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Post by antigua on Oct 7, 2016 0:02:48 GMT -5
www.seymourduncan.com/pickup/pearly-gates-set Seymour Duncan says of this model " Seymour discovered Billy’s bridge pickup had slightly more output than most P.A.F.s, which helped to give it the extra drive that make this pickup so special." This model dates waaaay back to 1979, which also happens to be the year of my introduction, as well. A simpler time when an overwound PAF was "so special". This pickup appears to use the same components as the Seymour Duncan '59, with plastic spacer and the like. According the specs, the bridge is hotter than the Seth Lover Bridge by about .33 henries, with a peak resonance that is very close, without a cover. The neck pickups appear to be nearly identical, spec wise. Both sets also use AlNiCo 2 bars, though I measured a higher Gauss at the slug and screw tops of the neck pickup for whatever reason. Seymour Duncan Pearly Gates Bridge, no cover, 4 cond., mfd 2014
Series resistance: 8.31k ohms
Series inductance: 5.097H
Gauss: 290G slug, 310G screw , AlNiCo 2
Unloaded: V: 5.6dB f: 6.29kHz (black)
Loaded (200k & 470pF): V: 2.2dB f: 2.64kHz (red)
Seymour Duncan Pearly Gates Neck, no cover, 4 cond., mfd 2014
Series resistance: 7.27k ohms
Series inductance: 4.151H
Gauss: 360G slug, 340G screw , AlNiCo 2
Unloaded: V: 5.3dB f: 6.89kHz (green)
Loaded (200k & 470pF): V: 2.4dB f: 3.03kHz (gray)
Bode plot: 
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Post by pablogilberto on Oct 17, 2020 23:26:58 GMT -5
Hello!
I want to know what's the difference of using A2 vs A5 magnets for PAF / humbucker styles?
What is the effect in the inductance, resonant frequency and voltage output?
For example, given a PAF with A5 and then changing the magnet to A2 or vice versa.
Is the result similar to when the magnets are the poles like Strat single coils?
Thanks!
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Post by antigua on Oct 18, 2020 1:57:28 GMT -5
Hello! I want to know what's the difference of using A2 vs A5 magnets for PAF / humbucker styles? What is the effect in the inductance, resonant frequency and voltage output? For example, given a PAF with A5 and then changing the magnet to A2 or vice versa. Is the result similar to when the magnets are the poles like Strat single coils? Thanks! Since the bar magnet isn't in the core of the coils, it has a much smaller impact on the inductance. Changing from A5 to A2 only increases the inductance about 20mH, or 0.02H. The measured Gauss usually drops from around 300 to 350G for AlNiCo 5, down to around ~250G with AlNiCo 2. Just considering the facts, the primary effect is that you get less magnetic pull on the strings, and slightly less output. A lot of guitarists on the internet have imaginative descriptions about how A2 and A5 bar differ, as well as rough cast, AlNiCo 3,4 and ceramic magnets, but I think all of that serves to demonstrate that a very minor difference can seem like a very big change when the imagination gets involved, and people exchange their imaginings with other people on the Internet. |
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Post by pablogilberto on Oct 18, 2020 3:07:45 GMT -5
Thanks for this!
I have watched some video of changing a humbucker pickups from A5 to A2, and it seems that there is really a noticeable difference. Where do you think can we attribute that change in tone or response?
How about the case of strat pickups where the poles are the magnets? Is it similar or are we expecting a more pronounced change?
What is the relationship between the magnets permeability and inductance of the coil and its output voltage?
I want to study this further. Can you share some links to read?
Thank you!
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Post by antigua on Oct 18, 2020 9:00:24 GMT -5
Thanks for this! I have watched some video of changing a humbucker pickups from A5 to A2, and it seems that there is really a noticeable difference. Where do you think can we attribute that change in tone or response? How about the case of strat pickups where the poles are the magnets? Is it similar or are we expecting a more pronounced change? What is the relationship between the magnets permeability and inductance of the coil and its output voltage? I want to study this further. Can you share some links to read? Thank you! It's the same difference that you'd get from lowering the pickups, it's just two different ways of weakening the magnetic pull and the flux density at the strings. When string pull is reduced, the strings' vibrations decay more symmetrically, since you don't have a magnetic pull stiffening one half of the string. Magnetic pull promotes higher harmonics by promoting the smaller divisions of the string, just like pinch harmonics, but instead of inducing the harmonics with a hard finger tip, it's just a soft magnetic pull, so it's a lot more subtle. If the pole pieces are AlNiCo, like a Strat, the pull is a lot stronger, because the AlNiCo itself is a lot stronger that steel pole pieces with some other magnet underneath. And since the magnet is in the core of the coil, it increases the inductance a lot more. In this experiment guitarnuts2.proboards.com/thread/9039/alnico-pole-piece-comparison , the difference from AlNiCo 5 to 2 was almost 120 mH, or about 5% higher overall inductance for the test pickup, which possibly makes for an audible difference, but not a big difference. The flux density at the pole top of A5 in a Strat pickup is around 1050 Gauss for the G and D pole pieces, and only 700 Gauss for A2, so again, less string pull, more symmetrical string movement, more fundamental and less harmonics. The relationship between inductance and voltage output is a correlation. Inductance and voltage output but increase when there is lower magnetic reluctance (less air and inert material) between the strings and the coil(s). Steel pole pieces and AlNiCo replace air (or plastic) with permeable material, material that supports a magnetic field, which reduces reluctance, therefore increasing the inductance. At the same time, because it increases the "coupling coefficient" between the guitar strings and the coils, more of the "magnetomotive force" of the guitar strings is present in the pickup's coils, and so there is more voltage output. Again, it's the same as if you raise the pickup closer to the strings, you're reducing the amount of air between the strings and the coil, and increasing the coupling coefficient between the strings and the coil(s). This is also the main reason why humbuckers are a lot louder than single coils, all other things being equal, more of the pickup is placed physically closer to the guitar strings. As far as reading, all of this is very closely related to transformer design, but instead of two coils, you have one coil, and the magnetized guitar strings that act similar to a second coil, so if you read up on transformer design, such as this www.electronics-tutorials.ws/transformer/transformer-construction.html , and you conceptualize the pickup and strings as two halves of a transformers, the principles apply. The only thing to keep in might is that the pickup analogy results in a coupling coefficient that is very low, around .01, where as an ideal transformer would have a coupling of "1", so to the extent that pickups and string are like a trasnformer, it has to be though of as an extremely inefficient transformer, where the two coils are far apart, and there is no core in between them. A guy who goes by "Tele Tucson" actually made a working transformer LTSpice model that matches with experimental measurements very closely, so if you just learn all there is to known about transformers, then a lot of what there is to know about guitar pickups will just suddenly make sense. Not just the coupling, but also concepts such as leakage inductance and stray capacitance as well, which are relevant to guitar pickups.  |
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zolko60
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Post by zolko60 on Jan 27, 2024 12:18:02 GMT -5
It's the same difference that you'd get from lowering the pickups Can we revise that after years? I have calculated f res of various magets in the same pickup from yt video presented in that thread: guitarnuts2.proboards.com/thread/9535/magnet-materials-effect-on-inductanceAt C=600pF A2 4.53H 3.05khz A5 4.37H 3.1kHz A8 4.23H 3.16kHz CER 4.09H 3.21kHz So we can expect audible change at least from changing A2 to ceramic magnet. The second issue I have when I check your measured values using a f res formula. 5.097H, 126pF parasitic and 470pF load capacitances should make 2.89kHz resonant frequency, not 2.64kHz. What am I missing here? Can't I directly sum parasitic and load capacitances? My third problem is I measured f res of my old Pearly Gates Bridge. The same DCR, no cover. I have no inductance meter. All the measuring I have done so far using my magnetic exciter, guitars, about 300pF cable and audio interface HiZ input, complied with your measured Fender 57/62 and Vintage Noiseless pickups. In case of Pearly Gates Bridge f res is 3.5kHz. I can imagine something can be wrong with my approach/expertise but almost 1kHz difference is much too much. All my fellow guitarist making only subjective opinions on pickups consider PG as "humbucker for strat" - much brigter than any "regular PAF". At 2.6kHz it is just regular... |
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Post by antigua on Jan 28, 2024 16:57:33 GMT -5
It's the same difference that you'd get from lowering the pickups Can we revise that after years? I have calculated f res of various magets in the same pickup from yt video presented in that thread: guitarnuts2.proboards.com/thread/9535/magnet-materials-effect-on-inductanceAt C=600pF A2 4.53H 3.05khz A5 4.37H 3.1kHz A8 4.23H 3.16kHz CER 4.09H 3.21kHz So we can expect audible change at least from changing A2 to ceramic magnet. The second issue I have when I check your measured values using a f res formula. 5.097H, 126pF parasitic and 470pF load capacitances should make 2.89kHz resonant frequency, not 2.64kHz. What am I missing here? Can't I directly sum parasitic and load capacitances? My third problem is I measured f res of my old Pearly Gates Bridge. The same DCR, no cover. I have no inductance meter. All the measuring I have done so far using my magnetic exciter, guitars, about 300pF cable and audio interface HiZ input, complied with your measured Fender 57/62 and Vintage Noiseless pickups. In case of Pearly Gates Bridge f res is 3.5kHz. I can imagine something can be wrong with my approach/expertise but almost 1kHz difference is much too much. All my fellow guitarist making only subjective opinions on pickups consider PG as "humbucker for strat" - much brigter than any "regular PAF". At 2.6kHz it is just regular... I don't think a change in inductance of 200mH should be oversold, because there is a margin for error in the final resonant frequency due to guitar cable and hookup lead capacitance. I suppose if you are already using the lowest capacitance guitar cable possible, and you still want a higher resonant peak, a magnet swap from A2 to A5 would gain a little more treble, but if you're going in the other direction, added capacitance would make more sense than a magnet swap. There is a difference in magnetic strength, and that can't be affected electrically, it's a physical difference. I shouldn't say swapping the magnet has no effect on the resonant peak, but it's not a big difference, it's not a unique difference, and it's not the best way to alter the resonant peak of a pickup, and at the same time it will effect the magnetic strength, which is the primary function of the magnet, which aside from raising or lowing the pickup, is the only way to vary that parameter. A stronger magnetic field results in more treble, because 1) it creates asymmetry in the guitar string, transferring energy away from the fundamental movement and into the harmonic movement, and 2) I just learned recently, if the stronger magnetic field succeeds at saturating the guitar strings, to where they can magnetize no further, the magnetic field of the guitar string become more focused towards the center, also resulting in more treble. I'm not sure how to best explain it, it was explained here music-electronics-forum.com/forum/instrumentation/pickup-makers/pickup-theory/990050-magnets-in-pickups/page2#post991512 There's a magnetic cancellation in the guitar string above the pole piece, but if they steel is magnetized as complete as it can be, that cancellation area will be more narrow, creating a sharper focus that allows higher / narrower harmonics to be picked up by the coils. Regarding the 2.64kHz loaded peak, I got that directly from the bode plot, I don't have a good explanation for why the bode plot doesn't match calculated values. The bode plot from the Velleman is not super precise, it tests in steps, so to some extent it will "step" over the actual resonant peak. It tends to be the case that the bode plot shows lower frequencies. I have seen this happen with multiple test setups using all different components. The oscilloscope or integrator only add about 10pF to 20pF capacitance. I just present the data as it is and that's how it comes out. Maybe the true peak is actually supposed to be a little beyond the plotted peak. There are two models of Pearly Gates, the Pearly Gates and Pearly Gates Plus, which was made for Fender, IIRC Tim Shaw asked Seymour Duncan for the Pearly Gates Plus. I don't think there is anything about it that makes it better suited for a Strat, technically. According to the story, Tim Shaw liked the Pearly Gates, but wanted a slightly hotter version, and the only difference is that the Pearly Gates Plus has an AlNiCo 5 bar. It amounts to nothing more than marketing, IMO. I think people who buy an HSS Strat are looking for a Gibson-like tone from the bridge, so there's no need to do anything beyond placing a generic Gibson-like humbucker in the guitar. Also in that video, he's using a cheap LCR meter that likely has a fixed test frequency of 1kHz. It's better to test with a meter like the DE-5000 which can offer a low test frequency, 100Hz or 120Hz, so that eddy currents won't interfere with the meter's ability to calculate the inductance. Humbuckers in particular have a lot of eddy currents because of the steel pole pieces. |
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Post by Yogi B on Jan 28, 2024 20:05:14 GMT -5
Regarding the 2.64kHz loaded peak, I got that directly from the bode plot, I don't have a good explanation for why the bode plot doesn't match calculated values. The bode plot from the Velleman is not super precise, it tests in steps, so to some extent it will "step" over the actual resonant peak. It tends to be the case that the bode plot shows lower frequencies. I have seen this happen with multiple test setups using all different components. The oscilloscope or integrator only add about 10pF to 20pF capacitance. I just present the data as it is and that's how it comes out. Maybe the true peak is actually supposed to be a little beyond the plotted peak. The higher value of 2.89kHz that zolko60 gives seemingly comes from: f_0 = \frac{1}{2 \pi \sqrt{L C}} with L = 5.097H & C = 596pF (= 126pF + 470pF), but that's only exact for infinite Q — and, as Q drops the frequency of the resonant peak also drops. If we include the DC resistance of the pickup, R DC (= 8.31k), and the load resistance, R load (= 200k), we end up with the following formula instead: f_0 = \frac{
\sqrt{4 {R_\text{load}}^2 L C - 2 {R_\text{load}}^2 {R_\text{DC}}^2 C^2 - 2 L^2}
}{
4 \pi R_\text{load} L C
}Which, when substituting in the values, gives f 0 = 2.72kHz — quite a bit closer to your measured value. And that's only assuming a 3-part pickup model: the additional parts in the more complex models work to model eddy current losses, thus equate to further damping (lower Q). (For example, to get f 0 = 2.64kHz, we need only tweak the model to include 900kΩ of resistance in parallel to the parasitic capacitance.) |
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Post by JohnH on Jan 29, 2024 3:38:56 GMT -5
Yes in general, for most resonant systems be they electrical, mechanical, accoustic, or the mood swings of an adolescent tree-frog, the addition of damping slightly reduces the frequency of the maximum signal. We can measure this and it comes through in the tests and in analysis models that include such damping.
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Post by ms on Jan 29, 2024 11:38:24 GMT -5
You really need both exciter coil measurements and measurements of impedance versus frequency. Then you need to assemble all that information into a coherent model, and then you can predict what you should measure in a specific set of conditions.
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zolko60
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Post by zolko60 on Jan 29, 2024 12:04:34 GMT -5
![]() I am lost. If 200mH difference is oversold, 200Hz of f res is too, instead gauss at the strings is relevant which can be adjusted by changing height of a pickup as easy as swapping 300pF cable to 600pF... Yet you publish results suggesting 10Hz accuracy knowing you can not measure with such accuracy. And yes, poeople trying to demonstrate difference between pickups probably use the same pickup height, cable and amp settings. If they were matching f res with capacitances to 50Hz and amp gain to pickup output to 0.5dB, it could end in conclusion there is no difference at all. Back to my Pearly Gates Bridge as Ken Willmot amateur method testing in home studio enviroment. I adapted it to my needs. While I like RMAA I want to keep it simple and real time, this is why I use white noise and RTA, knowing that my accuracy is about 100Hz. Here is RTA reading of PGBL sitting in a strat pickguard eguipped with 500k pots, connected with 300pF cable to HiZ input of my audio interface. I use 300pF cable because the results are close to yours in case of Fender 57/62 and VN pickups.  Here are superimposed readings of uncorrected reading and 6dB/oct LP filter. As you may see I cannot determine f res implementing "integrator" this way:  You may say that my capacitance load is wrong, but Ken proposes a method for estimatiting pickup inductance by rising load above cable capacitance matters using 100nF cap. I happen to have 47nF tone cap in my circut so after setting the tone pot to 0ohm value, here what I get:  Now calculating inductance out of f res 340Hz and 47.5nF load I get 4.6H... and my measured f res is still 500-700Hz above Antigua Pearly Gates Neck reading 4.151H... So what is the conclusion? My Pearly Gates Bridge is not Antiqua Pearly Gates Bridge? Or Ken/My measuring method is wrong? Or something else? |
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Post by antigua on Jan 29, 2024 13:45:08 GMT -5
![]() I am lost. If 200mH difference is oversold, 200Hz of f res is too, instead gauss at the strings is relevant which can be adjusted by changing height of a pickup as easy as swapping 300pF cable to 600pF... Yet you publish results suggesting 10Hz accuracy knowing you can not measure with such accuracy. And yes, poeople trying to demonstrate difference between pickups probably use the same pickup height, cable and amp settings. If they were matching f res with capacitances to 50Hz and amp gain to pickup output to 0.5dB, it could end in conclusion there is no difference at all. Back to my Pearly Gates Bridge as Ken Willmot amateur method testing in home studio enviroment. I adapted it to my needs. While I like RMAA I want to keep it simple and real time, this is why I use white noise and RTA, knowing that my accuracy is about 100Hz. Here is RTA reading of PGBL sitting in a strat pickuard eguipped with 500k pots, connected with 300pF cable to HiZ input of my audio interface. I use 300pF cable because the results are close to yours in case of Fender 57/62 and VN pickups. Here are superimposed readings of uncorrected reading and 6dB/oct LP filter. As you may see I cannot determine f res implementing "integrator" this way: You may say that my capacitance load is wrong, but Ken proposes a method for estimatiting pickup inductance by rising load above cable capacitance matters using 100nF cap. I happen to have 47nF tone cap in my circut so after setting the tone pot to 0ohm value, here what I get: Now calculating inductance out of f res 340Hz and 47.5nF load I get 4.6H... and my measured f res is still 500-700Hz above Antigua Pearly Gates Neck reading 4.151H... So what is the conclusion? My Pearly Gates Bridge is not Antiqua Pearly Gates Bridge? Or Ken/My measuring method is wrong? Or something else? I put the values as shown on my LCR meter or the Velleman output. I'm not saying 200mH is irrelevant in terms of pickup testing, more that it's irrelevant when it comes to making a purchase decision about guitar pickups. If you have two pickups and they have an inductance that's within 200mH, then it's effectively the same pickup, because the difference in frequency will fall within a window of variance that you get from varied cable capacitance. If the difference is inductance is more significant, then it will surpass the difference expected from different lengths of guitar cable. For example, 3H and 500pF comes out to 4.1kHz, but change that to 1000pF, the frequency drops to 2.9kHz. But if you start with 3H and 500pF, jump to 3.2H, the frequency only drops from 4.1kHz to 4.0kHz. The precision or lack of is just an artifact of the measuring tools. Even though people test pickups with a given rig, it's never the less the case that it's easier to modify the rig than it is the pickup. At the end of the day I do pickup testing for practical reasons, so I think a lot about whether a difference is audible or not. Almost every pickup I've tested I ended up using in a guitar for some period of time. I've only ever bought two or three solely to measure their values. All of this is a necessity thing for me, the pickup makers don't provide this information so I couldn't make informed buying decisions. I've mostly come to the conclusion that the market is saturated with near identical pickups with trivial electrical variation, and that much of the time the right move was probably not to buy new pickups at all. I personally haven't derived inductances from swamping the pickup with a known capacitance, I almost always use the DE-5000 or the Extech 380193, set to 100Hz or 120Hz, because it's just way faster. I believe you have to unsolder your pickup from your guitar to the unloaded peak frequency, because the guitar cable and the control pots are going to add variables that are harder to account for and lead to confusing errors. I never measure guitar pickups with them still connected to the guitar, too much variability to work around. Add to this that the pot and cap values are nominal, they tend to have a 10% margin for error, so you would have to measure the true values of the pots and caps before solving for them in the peak resonant calculation. Ken knows a lot more about this than I do, both the process of solving for inductance with a known large capacitance, and using an computer's audio interface for testing. I've stuck with USB oscilloscopes and LCR meters myself. Something else I can speak to from testing though is that even though the DC resistance varies easily from one pickup to another, the inductance tends to be very consistent because the pickup manufacturer set their machines to a specific turn count, and the inductance will follow closely with the turn count. If your purpose here is to make sure your Pearly Gates was manufactured correctly, I'd say there's little doubt that it is. I might check the inductance if I though it were a counterfeit, and I wanted to see how close the possible counterfeit's inductance is to the real thing. |
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zolko60
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Post by zolko60 on Jan 29, 2024 14:17:28 GMT -5
This is why I started to go down a rabbit hole of pickups research. No specs, useless user opinions, myths, fairytales... Now I have come to the point my measuring do not give me any reliable results or at least comparable with other people measurements, what scares me  I came to this forum, hoping for some help.  I have hypothesis that my probe still having ferrite core which permability is lower than air is an issue, but why it distorts readings of only a few humbucking pickups to such extent? BTW I tried different probe inductors. Ken suggested fluorescent lights ballast. One of them apeared to be 10nF cap and the second one a coil made of aluminium stripe did not propagate anything to be analyzed. 500mH wah-wah inductors did not work either. I was just lucky to find a small transformer that does a job. I hope there must ba a way to reliably measure pickups in situ and I believe such approach while not offering a great accuracy, is better because one can test the whole RLC network not only a pickup and it is what user is hearing. BTW2 listening to white noise modulated by guitar filter is very nice experience. |
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Post by Yogi B on Jan 29, 2024 18:16:03 GMT -5
Here are superimposed readings of uncorrected reading and 6dB/oct LP filter. As you may see I cannot determine f res implementing "integrator" this way: The slope of that filter is closer to 4dB/oct. After playing around with Pro-Q, I think I've made sense of the GAIN knob's behaviour when using the "Flat Tilt" filter. It's not consistent: at minimum gain (supposedly -30dB) the slope is actually -20dB/decade (approx. -6dB/oct), but only when the FREQ knob is set below around 600Hz. Without warning above that the slope is made progressively shallower — down to around -9.5dB/decade (-2.8dB/oct) when FREQ is set at maximum (30kHz). Seemingly this is to keep the boost level at 20Hz capped to a maximum of 30dB, so as not to become too loud. (I've also verified that this isn't just a graphical glitch by feeding white noise through Pro-Q then into another spectral analyser.) |
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zolko60
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Post by zolko60 on Jan 29, 2024 18:36:00 GMT -5
Does it matter? I only wanted to demonstrate flat tilt filter does not help. Ken does not claim using integrator makes a difference in determining f res but it makes a look of bode plots right.
I can apply tilt filter to affect white noise feeding a probe but I do not believe it would look any different.
Please tell me, do you believe the measurement of f res can be reliable carried in situ?
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Post by antigua on Jan 29, 2024 22:44:57 GMT -5
This is why I started to go down a rabbit hole of pickups research. No specs, useless user opinions, myths, fairytales... Now I have come to the point my measuring do not give me any reliable results or at least comparable with other people measurements, what scares me I came to this forum, hoping for some help. I have hypothesis that my probe still having ferrite core which permability is lower than air is an issue, but why it distorts readings of only a few humbucking pickups to such extent? BTW I tried different probe inductors. Ken suggested fluorescent lights ballast. One of them apeared to be 10nF cap and the second one a coil made of aluminium stripe did not propagate anything to be analyzed. 500mH wah-wah inductors did not work either. I was just lucky to find a small transformer that does a job. I hope there must ba a way to reliably measure pickups in situ and I believe such approach while not offering a great accuracy, is better because one can test the whole RLC network not only a pickup and it is what user is hearing. BTW2 listening to white noise modulated by guitar filter is very nice experience. The DE-5000 can be had for about $100 to $130, depending on where the best deal is. I think it's a good investment. It can also measure capacitance at 100kHz in Cp mode, and that's good for testing cables and other components as well as pickup, and it even has a DCR settings. It's really a one stop shop meter for our needs. I've acquired some pricier LCR meters that do one thing better, but none of them are as well rounded. And then there's the WT10A magnetometer for only $80 on Amazon. The price on that has come down, it used to be over $100. Most electronics from China have increased in price lately, so that's a nice surprise. With those two meters alone you can know most all you want to know about any given pickup. The main thing you lose out on if you forego bode plots is studying eddy currents by seeing how the impedance curve changes, lets say; with or without a metal cover on the pickup, or determine what sort of metal the cover is made of based on the Q factor of the bode plot. That's more about experimentation than gathering data for existing production pickups, because usually the type of metal, and the eddy current profile for a given pickup on the market will be known or easy to guess. The DE-5000 also has a Q measurement, so technically it has the capacity to illuminate about eddy current losses, but that's an ongoing project, trying to figure out what test frequencies and test scenarios result in usable information. Sadly the Velleman USB oscilloscope I like to use is no longer manufactured, and not good replacement exists on the market, except maybe the Digilent Discovery 2. A computer audio interface is probably the best bet now, but I haven't had a need to go that route since my Velleman is still functional. For a probe inductor, you can just buy some fine magnet wire and wrap it around a popsicle stick, here's a pic of mine guitarnuts2.proboards.com/thread/7890/coil-productivity-respect-permeability-proximity , I used some leftover 42AWG wire. You can take off of some cheap guitar pickup. About a hundred wraps will give you a good exciter, but you can wrap it two or three hundred times and have a really good test probe. The self-resonance of the test probe needs to just be much higher than that of the guitar pickup itself. With a DE-5000 you could quickly see what the inductance happens to be of any test probe you create, maybe a hundred henries, but no matter what, it's going to be a small fraction of what you see with the guitar pickup under test. If you are interested in seeing the sound as you hear it, then in situ is good, but you just have to keep in mind that it's a more complicated network than a simple three part RLC model, because you have the capacitance of the cable, and the capacitance of the pickup's own connection cable, and the load resistance of the pots in between those two sources of capacitance. As mentioned above by Yogi B, the math is more complex. |
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Post by antigua on Jan 29, 2024 22:51:49 GMT -5
Please tell me, do you believe the measurement of f res can be reliable carried in situ? You're using a guitar cable right? I would instead unscrew the jack plate of the guitar, pull it out, and connect alligator clips to the female end guitar jack, so that there is no guitar cable involved. That should produce a much better result. |
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Post by ms on Jan 30, 2024 9:46:19 GMT -5
"...ferrite core which permability is lower than air is an issue"
Air is about the same as vacuum and you cannot go any lower than that. Ferrite can have a permeability from somewhat greater than vacuum to many thousand times greater. In general, ferrite permanent magnets have low permeability, and the many types that do not have significant permanent magnetism vary widely. I prefer to use a very small air core exciter that can illuminate a single pole piece as the string does. (You need good SNR in the measurement setup.)
For in situ, if you do not like Antigua's method, a short Low C cable can be not too much worse. The idea is to keep good sensitivity at high frequencies, although this is not as much of a problem as it might seem since the law of magnetic induction depends on the time rate-of-change of the signal.
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Post by ms on Jan 30, 2024 12:39:43 GMT -5
"I was just lucky to find a small transformer that does a job."
What kind of transformer is this? Transformers are usually designed to keep flux in their own local magnetic circuit. An exciter coil is designed to send flux through the pickup coil. All transformers have some leakage flux that escapes the local circuit, but it might not be much, and I suppose that it is possible it could affect your frequency response.
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zolko60
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Post by zolko60 on Jan 30, 2024 13:19:01 GMT -5
I took ferrite core off my probe and constructed jig 470pF cap paralell with 470kOhm resistor connected with 5cm cable to 1/4 jack. Jack goes to Boss Metal Zone as a buffer and then to my audio interface. I guess Metal Zone should have 1Mohm load. Swamping cap was 47nF connected when used. My probe transformer has 5ohm winding with central tap and second winding of 0.3ohm. I use only 5ohm winding serial with 100ohm resistor. It looks almost the same as Ken Willmott presents. Then I measured my reference 57/62 strat pickup, some other strat pickups as well as three humbuckers. Here are the results: | Pickup | DCR (kohm) | f res @470pf (kHz) | f res @47.5nF (Hz) | calculated* L (H) | | Fender 57/62 | 5.9 | 4.1 | 500 | 2.2 | | Pearly Gates Bridge | 8.2 | 3.4 | 340 | 4.6 | | Gibson BurstBucker2 | 8.3 | 3.1 | 340 | 4.6 | | SD SJBJ Bridge | 15.6 | 2.0 | 250 | 8.5 |
* I used simplified f res formula with 1/sqrtLC Conclusion: If Antigua measued pickup values are correct, my implementation of Ken Willmott method in case of measuring humbuckers are giving false results while delivering excellent results with single coils. In situ or not does not matter. |
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Post by ms on Jan 30, 2024 13:55:02 GMT -5
I took ferrite core off my probe and constructed jig 470pF cap paralell with 470kOhm resistor connected with 5cm cable to 1/4 jack. Jack goes to Boss Metal Zone as a buffer and then to my audio interface. I guess Metal Zone should have 1Mohm load. Swamping resistor was 47nF connected when used. My probe transformer has 5ohm winding with central tap and second winding of 0.3ohm. I use only 5ohm winding. It looks almost the same as Ken Willmott presents. Then I measured my reference 57/62 strat pickup, some other strat pickups as well as three humbuckers. Here are the results: | Pickup | DCR (kohm) | f res @470pf (kHz) | f res @47.5nF (Hz) | calculated* L (H) | | Fender 57/62 | 5.9 | 4.1 | 500 | 2.2 | | Pearly Gates Bridge | 8.2 | 3.4 | 340 | 4.6 | | Gibson BurstBucker2 | 8.3 | 3.1 | 340 | 4.6 | | SD SJBJ | 15.6 | 2.0 | 250 | 8.5 |
* I used simplified f res formula with 1/sqrtLC Conclusion: If Antigua measued pickup values are correct, my implementation of Ken Willmott method in case of measuring humbuckers are giving false results while delivering excellent results with single coils. In situ or not does not matter. 1/sqrtLC is more accurate for Fender single coils because they use Alnico magnet cores, which have lower eddy currents than the steel used in humbuckers . I suppose that if you wanted verify if this is a factor in your measurements you might measure a P-90, single coil but steel cores, or one of those cheap strat pickups with steel cores. Why do you need the Boss pedal? You should have plenty of gain with the instrument input of your audio interface. Yes the metal zone is 1 M input impedance according to a schematic I found somewhere. But does it have flat enough frequency response? The circuit is complicated, and I did not figure it all out. |
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zolko60
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Post by zolko60 on Jan 30, 2024 14:10:12 GMT -5
While I don't have inductance meter, I use Ken's swamping cap method for calculating inductance. I care about f res values I can see on ProQ3 RTA with accuracy of 100Hz in 3-4kHz area and 10Hz in 200-600Hz area. If I use the second formula posted by Yogi B I probably will get better estimation of inductance but my observed f res will not change. f res is still too high with respect to Antigua values in case of all humbuckers. I need a stomp box buffer for a practical reason of not having to keep my jig on my RMA FF400 interface (and my interface load is 470kohm so I don't see sharp enough peak on RTA) |
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Post by JohnH on Jan 30, 2024 16:23:56 GMT -5
I think that trying to get a clear single meter reading of inductance on a pickup is subject to some plus or minus depending how its done. This is because any equivalent circuit that properly captures its real response will not be a single simple inductance, but it will be more complex. That being said, it's still a really useful parameter if done consistently.
But it may not correspond exactly to L values back calculated from bode plots, and its not necessarily a reflection on either method.
One shift that happens, when assessing a real pickup with eddy effects and damping with bode plots, is a result of integrating. The integration definitely is the best way to present results because it evens out the curve, and where there are no particular effects happening, gives a flat response.
But the act of integrating effectively rotates the curve by 6dB per octave. So if the response is a real one with a rounded peak, it's rotating the top of the hill! So the place that was just before the peak pre-integration, is now at the peak, and its a slightly lower frequency. If there was a perfectly undamped peak of very high Q, as predicted for LC resonance by the simple equation, the peak is so sharp that this shift doesn't occur.
Also as noted before, any damping does tend to reduce the frequency of the maximum response in a resonant system.
And why integrate? If the bode plot is raw with a frequency sweep of constant magnitude, it tends to rise. Integrating it flattens it out for neutral responses. This actually matches well with real strings. In a theoretical perfectly balanced string set, all of equal tension when tuned, the added moving metal in the lower strings compensates for less induction at lower frequency and we get about the same magnitude of response by plucking each string, (then subject to all the interesting quirks that we are investigating)
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Post by antigua on Jan 30, 2024 17:40:20 GMT -5
One shift that happens, when assessing a real pickup with eddy effects and damping with bode plots, is a result of integrating. The integration definitely is the best way to present results because it evens out the curve, and where there are no particular effects happening, gives a flat response. But the act of integrating effectively rotates the curve by 6dB per octave. So if the response is a real one with a rounded peak, it's rotating the top of the hill! So the place that was just before the peak pre-integration, is now at the peak, and its a slightly lower frequency. If there was a perfectly undamped peak of very high Q, as predicted for LC resonance by the simple equation, the peak is so sharp that this shift doesn't occur. This is what I was thinking but couldn't put into words. I can set up the integrator later and do two plots, one off and one on, and see how the peaks vary. |
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zolko60
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Post by zolko60 on Jan 30, 2024 17:40:41 GMT -5
If 6dB/tilt is needed, it may place f res 100-200Hz lower at 2-4kHz range and it makes white noise/RTA method inaccurate cause only knee is observed what I have presented. The difference is much greater, about 800Hz and it is consistent between my readings and Antigua measurements concerning only humbuckers (excluding stack humbucker - Fender Vintage Noiseless).
I will wind couple of new exciter coils to check if they are to blame.
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Post by ms on Jan 30, 2024 18:19:38 GMT -5
I think taking out the 6 db per octave slope gives the correct value of the resonance. What you need is a flat test signal to get the right answer for the values of the electrical components.
I also think that the correct inductance is what you measure at low frequencies, say 100 Hz, below the frequency range where eddy currents matter much. Then it is consistent with the math to look at the shift in resonant frequency from the "simple" value as a result of additional components in the circuit, which have a significant effect in the few KHz range..
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zolko60
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Post by zolko60 on Feb 1, 2024 15:53:07 GMT -5
This time I filtered outgoing white noise with Pro Q3 applying two filters: 6dB/oct flat tilt at 1400Hz and 96db/oct low cut at 110Hz to get rid of bass overdriving my output. Double checked if what returns is not overdriven by listening to sine signal and watching harmonic content on RTA. Looks better than expected but still not expected values. With that filter applied I cannot observe any peak with swamping 47nF cap. I can rise input impedance to 1Mohm but as I understand resistive load helps dumping and lowers f res. I don't understand why integrator impedance is 10Mohm and what voltage divider is needed for. Maybe that serial resistance helps you find home?  |
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I came to this forum, hoping for some help. 