. 

[ms]

Jan 21, 2019 5:35:36 GMT -5 antigua said:

I think they're wired in series based on the L and R values, I think the C might be high due to coupling between the coil and the steel blade core. I usually measure high C values for "blade" single coil sized humbuckers wired in series.


I was pondering whether it would be better to leave the steel blade cores ungrounded, but straylight made the case that this could increase the noise, especially when you touched them with your fingers. Maybe a ferrite core could solve the problem. 

Thanks for the reply.  I will verify later that the blades are grounded, and that would settle it.  Yes, this is another reason to use ferrite for blades.  But it has to be tried; sometimes you get surprised!

[ms]

I measured the neck pickup.  The pole pieces and blades are connected to the baseplate through the screws that hold the baseplate on.  The base plate is grounded through the lug on the cable shield. I made the measurements above with the lug removed from the base plate (to avoid the secondary resonance).  Thus the blades were not grounded, and we need another explanation for the high capacitance. 

[antigua]

Jan 21, 2019 16:25:21 GMT -5 ms said:

I measured the neck pickup.  The pole pieces and blades are connected to the baseplate through the screws that hold the baseplate on.  The base plate is grounded through the lug on the cable shield. I made the measurements above with the lug removed from the base plate (to avoid the secondary resonance).  Thus the blades were not grounded, and we need another explanation for the high capacitance. 

The other aspect is coil geometry. It appears to me, based on the high capacitance of Tele neck pickups (~225pF), and the low capacitance of flat Jazzmaster pickups (~40pF), that the further apart the the start layer and end layers of the coil, the lower the capacitance will be, since this puts more overall spatial separation across the sides of the circuit. With a Tele neck pickup, this distance is tiny, maybe two to three millimeters, but on a Jazzmaster pickup, this distance is great, closer to 12 millimeters (I'm measuring with my mind's eye). Since a P-90 is very flat, I'm guessing these horizontally oriented coils are very tall and thin, when stood up, which puts a small distance between coil start and coil end. 

In another forum, there was talk about partitioning a tall and thin coil into a lot of small, flat coils, all stacked on top of each other. Imagine a roll of Life Savers, where each Live Saver is a coil, connected to the next in series. This way, the total spatial separation between start and end of the coil does not extend across it's entire length and width, but only in a diagonal direction, following along with the coil partitions, like a step ladder. The sum total of separation would be a lot greater, and so the capacitance should be a lot lower. 

[ms]

Jan 21, 2019 16:42:21 GMT -5 antigua said:

The other aspect is coil geometry. It appears to me, based on the high capacitance of Tele neck pickups (~225pF), and the low capacitance of flat Jazzmaster pickups (~40pF), that the further apart the the start layer and end layers of the coil, the lower the capacitance will be, since this puts more overall spatial separation across the sides of the circuit. With a Tele neck pickup, this distance is tiny, maybe two to three millimeters, but on a Jazzmaster pickup, this distance is great, closer to 12 millimeters (I'm measuring with my mind's eye). Since a P-90 is very flat, I'm guessing these horizontally oriented coils are very tall and thin, when stood up, which puts a small distance between coil start and coil end. 

In another forum, there was talk about partitioning a tall and thin coil into a lot of small, flat coils, all stacked on top of each other. Imagine a roll of Life Savers, where each Live Saver is a coil, connected to the next in series. This way, the total spatial separation between start and end of the coil does not extend across it's entire length and width, but only in a diagonal direction, following along with the coil partitions, like a step ladder. The sum total of separation would be a lot greater, and so the capacitance should be a lot lower. 

The coils in these pickups have an almost square cross section, looking into the end.  When you put coils in series, the capacitance of the combination is lower than an individual coil, and so I do not think it should be so high. 

[stratotarts]

It might have been overwound "hot" to compensate for the inherent losses of a sidewinder. That would boost the capacitance, I think. Keep in mind, the inductance of the two series coils is reduced substantially by the mutual coupling of the two coils, since they are collinear and opposite in phase.  This effect was confirmed by my experiments with home brew sidewinders, although I can't report much detail because it was some time ago. The overall device inductance affects what you think the capacitance "should be".

[ms]

Jan 22, 2019 11:57:57 GMT -5 stratotarts said:

It might have been overwound "hot" to compensate for the inherent losses of a sidewinder. That would boost the capacitance, I think. Keep in mind, the inductance of the two series coils is reduced substantially by the mutual coupling of the two coils, since they are collinear and opposite in phase.  This effect was confirmed by my experiments with home brew sidewinders, although I can't report much detail because it was some time ago. The overall device inductance affects what you think the capacitance "should be".

Interesting about the mutual coupling. I have not been thinking about that, a mistake, but I will.  But first, I am wondering about the inherent losses of sidewinders; what are they?

I am thinking, at least at the moment,  that the negative mutual coupling is a good thing because it lowers the inductance (and thus raises the resonant frequency as resulting from external capacitance) without affecting the output level (at frequencies well bellow the resonance).

[stratotarts]

Jan 22, 2019 13:18:08 GMT -5 ms said:

Jan 22, 2019 11:57:57 GMT -5 stratotarts said:

It might have been overwound "hot" to compensate for the inherent losses of a sidewinder. That would boost the capacitance, I think. Keep in mind, the inductance of the two series coils is reduced substantially by the mutual coupling of the two coils, since they are collinear and opposite in phase.  This effect was confirmed by my experiments with home brew sidewinders, although I can't report much detail because it was some time ago. The overall device inductance affects what you think the capacitance "should be".

Interesting about the mutual coupling. I have not been thinking about that, a mistake, but I will.  But first, I am wondering about the inherent losses of sidewinders; what are they?

I am thinking, at least at the moment,  that the negative mutual coupling is a good thing because it lowers the inductance (and thus raises the resonant frequency as resulting from external capacitance) without affecting the output level (at frequencies well bellow the resonance).

Well, I have an opinion about the losses, but since the emphasis here is on demonstrable facts, I'll hold on to most of it for now, because I have to admit that I have not been able to verify it yet. But I think it's because the string field density is lower on the lower half of each coil (furthest away from the string). I had a long email discussion with Tucson about the general idea of measuring coil sensitivity (rather than about sidewinders), and he steered me towards a view that only considers the total flux density inside the coil loop, discounting the validity of considering parts of the loop separately. However, I think everyone could still accept that the off axis flux density of the string field is less than the on axis density. In other words, I think both "views" produce the same results in practice. Check it out and then use whatever explanation makes you happy, is my attitude. I haven't had time lately for in depth research.

Yes, the reduction in inductance is a surprise bonus, increasing the frequency response with apparently no penalties. Another interesting question is, whether poles are really necessary inside the coils. The prototypes I built didn't have any. So little time.

[ms]

Jan 22, 2019 13:52:52 GMT -5 stratotarts said:

Jan 22, 2019 13:18:08 GMT -5 ms said:

Interesting about the mutual coupling. I have not been thinking about that, a mistake, but I will.  But first, I am wondering about the inherent losses of sidewinders; what are they?

I am thinking, at least at the moment,  that the negative mutual coupling is a good thing because it lowers the inductance (and thus raises the resonant frequency as resulting from external capacitance) without affecting the output level (at frequencies well bellow the resonance).

Well, I have an opinion about the losses, but since the emphasis here is on demonstrable facts, I'll hold on to most of it for now, because I have to admit that I have not been able to verify it yet. But I think it's because the string field density is lower on the lower half of each coil (furthest away from the string). I had a long email discussion with Tucson about the general idea of measuring coil sensitivity (rather than about sidewinders), and he steered me towards a view that only considers the total flux density inside the coil loop, discounting the validity of considering parts of the loop separately. However, I think everyone could still accept that the off axis flux density of the string field is less than the on axis density. In other words, I think both "views" produce the same results in practice. Check it out and then use whatever explanation makes you happy, is my attitude. I haven't had time lately for in depth research.

Yes, the reduction in inductance is a surprise bonus, increasing the frequency response with apparently no penalties. Another interesting question is, whether poles are really necessary inside the coils. The prototypes I built didn't have any. So little time.

The high permeability material inside the coil should cause a few times higher flux to pass through as many turns of the coil as it can, thus increasing the output.  Not necessary, but probably necessary to make the sidewinder "competitive" in that sense.

So I am thinking that a side winder in a P-90 format should look like this:

Ferrite in the coils, continuous from one coil through the next to encourage as much mutual coupling as possible.
Ferrite string pole pieces that sit flat on that piece of ferrite.  That is, nothing goes  below that piece, and so as few field lines as possible go around the coil rather than inside as many turns as possible.

I would like to have hollow ferrite pole pieces containing a screw just long enough to make them adjustable, but this requires some kind of threading inside, maybe not so easy.

I would use neo magnets between the pole pieces and just outside the nos. 1 and 6 strings.

[ms]

Here is a plot of the response of the neck pickup with an exciter coil.  The prediction of amplitude from the impedance measurement is plotted on top.  They are very close.  This means two things:
1.  This pickup has very little eddy current loss in addition to that measured with the impedance.
2.  I am getting better at tracking down all the sources of C that need to be included in the calculation of response from the impedance.

The discrepancy above 10KHz might be due to such eddy currents losses, or to inaccuracies in the impedance measurement so far above resonance.

[ms]

I have been doing some work on displaying the results of the impedance measurements, in particular, using amplitude and phase rather than real and imaginary.  IMO, but this just does not do it.  My conclusion is that you need two plots or real and imaginary, one covering the full range of frequency and impedance to give an overall view of the pickup, and a second one up to 5 KHz only, displaying the more restricted Z values in this limited range to show accurately the effects at guitar frequencies.  In the second plot, only the impedance without the effect of the C is shown, along with the limiting gray lines.  For example, in the two attachments showing the impedance of the neck pickup under discussion here, you can see from the second plot that the dominant effect of the eddy currents is to raise the losses at 5KHz over an eddy current free pickup because the real part of Z at that frequency is about 4 to 5 times as large as the coil resistance.

[ms]

Just for comparison, here are the same two impedance plots for an AlNiCo single coil, no steel nearly.  The loss is measurable, but much less.

[aquin43]

Jan 22, 2019 14:55:10 GMT -5 ms said:

So I am thinking that a side winder in a P-90 format should look like this:

Ferrite in the coils, continuous from one coil through the next to encourage as much mutual coupling as possible.
Ferrite string pole pieces that sit flat on that piece of ferrite. That is, nothing goes below that piece, and so as few field lines as possible go around the coil rather than inside as many turns as possible.

I would like to have hollow ferrite pole pieces containing a screw just long enough to make them adjustable, but this requires some kind of threading inside, maybe not so easy.

I would use neo magnets between the pole pieces and just outside the nos. 1 and 6 strings.

Doesn't the mutual coupling reduce the output? Mutual coupling implies shared flux and any modulation of flux shared by the coils cancels out so that if they were perfectly coupled there would be no inductance but also no leakage flux so no output.

It seems to me that the sidewinder can be reduced to two U shaped pickups side by side. They are opposite ways around so that the coils can be wired in opposition to cancel external hum. There would be comb filtering because of the pole pairs, so the outer set of poles in each pickup is cut back to make their coupling with the string diffuse. This raises the impedance of the magnetic circuit, reducing the sensitivity.

Arthur

[ms]

Jan 27, 2019 9:58:32 GMT -5 aquin43 said:

Jan 22, 2019 14:55:10 GMT -5 ms said:

So I am thinking that a side winder in a P-90 format should look like this:

Ferrite in the coils, continuous from one coil through the next to encourage as much mutual coupling as possible.
Ferrite string pole pieces that sit flat on that piece of ferrite. That is, nothing goes below that piece, and so as few field lines as possible go around the coil rather than inside as many turns as possible.

I would like to have hollow ferrite pole pieces containing a screw just long enough to make them adjustable, but this requires some kind of threading inside, maybe not so easy.

I would use neo magnets between the pole pieces and just outside the nos. 1 and 6 strings.

Doesn't the mutual coupling reduce the output? Mutual coupling implies shared flux and any modulation of flux shared by the coils cancels out so that if they were perfectly coupled there would be no inductance but also no leakage flux so no output.

It seems to me that the sidewinder can be reduced to two U shaped pickups side by side. They are opposite ways around so that the coils can be wired in opposition to cancel external hum. There would be comb filtering because of the pole pairs, so the outer set of poles in each pickup is cut back to make their coupling with the string diffuse. This raises the impedance of the magnetic circuit, reducing the sensitivity.

Arthur

Inductance (mutual or otherwise)  is the result of current flowing in some turn of a coil inducing voltages around each of the other turns (same or other coil).  First consider low frequencies.  The load on the pickup (capacitive and resistive) is very high and thus very little current flows.  That is, the inductive reactance of the coil is small.  Thus even if the mutual coupling were to cause canceling at higher frequencies, there can be no cancellation at low frequencies. The voltage induced through the two coils by the changing flux from the string simply add in phase.

But this adding in phase is true at any frequency, but at higher frequencies we have more current flowing. Inductance matters, and then the out of phase coils result in the cancelation of induced voltages, but only the induced voltages due to current flow, not due to the flux from the string.  Thus the inductance is reduced, but that is all that happens.

[aquin43]

Regardless of frequency, if the coils have a coupling coefficient of k, doesn't that mean that a fraction k of the total flux in the coils is shared? That shared flux, if modulated by the string, can produce no output because the coils are wired in opposition.

Arthur

[ms]

Jan 27, 2019 13:43:34 GMT -5 aquin43 said:

Regardless of frequency, if the coils have a coupling coefficient of k, doesn't that mean that a fraction k of the total flux in the coils is shared? That shared flux, if modulated by the string, can produce no output because the coils are wired in opposition.

Arthur

The concept of shared flux is a result of k12 = k21.  From which ever side you look at it, current in one makes a magnetic field the induces a voltage in the other.  But that is independent of the flux from the string, which points in opposite directions through the two coils and thus induced voltages add.

We have two sides to a pickup:
1. The induced voltage, determined by the law of magnetic induction.
2.The voltage that you can access, which is a function of the circuit operating on the induced voltage.

.

[antigua]

I can't confirm or deny the theory behind this, but I took a generic humbucker model and modeled what happens if you just increase the inductive coupling of the two inductors, and interestingly enough, it just shows the peak frequency increasing, which corresponds with the inductance dropping, and no attenuations otherwise.

[aquin43]

What is the geometry of these pickups? Are they the same as in the Lawrence patent

patentimages.storage.googleapis.com/45/5d/fa/ea74ddf1d28c5a/US3902394.pdf

The patent states that "... for reasons not known, this particular pickup construction works fantastically well."

It seems to me that the pickup can be reduced to two opposite polarity single coil pickups stacked back to back vertically. The top pickup that faces the strings has a coil that consists of two half coil bundles with the circuit completed via the other half coils. The string excitation will induce a voltage in each wire of each of these bundles and because there is an overall complete circuit these voltages will add just as they would in an ordinary coil.

Two single coils back to back would achieve the same output but their coils would be shielded from each other instead of being coupled via the shared magnetic divider as here.

Arthur

[ms]

Jan 28, 2019 4:35:12 GMT -5 aquin43 said:

What is the geometry of these pickups? Are they the same as in the Lawrence patent

patentimages.storage.googleapis.com/45/5d/fa/ea74ddf1d28c5a/US3902394.pdf

The patent states that "... for reasons not known, this particular pickup construction works fantastically well."

It seems to me that the pickup can be reduced to two opposite polarity single coil pickups stacked back to back vertically. The top pickup that faces the strings has a coil that consists of two half coil bundles with the circuit completed via the other half coils. The string excitation will induce a voltage in each wire of each of these bundles and because there is an overall complete circuit these voltages will add just as they would in an ordinary coil.

Two single coils back to back would achieve the same output but their coils would be shielded from each other instead of being coupled via the shared magnetic divider as here.

Arthur

I cannot tell which way the cols are wound in that diagram. Here we are discussing sidewinders, with the coils turned 90 degrees from the usual way.

[aquin43]

It is rather unclear for a patent isn't it? It is  a sidewinder; the coils are on their sides, but you have to look very closely at the diagram to see it. The coil former cross sections at 16 and 17 tell the tale.

The initial reference was

www.billlawrence.com/Pages/Steel_Guitar/900info.htm

which has a small picture:

Arthur

[ms]

Jan 28, 2019 6:16:05 GMT -5 aquin43 said:

It is rather unclear for a patent isn't it? It is  a sidewinder; the coils are on their sides, but you have to look very closely at the diagram to see it. The coil former cross sections at 16 and 17 tell the tale.

The initial reference was

www.billlawrence.com/Pages/Steel_Guitar/900info.htm

which has a small picture:

Arthur

Patent standards are ridiculously low but this : "... for reasons not known, this particular pickup construction works fantastically well." is idiotic. It says:  "This invention fell out a tree and hit me in the head, and therefore I am patenting it."

The mud bucker has been around since the 60s, I believe.  I think patents from then are not in force any more, and I also suspect that the people making the mud bucker did not understand what they were doing, but that is normal in the pickup business.

[aquin43]

The sidewinder simplified. I tried to visualise how the sidewinder actually works and came up with the following simplified diagram which is intended to be a top view of the pickup with the coils reduced to single turns:

The two main coils are A B C D and E F G H which are connected in anti-phase and the sensing loop is C D E F, the ends of which are brought out under the back plate at A and H.

Thus the two coils are not directly involved in the sensing. It is the voltages induced in their halves above the backplate, C D and E F, that produce the output.

The voltages induced in the two loops  A B C D and E F G H by externally applied fields cancel. So do the  voltages in the loops C D E F and A B F H if the whole system is made symmetrically as in the patent.

The two loops A B C D and E F G H are in series with the output and are also mutually coupled via the back plate. This coupling reduces their combined inductance.

The two loops C D E F and A B F H are also in series with the output. They are coupled to some extent by the path through the magnet and the back plate.

In the perfectly symmetrical pickup, the back plate carries no static flux, only the signal.

Arthur

[antigua]

I think pictures of the pickup in question would be worth a thousand words in this case. 

I found a pick of his noiseless Jazzmaster pickups with the cover removed, is this pretty much the same thing?





I think an interesting experiment would be to take a regular P-90, and use an exciter coil to produce bode plots of the Fralin sidewinder, and the P-90, to see how much different the output voltage is for a constant input. I can see why the output would be similar, it appears that the side-laying coils occupy most of the same space that a single upright coil would occupy. 

As for the inductance, maybe it's possible to disconnect the coils and get inductance readings from to coils separately with an LCR meter, and then assume the ideal inductance would be the two coils summed, and then see how close that value comes to 3.6H, we're assuming the sum would be a little higher. 

[ms]

Jan 28, 2019 9:54:18 GMT -5 aquin43 said:

The sidewinder simplified. I tried to visualise how the sidewinder actually works and came up with the following simplified diagram which is intended to be a top view of the pickup with the coils reduced to single turns:

The two main coils are A B C D and E F G H which are connected in anti-phase and the sensing loop is C D E F, the ends of which are brought out under the back plate at A and H.

Thus the two coils are not directly involved in the sensing. It is the voltages induced in their halves above the backplate, C D and E F, that produce the output.

The voltages induced in the two loops  A B C D and E F G H by externally applied fields cancel. So do the  voltages in the loops C D E F and A B F H if the whole system is made symmetrically as in the patent.

The two loops A B C D and E F G H are in series with the output and are also mutually coupled via the back plate. This coupling reduces their combined inductance.

The two loops C D E F and A B F H are also in series with the output. They are coupled to some extent by the path through the magnet and the back plate.

In the perfectly symmetrical pickup, the back plate carries no static flux, only the signal.

Arthur

The sensing path that you describe is not a loop, and therefore there is nothing for voltage to develop around.  I think the relative hum measurements that I described in the first post verify that the sidewinder works as I described.

[ms]

Jan 28, 2019 12:04:02 GMT -5 antigua said:

I think pictures of the pickup in question would be worth a thousand words in this case. 

There are hundreds of pictures of side winders on the web. I thought they were sufficient to describe the operation, but I can post a picture if you like.  It is easy to remove some of the tape to get a better view of the blades, coil orientation, etc.

[antigua]

Jan 28, 2019 12:20:45 GMT -5 ms said:

Jan 28, 2019 12:04:02 GMT -5 antigua said:

I think pictures of the pickup in question would be worth a thousand words in this case. 

There are hundreds of pictures of side winders on the web. I thought they were sufficient to describe the operation, but I can post a picture if you like.  It is easy to remove some of the tape to get a better view of the blades, coil orientation, etc.

There's quite a few variations on sidewinder design, with different coil shapes, steel guides, magnet placement, etc. I edited my post above to include a pic of a Fralin JM sidewinder, maybe it's similar to that. I can't tell how deep the coils are from that pic though, also the coil cores are obscured, and whatever might be going on underneath.