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Post by aquin43 on Jan 28, 2019 13:16:49 GMT -5
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. Are you really saying that C D E F is not a loop? Is that because the ends are taken back under the back plate?
C D E F with the magnet and back plate looks to me to have the geometry of Dearmond model 1000 but without the flanges.
C D and E F are in different parts of the electric field caused by the string modulation of the flux through the magnet and so there will be a voltage between C and F which will be communicated to the terminals at A and H via the wires under the back plate. Those will not be in the same electric field.
The loop doesn't have to be packaged neatly in a coil. Any separated wires will sense the electric field.
Arthur
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Post by ms on Jan 28, 2019 14:24:39 GMT -5
Of course CDEF is not a loop; it is part of one;. I agree that the cancelation is not complete, that is, unless the fold back is perfectly flat. And if it is not flat and the flux above and below the back plate is not the same, then flux is escaping out the sides. Then the output should be thought of as a result of flux pointed sideways through the two loops formed by the thickness of the fold back. You can do the integral as you wish, but if the coils have multiple turns, then this is a much easier way to look at it.
Antigua: yes the picture you posted is essentially the same as the pickups under discussion here. The coils extend down to the base plate which you can see.
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Post by aquin43 on Jan 28, 2019 17:01:01 GMT -5
Of course CDEF is not a loop; it is part of one;. I agree that the cancelation is not complete, that is, unless the fold back is perfectly flat. And if it is not flat and the flux above and below the back plate is not the same, then flux is escaping out the sides. Then the output should be thought of as a result of flux pointed sideways through the two loops formed by the thickness of the fold back. You can do the integral as you wish, but if the coils have multiple turns, then this is a much easier way to look at it. I see - you think that the voltages induced in A B and G H should cancel those in C D E F, but why should they? They are below the back (or centre) plate which is a low reluctance path shielding that region from the signal flux in the upper part of the pickup.
Another thing to ponder is that the overall construction and two main coils of the pickup as described, A B C D and E F G H, exhibit perfect anti-symmetry. There can, therefore, be no output from the sum of the direct excitations of these two coils which will always be exactly equal and opposite.
Arthur
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Post by ms on Jan 28, 2019 19:25:41 GMT -5
[quote timestamp="1548703479" Another thing to ponder is that the overall construction and two main coils of the pickup as described, A B C D and E F G H, exhibit perfect anti-symmetry. There can, therefore, be no output from the sum of the direct excitations of these two coils which will always be exactly equal and opposite. Arthur Field lines coming down from the string turn sideways and thus have components through the coils ABCD and EFGH. But these components point in the opposite directions, and therefore the signals reinforce when the coils are connected with opposite polarity.
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Post by antigua on Jan 29, 2019 1:33:09 GMT -5
I hope you consider doing that inductance test I mentioned, each coil by itself, and then both together. I think that would be valuable information about the nature of the side winder configuration. My guess would be that the two coils don't actually couple well enough to reduce the inductance by more than 100mH.
I might be able to something similar with a couple Strat pickups, but I'm not sure it would be perfectly representative. I would buy one for testing, but I have no desire at all to actually install such a pickup in a guitar. Much like stacked humbuckers, the only ones Ive tested are ones that I had ended up with by chance.
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Post by aquin43 on Jan 29, 2019 5:06:16 GMT -5
[quote timestamp="1548703479" Another thing to ponder is that the overall construction and two main coils of the pickup as described, A B C D and E F G H, exhibit perfect anti-symmetry. There can, therefore, be no output from the sum of the direct excitations of these two coils which will always be exactly equal and opposite. Arthur Field lines coming down from the string turn sideways and thus have components through the coils ABCD and EFGH. But these components point in the opposite directions, and therefore the signals reinforce when the coils are connected with opposite polarity. Yes, my mistake, the ANTI-symmetry is what allows the summing.
Perhaps an experiment would be useful. I thought that an exciter coil taped to a metal plate would act as a simple model of the magnetic circuit if we assume that the pickup is linear enough for reciprocity to apply . The whole arrangement is very asymmetrical in relation to the strings so one would expect the string signal to be small below the backplate, probably small enough to leave out of an initial model. The various loops and coils could be modelled with single turns so it would be possible to determine exactly where the induction occurs.
Arthur
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Post by ms on Jan 29, 2019 6:56:54 GMT -5
I hope you consider doing that inductance test I mentioned, each coil by itself, and then both together. I think that would be valuable information about the nature of the side winder configuration. My guess would be that the two coils don't actually couple well enough to reduce the inductance by more than 100mH. I might be able to something similar with a couple Strat pickups, but I'm not sure it would be perfectly representative. I would buy one for testing, but I have no desire at all to actually install such a pickup in a guitar. Much like stacked humbuckers, the only ones Ive tested are ones that I had ended up with by chance. These are expensive pickups, and taking them apart far enough to get at the individual coil wires is too risky for me. However, parts will be coming soon for my sidewinder project, and it will be easy to make those inductance tests both with a ferrite core running straIght through both coils and with separate cores with the coils coupled only by magnets. Most people do not understand sidewinders very well, and so it is a good idea to find out as much about them as possible.
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Post by aquin43 on Jan 29, 2019 17:08:57 GMT -5
I tried making a physical model and got some interesting results. I started a new thread.
Arthur
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Post by antigua on Feb 2, 2019 3:28:11 GMT -5
Just for the fun of it, I've put two Strat pickups with close inductance in series, the Tone Emporium TE-O3 Big City '69 neck and middle. They have AlNiCo 5 pole pieces. Together, and apart their inductance is 5.090H (Ls @ 100Hz).
At 1 inch distance, the inductance drops to 5.00H.
At 0.5 inch distance, the inductance drops to 4.95H.
At 0.25 inch distance, the inductance drops to 4.80H.
When the pickup stuck together, the inductance drops to 4.4H
So a 0.25 inches the inductance drops about 4%, but if the coupling really strong, it looks like the inductance could drop to the tune of 10%
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Post by ms on Feb 2, 2019 6:05:20 GMT -5
Just for the fun of it, I've put two Strat pickups with close inductance in series, the Tone Emporium TE-O3 Big City '69 neck and middle. They have AlNiCo 5 pole pieces. Together, and apart their inductance is 5.090H (Ls @ 100Hz). At 1 inch distance, the inductance drops to 5.00H. At 0.5 inch distance, the inductance drops to 4.95H. At 0.25 inch distance, the inductance drops to 4.80H. When the pickup stuck together, the inductance drops to 4.4H So a 0.25 inches the inductance drops about 4%, but if the coupling really strong, it looks like the inductance could drop to the tune of 10% Yes, that is about what I would expect. But we will how much the coupling is also a function of the core material. This is not so simple to predict when the cores are short rather than a tightly coupled magnetic circuit such as an audio transformer.
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Post by antigua on Feb 2, 2019 7:11:33 GMT -5
I'm curious what the load peak frequency is the side winder pickups, because I notice that the 3.5H and 4.5H inductance values are a lot lower than is typical for a P-90, which is about 7 henries. The 200pF capacitance might bring the peak down a little, but even with a test capacitive load, these side winders should end up being a bit brighter than a typical P-90, by as much as several hundred hertz. The average resonant peak for the P-90s ive tested, with an added 470pF load, measured in the low 2kHz range.
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