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Post by ms on Jul 27, 2021 7:34:22 GMT -5
I think we are primarily concerned with hum (lower harmonics of 60 Hz, and buzz (somewhat higher harmonics). AK's test show difference mostly in the high frequencies. At high frequencies, metal shields can affect interference from magnetic sources as well as electric since the law of magnetic induction depends on the rate of change of flux. But that is not what the shielding needs to stop; rather it is the lower and medium frequencies where a metal shield is only effective against electric fields, what AK calls capacitive. I think the results of his tests are are not as useful as one would like. For example, for electric shielding, the material, as long as reasonably conductive, should not make much difference. Also, if he is measuring the effect of electric fields, there should be a big difference between shield and no shield at the lower frequencies. There is not. Therefore, I think he is seeing mostly magnetic interference , and at high frequencies. This is not so helpful because we know that the magnetic interference that is most a problem is lower frequencies, and that requires cancelation with two coils.
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Post by ms on Jul 24, 2021 6:42:40 GMT -5
If you introduce hum differences between the middle on the one hand and the neck and bridge on the other, you should suspect that the pickups are wired with the middle out of phase in order to cancel (magnetic) hum when the middle and one of the others are used at once.
The larger question is why are you doing this? In most situations, the dominant hum with SC pickups is magnetic, not electric, and shielding can only get rid of electric, while cancellation (two coils) reduces magnetic.
If putting in a shield makes a big difference, I would suspect that maybe something is wrong with how the guitar is wired. But who knows? It is hard to tell remotely.
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Post by ms on Jul 14, 2021 10:00:42 GMT -5
The holes in the screen are small enough to reflect rf up to many, many GH; not an issue. I think the dominant eddy currents are around the sides of the cover, assuming a screen material of non-magnetic stainless.
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Post by ms on Jul 12, 2021 9:14:08 GMT -5
Should shield OK; what is the screen made of? The conductivity would affect the level of eddy currents.
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Post by ms on May 31, 2021 16:38:55 GMT -5
We have E = CV^2, and C = Q/V, and so E = QV. It seems to me that you want to wind the pickup so that the voltage goes down, not up (for a given current through the pickup). Then if you increase the current so that the voltage is the same as before, the charge increases and so the capacitance has increased, and the stored energy has gone up as it should . Consider it this way. The pickup is a generator with the generated voltage increasing from turn 1 to turn N because of an alternating magnetic field. At any time, energy will be stored in the capacitances between the windings in the amount 0.5CV^2, where C is the capacitance between a pair of physically adjacent turns and V is the voltage between physically adjacent turns. C is maximised if the turns lie parallel to one another and V is maximised if the physically adjacent turns are as far apart as possible in the winding sequence. The voltage increases from turn to turn depending only on the turn's status in the winding sequence, not on its position within the coil. This remains true even at low frequencies where the total capacitive current is insufficient to modify the voltage distribution within the coil. The problem can, in the first instance, be treated as a quasi-static one.
The previous analysis showed how the overall stored energy and hence effective capacitance could be reduced by adopting a particular layout. I am speculating that there are other layouts that can increase the effective capacitance by routinely bringing turns that are far apart in the winding sequence nearer to one another.
I agree that the method works, but suspect somewhat limited accuracy. The capacitances modify the voltages, and you cannot say that they all get modified by the same fractional amount. Thus the actual relative voltages are different from what the model assumes.
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Post by ms on May 31, 2021 6:25:09 GMT -5
Mr. Lemme: Your writing was the first intelligent material on pickups I found on the web some years ago. By the way, the web site is not accessible, but the pdf file is.
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Post by ms on May 31, 2021 6:18:39 GMT -5
I'm sure that 1. there's a lot more to a pickup's sound than just it's frequency response (but I'm somewhat ignorant of what that would be), and 2. There's more to an electric instrument's sound than just it's pickup. Although I will say that I've heard videos on Youtube of electric guitars built from glass, stone, concrete, styro-foam, and salt, and they still sound like electric guitars! Sure, there are differences, but compared to the difference made by pickup choice, guitar preamp circuit, amp speakers, and twists of bass/mid/treble knobs, the body material was insignificant (IMO). About equal to one notch on the treble knob on the amp. Most important: sampling a particular region of the string creates a certain pattern of harmonics that is a function of the active length of the string. As a wise person said many years ago: Put a strat pickup on an an acoustic guitar, and the resulting electric sound is nothing like a strat. Also, the magnitude of a difference might be small, but it nonetheless might be very significant because it is a very different kind of difference than you can achieve it by turning a knob or changing a resonant frequency.
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Post by ms on May 29, 2021 12:19:15 GMT -5
We had a thread recently discussing a winding method that reduced capacitance, in which Yogi B gave an analysis that related the distributed capacitance to the stored energy for a given applied voltage. This stored energy is related to the square of the mean inter-turn voltage.
The Suhr pickup has a capacitance that is roughly 1.75 that of a simple standard winding. If the trick is layering to increase the mean inter-turn voltage then it would only need to be increased by the square root of this or 1.32 times. It requires placing turns that are several winds apart near to each other.
We have E = CV^2, and C = Q/V, and so E = QV. It seems to me that you want to wind the pickup so that the voltage goes down, not up (for a given current through the pickup). Then if you increase the current so that the voltage is the same as before, the charge increases and so the capacitance has increased, and the stored energy has gone up as it should .
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Post by ms on May 29, 2021 10:22:16 GMT -5
My impression of "modern" stagger is that the pole under the G string is lower than implied by the fret board curvature because the plain (not wound) G string used in place of the wrapped one from the past has a larger mass of magnetic material. I think it is the copper that provides the strength to resist stretching, but when it does stretch (as it must with higher tensions), the insulation must stretch with it. Would a wound G in the same gauge set as with a plain G not be slightly thicker (with a thinner core for flexibility) to make up for the mass loss? I think the G pole is generally the same height as the D in a modern stagger, but there likely isn't a consensus on that among pickup makers. I imagine the vintage stagger was not only for the wound G, but to compensate for the relative output loss of the pure Ni wraps (Ni being only paramagnetic). Ni-plated Steel wraps better equalize string output. When I switched from Sfazrzo Nickeanium (Ni wraps) to the same gauge of V-strings (Ni/Fe wraps) on my guitar with flat-pole pickups, there was a marked increase in wound string output, at least for the lower harmonics, requiring a slight lowering of the low E side height. I think Greg Sfarzo had told me they are not wound as tight as the Nickelaniums, so they have weaker higher harmonics. Consider that the insulation facing outward would stretch around the bobbin ends more than the wire. Some wire deformity may also occur, but the outward-facing insulation would have the most stress and excess pressure on the still malleable stretched portions from consecutive layers also exceeding tension limits. It's nothing short of a full-on capacitive feeding frenzy! Stagger is kind of a subjective thing, and different people hear it differently. I like Kinman's solution (https://kinman.com/magnet_stagger.php), although I could argue all day with him about other things! Well, the outward facing insulation on the ends stretches more, but on the other hand the inward facing insulation stretches less. So I do not know what the net effect is, but perhaps not so much.
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Post by ms on May 29, 2021 5:51:45 GMT -5
Hi antiguaThanks for sharing this data. Few questions... #1 What do you mean by "modern" stagger. What's the main difference wrt vintage stagger? Do you know the polepiece height sizes? #2 Since the winding distribution is even, do you think that this is machine wound? #3 " If it's wire of the bridge pickup became thinner during the winding process due to high winding tension," -What do you mean by becoming thinner during the winding process? Do this happen with high winding tension? I tried winding with a higher tension than my normal (by hand) but I get an increase in capacitance. Thanks! #1) Modern stagger means it essentially follows the radius of an average fretboard for better balance with a plain G-string and steel wraps. #2) They are probably machine wound. Modern auto-winders can be programmed for different patterns and can control tension better than any human hand. #3) He may have meant that the insulation stretched. It's a common issue with poly wire. My impression of "modern" stagger is that the pole under the G string is lower than implied by the fret board curvature because the plain (not wound) G string used in place of the wrapped one from the past has a larger mass of magnetic material. I think it is the copper that provides the strength to resist stretching, but when it does stretch (as it must with higher tensions), the insulation must stretch with it.
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Post by ms on May 28, 2021 7:33:06 GMT -5
Did you try your pickup into an instrument input? I think it has enough output so that it would work.
The output impedance of a pickup is a complicated function of frequency, and the load it looks into with a normal guitar amp input is much higher at most frequencies. The amp input resistance can cause a little damping near the resonance, and its capacitance could lower the resonant frequency a bit, but neither is a huge effect. In your case, the load of the amp would do almost nothing, and so your very high frequency resonance might need a bit of damping, depending on the materials used in the pickup. If you use a volume control on this guitar, 25K would be a low enough value so that the tone would not be affected by its setting; that is, cable capacitance would have a very small effect. Also 25K would be high enough so that it would not affect the pickup much, except to damp the (ultrasonic) resonance, if it is significant.
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Post by ms on May 24, 2021 6:46:14 GMT -5
Reviving this old thread with some info that may be useful. I'm thinking that part of the reason different AlNiCo grades produce a different note timbre with the same coil is that permeability differences cause the lines to vibrate through the coil differently depending on how much the lines are pulled toward the core i.e more magnetic flux toward the middle of the coil with AlNiCo II or III vs V. The angle of the lines moving through the coil may also cause some cancelations depending on pickup height? This recent blog entry by Scott Lawing may shed some light on the subject, and is worth the read none the less. I really like how he explains things simply and with a touch of good humor: lawingmusicalproducts.com/dr-lawings-blog/the-wide-range-humbucker-and-the-genius-of-seth-lover Yes, I think that Scot is performing a real public service with his explanations, especially the idea that it is the magnetization of the string, induced by the pickup permanent magnet, that counts. The implication is that the field of the permanent magnet matters only where the string is. For some reason this idea upsets a lot people. I like his quotes from Seth Lover that show that Seth understood these ideas, providing support from one of the "pickup gods". I think the most important effect of different permeability material is to change how much voltage the current in one loop of wire induces in the other loops. That is, it is altering the inductance, changing the resonant frequency, and thus the "filter function" applied to the signal from the string.
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Post by ms on May 18, 2021 18:21:33 GMT -5
So I did a non-linearity test with a pickup in the strat neck position, fretted on the 12th. The pickup is a strat pickup sized sidewinder with high permeability poles. I measured the relative level of the 2nd harmonic and fundamental for two kinds of rapid picking: 1. very soft, and 2. very hard. In case 1, the result was about -21 db, and in case 2 about -11 db.
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Post by ms on May 9, 2021 12:51:10 GMT -5
If you accept Zollner's empirical formula for the effective signal flux in the coil as a function of distance from the pole in the strat pickup, which is effectively
flux ~ 1/(4.3 + d + x(t))
where d is the static string clearance and x the movement in mm, the distortion is as high as 16% for a 1mm peak string movement at Fender's preferred setting of 2mm for d.
It is the lack of intermodulation with the other strings that makes that sound OK. It probably adds to the fullness of the sound.
It changes the ratio of harmonics as a function time. Given that the ratio of harmonics is a function of time with no distortion, all it does is change the sound of the string a bit as a function of time. (Until you include the effect of the beating of natural and generated harmonics, probably a small effect, but nonetheless, something new.) I will have to check his derivation.
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Post by ms on May 9, 2021 10:35:51 GMT -5
I don't really understand how there would be significant wave asymmetry if there isn't significant flux change in the string, but that's on me. As for how a shorter denser coil would affect it, there are already stronger flux lines through more of the coil at a given distance, so why would there be more asymmetry rather than just more emphasized stronger string vibrations as I had originally thought? I fall in the: only the magnetized string matters camp, so I defer to the research of Dr. Scott Lawing. I'd be curious what he'd say about asymmetry: lawingmusicalproducts.com/dr-lawings-blog/how-does-a-pickup-really-workDo you wonder why the wave form's positive and negative sides of the cycle aren't the same? I think that's a case where the reluctance model makes it clear, in that when the string is moving closer, the reluctance (air gap) is decreasing, and when it's moving away, the reluctance is increasing. When the string is nearest to the coil, more lines of flux are involved with the coil, versus when it's further away. The peaks and troughs of the output waveform are of when the string velocity is at it's highest, which which is when it's physically passing the center point, and when the wave form is crossing the 0 and 180 degrees, that's when the string is physically either at the nearest point, or farthest point, from the the pickup. So the two sides of the wave form are, the string rushing away from the pickup, reluctance climbing, and then the string rushing towards the pickup, reluctance dropping. I think that the law of magnetic induction does a better job since you can count the number of flux lines passing through a loop of wire as a function of where the string is when given the form of the magnetic field. It appears to me that your discussion in the second paragraph shows that the distortion is not very big. The positive and negative peak voltages both occur in the same place in the magnetic field, but with oppositely directed motion. So the peak voltages have the same magnitudes. When the string is at either extremum the velocity magnitude is zero, and so the output voltages are zero, tending to hide the effects of different field strengths. That is, the zero crossings occur in the same placrs. I expect only a slight difference in the shape of the positive and negative half cycles from a sine wave motion. Maybe the asymmetrical appearance of the guitar waveform is mostly due to the even harmonics that are present in the string vibration. Possibly, when harmonics are present, the effect of the changers in the magnetic field strength are more important.
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Post by ms on May 8, 2021 10:26:13 GMT -5
I would say that the pickup is actually a "variable reluctance" device in which part of a fixed* amount of flux supplied by the magnet is diverted away from the rest of the pickup by the string. As the string moves, the amount and distribution of the diverted flux changes so that the amount of flux passing through the coil changes, thereby producing the signal. The problem with variable reluctance as a model is that it gives no information about the distribution of the diverted flux or, if it does, it is only in terms of a minuscule change in the overall flux, virtually impossible to calculate or visualise. Therefore, an alternative model is almost universally adopted in which the string with its induced magnetism is treated as a source. This is legitimate because it is only changes in the magnetic flux that are of importance, allowing the large static background field to be ignored. Magnetic fields can pass through one another without interference. A caveat is that the magnetic properties of the magnet and poles used in the model must be those evaluated at the prevailing large static flux densities. The pickup poles concentrate flux going to the string from the magnets and also, in the model, gather in flux from the magnetised string - to a large extent with steel poles and to a lesser extent with magnets as poles since magnets have quite low permeability to changes in flux when they are magnetised. *The flux available from the magnet is not absolutely fixed in the case of Alnico magnets but the effect of the string on the operating point of the magnet is so small that it may be considered so for all practical purposes. I think the reluctance concept is appealing because of its similarity to the electrical circuit case, but Faraday's law of magnetic induction is the fundamental way of describing how a pickup works because it is derived directly from Maxwell's equations. Simple magnetic circuits involving a nearly closed path of high permeability material with small gaps obey an analog of ohm's law in which reluctance is like resistance. This is a circuit concept in which the three dimensions of space are replaced with two terminal devices, sort of. The "devices" in the pickup magnetic circuit cannot be easily defined, just as the behavior of a 3D medium filled with material with spatially variable resistivity, illuminated by an E field derived from a couple of metal plates attached to a battery, cannot be solved easily with ohm's law. It is necessary to solve a complicated 3D partial differential equation. For the magnetic case it would be necessary to work with an analog of resistivity, maybe call it "reluctivity". But that is more complicated and less intuitive than working with MLoMI, which so easily and naturally applies to the geometry of a pickup magnetic circuit.
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Post by ms on May 8, 2021 7:27:16 GMT -5
The short answer is because the aperture is determined by the poles, and they are narrower than the coil. So when the poles magnetize the string, the part of the string over the poles contributes the most vibrating field pointed down through the coil. This falls off quickly as you move along the string away from the poles. Also, because the pole has permeability, it amplifies the field from the part of the string right above it. Flux passing through the coil, but away from the poles, does not get so amplified. I really appreciate your patience with those of us (me) who are ignorant on such matters. One caveat about your last statement. It sounds like you are describing a perpetual motion machine. How would the field in the strings amplify the field in the poles if the field is emanating from the poles? Wouldn't that create a runaway feedback loop that would eventually engulf the know universe? It is the pole piece that increases the field from the strings. Kind of like the core of an inductor: current in one loop of wire creates a magnetic field that passes through the other loops, inducing a voltage around each. When a high permeability core is present, the induced voltage increases, increasing the inductance. With a pickup, a field generated external to the coil (from the vibrating string) produces a field through the coil, and the permeability of the core increases the voltage induced around each loop of wire.
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Post by ms on May 7, 2021 14:14:05 GMT -5
The short answer is because the aperture is determined by the poles, and they are narrower than the coil. So when the poles magnetize the string, the part of the string over the poles contributes the most vibrating field pointed down through the coil. This falls off quickly as you move along the string away from the poles. Also, because the pole has permeability, it amplifies the field from the part of the string right above it. Flux passing through the coil, but away from the poles, does not get so amplified. I understand how the pole piece can be a dominant effect over the area of the loops alone, but what if you had a standard pole piece, but the coil was six inches in diameter. Wouldn't the sum area of flux change be so wide that is wouldn't see non-cancelling flux change of string segments that are much less than six inches? If the pole piece is still dominant even with a very wide loop, then maybe suppose the pole piece is a ceramic magnet and contributes now permeability. Supposing this is the case, the extra width of a P-90 or a Microcoil would be trivial, but it's the principle of the thing. Yes, if you make the coil too wide you get cancellation, but I think the aperture is still bounded by the pole. You could figure out which part of the aperture gets canceled first as the coil width increases, but is this really of much practical importance?
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Post by ms on May 7, 2021 7:25:08 GMT -5
The aperture is not determined by the width of the coil. I do not see why you are thinking this, but it cannot be true. I know this has been discussed before, but I'm still not sure why this would be. The harmonics are suppressed when you have a receptive field that is so wide that it experiences both positive and negative flux change in tandem, and the two cancel out. The objective then is to have an inductive field that is narrow enough to capture a positive movement would also seeing a corresponding negative movement. How would the wider loops of a wider coil not result in the capture of both positive and negative flux changes of higher harmonics, more so than smaller loops? The short answer is because the aperture is determined by the poles, and they are narrower than the coil. So when the poles magnetize the string, the part of the string over the poles contributes the most vibrating field pointed down through the coil. This falls off quickly as you move along the string away from the poles. Also, because the pole has permeability, it amplifies the field from the part of the string right above it. Flux passing through the coil, but away from the poles, does not get so amplified.
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Post by ms on May 6, 2021 17:36:49 GMT -5
The coil doesn't generate harmonics. It is the non-linear relationship between the position of the string and the amount of flux that it puts through the coil that generates the harmonics. From common experience, the sensitivity of the pickup falls off rapidly as the distance of the string from the pole increases. But this happens over distances that are comparable with the distance the string moves through as it vibrates. There you have the non-linearity. The gain changes during the string movement. Put in a sinusoidal string movement and out comes a voltage which includes harmonics.
That's interesting, but how does it relate to the aperture window of a pickup? Magnetic power decreases by the inverse square law, so whatever magnetism in a string has that much less influence the farther away from the coil, and I already explained that flux lines traveling along the string contribute virtually nothing to the output. I may be misunderstanding something, but it appears you are conflating two unrelated functions. A magnetic dipole has a one over distance cubed function, not squared. (There are no magnetic monopoles.) A collection of dipoles could fall off slowly nearby and then like a dipole far away.
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Post by ms on May 6, 2021 7:14:01 GMT -5
"It’s not the same as flux lines coming in from the side of the string." What matters is the magnetization excited in the string; the string is what moves and causes changing flux through the coil. Of course the result of the flux lines from the magnet producing magnetization in the string when located on the side is not exactly the same as underneath, but it apparently is very close. The magnetization excited in one location of the string affects that in neighboring locations. The result is a "self-consistent" solution in which the geometry of the high permeability material plays a huge role. For example, wind some closely spaced turns around a high permeability toroid, covering only a small part of the toroid. The flux is almost totally confined to the toroid and uniform around it. This looks nothing like the field produced by the coil with no toroid present.
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Post by ms on May 5, 2021 6:59:55 GMT -5
This app should clear up how the magnetic and/or coil aperture width, as well as the pos along the string, etc affects harmonics, but it doesn't address the affects of proximity and coil density: www.till.com/articles/PickupResponseDemo/index.htmlHere's what makes sense to me about string proximity and aperture. The flux lines come out the top of the pole in a funnel shape. The flux lines around the edges of the field hit the string more straight on when that pole is closer to the strings. Those same lines would then hit the string at more of an angle when the pole is further from the string, therby contributing less to the total pickup output. The total magnetic aperture power might then acually become slightly thinner, but I doubt it makes much differnce in magnetic aperture either way. Raising a pole screw within a magnetic insert may have some audible affect on aperture with regard to the total length of the pole, but I think the effect on note timbre is less sigificant than changing the coil height itself has. I only wish BL was here to clear this up, but I know someone who would have opinion on this over at Wilde-gate. Tillman assumes the aperture is the pickup width. He has hedged on that a bit in the last few years. Assuming something does not clear up anything. The string is a high permeability very elongated object, and so the string magnetization is along its length. The direction must switch over the pole. This means that the necessary field from the string magnetization pointing along the axis of the coil is almost entirely over or very near the pole. You cannot get much signal from anywhere else on the string. aquin43 showed that the magnetization pattern of the string has a high degree of symmetry in the direction around the string. He showed that the magnet can be removed from below the string and moved 90 degrees so that the field comes in from the side without changing the output of the pickup significantly.
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Post by ms on May 4, 2021 10:50:08 GMT -5
Can't it be like speaker driver measurement ? Using semi-inductance model of 5 parameters instead of one to get way better simulation results. Even not understanding the science behind, i used it to measure with a artabox with Arta/Limp a 12" subwoofer so that hornresp (modern speaker sim tool) result agree with real life mic measurement. Few (very few) speaker makers gives those parameters on demand, but they measure it in factory, it take few seconds. Those parameters are the only useful when speakers deals with eddy current (mostly subwoofers due to their long voicecoil), but are still interesting for extented bandwith drivers. Shorting rings inside speaker motor allow to reduce a lot intermodulation distortion, and the effect is easy to see directly on impedance curve when used to look at. So that same "inductance" with different semi-inductance parameters (and so different impedance curve) can lead to noticable distortion level/shape/response. Is there something in this direction in pickup modelling knowledge ? Yes, a semi inductor can be modelled as a series of inductors each shunted by a resistor. Zollner illustrates how this arrangement can be used to model a pickup inductance, and hence its impedance, and a similar arrangement with one shunted section (sometimes replaced by a lossy coupled inductor) and one pure section was referred to in the thread "a new model". The data for such a model can only be obtained by measuring the impedance at the pickup terminals, not the response to a magnetic exciter. Then, there remains the shielding effect of the cover and other parts which comes between the string and the coil but doesn't necessarily appear in the impedance. In some pickups this can be an important part of the response.
So a full model can rapidly become very complex and, while it is useful in simulations, it doesn't lend itself to intuitive appreciation of the pickup's possible sound.
I think that modeling an imperfect inductor across a broad frequency range can be important in design work. But not so much for specifying what influences the sound. The impedance of a pickup is low compared to the load at low frequencies. Therefore, unless you work to make it not true, the response of a pickup is flat at low frequencies (once you have allowed for the standard 6db/octave increase). This extends somewhere up into the lower midrange, but the interesting part starts as you approach the resonance, and then above the resonance it all goes away. But there are interesting questions. For example, if a pickup has a lot of eddy currents, can the inductance change enough over the frequency range of the peak to be important? That is, given that the location and width of the peak are important, could the details of the shape, as determined by the change of inductance with frequency, also matter? That might sound like a silly question, but the ear/brain is a really sensitive analyzer in that frequency range.
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Post by ms on May 4, 2021 7:04:44 GMT -5
Specs can also be used to baffle brains... you mentioned something there that reminded me of that right away - I've seen the resonant peak given as a specification. By itself, unloaded resonant peak frequency is a relatively unimportant spec because of the fact that it is mainly influenced by inductance and capacitance, inductance is not altered by the guitar circuit very much but capacitance definitely is. But the capacitance is always significantly overshadowed by the guitar circuit capacitance. Hence inductance by itself, although it is a much simpler data point, is a far more revealing aspect that tells you far more about how it will operate in situ than resonant frequency ever will. But it sounds really knowledgeable and technical so someone can pretend to be giving out specs when in fact almost nothing useful can be learned from it.
If there is ever a useful "lingua franca" that everyone could use to characterize pickups technically, besides the general construction and type, it would be inductance, loaded resonant frequency and loaded Q. A standard load doesn't exist in the industry, around here we kind of settled on 200k/470pF because it's pretty close to most guitar circuits. That would be a problem in an industry that has no governing body or professional association to organize standards (such as IEEE). It's the 2 dimensional map produced by loaded resonant frequency and Q that mainly defines pickup tone differences. Most other specifications and details are inputs into those characteristics. Thus there are often many ways to target the same data point in that space.
But it would be a huge step, really the first step, if manufacturers would begin listing the inductance and preferably also the frequency at which that is measured (ideally 100/120 Hz, whichever doesn't pick up line noise 50/60 Hz in their country).
Ken man, truer words never spoken ;-) (being "this way inclined" i assure you, i've lost more sales in the day job then i've made from being "overly technical" - so i know exactly where your coming from with it sentiment) I agree entirely on the inductance aspect too - obviously, its an unrealistic expectation for Joe public, but purely from experience with enough pickups, i wager most of us at this end of things, can tell exactly what a pickup is going to be capable of based purely on its inductance and general construction (you know? In very broad strokes) - but, as this threads started to show - even we cant agree on a standard for testing that! (I've always been a 1kHz man myself )
It does beg the question though - is this not a case of "which test frequency is best?" but, rather, a case of "can we all just agree on a frequency to test at?" (and 1kHz is likely the simplest, because its the setting most LCR meters are capable of) - if you do get 2 pickups that do, by some miracle, show the same inductance at 1kHz, then so be it - a bode plot will most likely show a difference within the resonance/Q factor right? I mean, i'm as green as they come to bode plots as a tool for testing, so maybe i'm way off the mark, but that'd be my thinking on it?
I'm actually see stuff in my very preliminary testing that doesn't quite add up to (magnetic spacers on humbuckers are odd - i can see variation on a parametric EQ, you can actually hear a difference on recording (which indicates its a big enough difference to matter!), but that doesn't translate into a change in capacitance, inductance, shift in peak or Q. (although, I'll concede that my testing isn't 100% perfect currently - definitely at the C- stage - must try harder! haha)
Testing and specifying are two different things. An engineer tests a pickup to understand it. You want to test over a brand frequency range in order to understand all the details. But when you make a specification, you want as few numbers as possible, and that means they must emphasize what is most important in determining the sound of the pickup. 3KHz is where the ear-brain works really well. A measurement of inductance at 3KHz includes the effects of eddy currents and so is a better predictor of the resonance frequency than a lower frequency specification. The Q at 3 KHz includes losses resulting from eddy currents and so is a better predictor of the width of the resonance than a lower frequency specification.
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Post by ms on May 3, 2021 9:34:40 GMT -5
That's why it's confusing. A pickup could have a loaded peak at 2kHz, another at 4Khz, and at 3kHz both measure the same despite sounding totally different. Those pickups have different values of inductance; they do not measure the same. They might have the same Q, but it is the difference in inductance that counts for the location of the peak.
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Post by ms on May 2, 2021 18:05:40 GMT -5
If there is ever a useful "lingua franca" that everyone could use to characterize pickups technically, besides the general construction and type, it would be inductance, loaded resonant frequency and loaded Q.
I think that can be expressed as two numbers associated with the inductor: its value and its Q. They should be specified at a compromise frequency in the range where loaded resonances are located, say 3KHz.
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Post by ms on May 1, 2021 12:01:05 GMT -5
No, man. It's a proximity-based thing. The lower to upper harmonic strength increases when any pickup is raised closer to the strings because the stronger vibrations become more emphasized compared to the weaker ones, same as with a microphone. It is indeed the same basic function. Microcoils have the same aperture as Fender SC's. The magnetic aperture does spread a pickup is lowered, but it also weakens exponentially around the edges as the flux lines become more horizontal, so it's really just the coil width that determines the aperture window, unless there are also vertically aligned magnets outside the coil or something that increase power in the edges of the coil. Aperture induced harmonic cancelations start at a specific range for each string and follow corresponding octaves i.e if it starts in the 4kHz range on one string with a given aperture, it would start in the 1kHz range at 2x the aperture. There is some increase in lower to upper harmonic strength for wider apertures, but it's much less significant than the cancelations. I'll read back over that section and get back on this. The aperture is not determined by the width of the coil. I do not see why you are thinking this, but it cannot be true.
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Post by ms on May 1, 2021 11:41:01 GMT -5
(I can not get the images to post in the right order, but they are labeled air for air, stl for steel and cer for ceramic.) The question remaining from that video is this: why does the ceramic magnet cause the inductance of the pickup to drop relative to no magnet? We can find a plausible answer, but not prove it behind any doubt. First it is important to understand the characteristics of ceramic magnets. We look here: en.wikipedia.org/wiki/Ferrite_(magnet). Under "Hard Ferrites" (meaning permanent magnets) we see these two characteristics: 1. Ceramic magnets are "very permanent", that is, it takes a very high field to affect their magnetization or cause demagnetization. 2. They have high permeability. Well, surely both of these things cannot be true, and so we need to run a test. The only ceramic magnet I have is from a mini humbucker, and since I can measure the impedance of a pickup very accurately, I take one of the mini hb coils and measure the impedance with three "cores": air, steel, and the ceramic magnet. The ceramic magnet is not intended to be used as a core for the coil, but it fits, so why not. Air and steel are for mental calibration, and then we want to see where the ceramic magnet fits in that scheme. So the first two attachments show information derived from the impedances of air and steel. To get this information, the high frequency part of the impedance is used to derive the pickup capacitance by a fitting technique, and then the impedance of this capacitance is "unparlelled" from the while impedance. This is better thought of as subtracting the admittance of the C from the whole admittance, and then converting back to impedance. So the imaginary part of this impedance, call it Zu, is the inductive reactance. It might not increase linearly with frequency because of the effect of eddy currents. Air does not cause eddy currents, and the magenta line, Zu.imag, on the plot for air follows the dashed line (the inductive reactance of Lcoil, the inductance at very low frequencies extended to high frequencies as if it was the true inductance). On the other hand, steel is both permeable and conductive. Lcoil has more than doubled from that of the air core, and the magenta line deviates downward from the dashed line. So what is ceramic like? The plot shows that it is within about 1% of air. So it provides the high microscopic currents to make a strong magnetic field, but otherwise it almost might as well be air. So how can it reduce the inductance of the pickup? It is really very simple, I think. With my Tesla meter I measure the field made by the ceramic magnet and some AlNiCo magnets. (They were actually for a regular humbucker, and so a bit larger, but never mind.) The ceramic is about twice as strong as the strongest AlNiCo. So I think what is happening is that the ceramic magnet moves the steel in the humbucker poles a bit further along the hysteresis curve to where the permeability starts to drop, that is, in the direction of saturation, but not nearly there.
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Post by ms on Apr 29, 2021 15:49:20 GMT -5
Great, so I had that backwards too but that does make more sense now that I think about it more: The eddy currents oppose the change in the magnetic field arond the coils, and weakened field -> lower inductance. I guess I was just trying to make sense of the steel ruler increasing the inductance, but your comment of there just being more steel around the coils (in addition to the pole pieces) would explain it. I also got the sense that the guy in the video doesn't really have a solid grasp of the subject, but couldn't put my finger on it. But it did seem very strange to me that he was talking about the materials of the magnets and their "iron content", which would lead me to believe the effects of the steel ruler and ceramic wouldn't be so different. The result seemed contradictory to me, given what he was talking about. Although I believe AlNiCo contains at least some iron as well? Also, thanks for mentioning saturation and hysteresis curves, i think I'm understanding it better now. A key thing to remember is permanent magnets tend to have low permeability. It sort of goes along with many magnetic domains already lined up and not so easy to change. For example, vacuum has a (relative) permeability of 1. Neodymium magnets, very strong, are 1.05. AlNiCo is typically a few times a vacuum. AlNiCo is high enough so that the effects of putting steel (100+) in contact is not such a simple problem to solve sometimes. This why modeling programs have become so popular. My intuition on these sorts of problems is very approximate, and so I think a bit of computing is a really good thing. AlNiCo materials here: en.wikipedia.org/wiki/AlnicoSimple test to show an effect of magnetic field strength on inductance: Wind a Fender type signal coil pickup using non magnetized pole pieces. Measure the inductance. Magnetize the poles. Measure again.
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Post by ms on Apr 29, 2021 14:53:36 GMT -5
Thanks, That does clear it up quite a bit. So apparently the source of my confusion was that I ignored the pole pieces, and it's the pole pieces that are in an external magnetic field of the pickup magnet. It's been more than a decade since I studied this stuff at uni, and of course we didn't specifically look at guitar pickups. So I was thinking more about the more usual case of current in the coil inducing the magnetic field and how materials around the coil respond to it, obviously the field of the pickup magnet is much stronger. But am I right in thinking that it's the currents induced in the non-magnetized steel ruler which increase the inductance in that case? Also, if you or anyone else can provide more insight as to the results in the video, I'd be interested to learn more. Eddy currents reduce the inductance, not increase it. But if you make the measurement at 120 Hz, the frequency is too low for there to be significant eddy current effects in a pickup. The ruler just adds more steel to the system; exactly how this increases the inductance is a complicated question. I would model a 2D approximation in FEMM to find out. Maybe that guy really does believe what he is saying, but notice that when he told you that the strength of a magnet does not influence the inductance, and to prove that you demagnetize a magnet and then put it back in the pickup, he did not actually do that test. For example, a very strong magnet saturates the cores, or at least gets to a flatter part of the curve, reducing their permeability maybe to just about one, and thus decreases the inductance relative to a weaker magnet. It is all in the set of hysteresis curves. Certainly the strength of the field does influence the inductance, and by not understanding what he is doing and selecting results carefully, he can get results that reinforce his lack of understanding. This is, after all, a complicated subject.
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