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Post by antigua on Dec 9, 2016 14:00:25 GMT -5
There was a conversation on another forum going about AlNiCo pole pieces, so I got out a dummy coil and measured the inductance in a plastic Strat pickup with these different AlNiCo grades popped in:
material inductance pole piece len. peak resonance with 570pF
Steel 3.975H 0.66" -.74" 3.34kHz
AlNiCo 2 2.203H 0.68" 4.49kHz
AlNiCo 3 2.244H 0.67" 4.45kHz
AlNiCo 4 2.184H 0.71" 4.51kHz
AlNiCo 5 1.882H 0.68" 4.86kHz
Air 1.493H n/a 5.46kHz
The steel poles here are taken from a Japanese ceramic pickup found in a Japanese Fender. These differences all owe to permeability, and if we assume some amount of capacitance, say 570pF, a peak resonance can be predicted. Steel is a lot more permeable than any of the AlNiCos.  Bode plots:Here are some bode plots made with a driver coil, an integrator and a USB oscilloscope:  Test pickup details: (it's a ceramic Fender MIJ pickup with the magnet and slugs removed) Inudctance: 1.493H 120Hz, 1.506H @1khz (air core) DC Resistance: 5.44k ohms Driver details: (its wrapped around the end of a popsicle stick) Input voltage: 5.0Vpp 1.77 VRMS Inductance: 0.712mH @ 120Hz, 0.698mH @1khz DC Resistance: 53.0 ohms Wire gauge: 41AWG Dimensions LWH: 0.39" x 0.12" x 0.34" The driver coil is placed above the "D" pole piece. All of the pole pieces were flush with the plastic bobbin, and all six holes contain the given core type. The distance between the bottom of the driver coil and the top of the pole piece was 0.1". Raw numbers: Hz Vrms dBVAlNiCo 2
100.0 2.451 7.788
1000.0 2.592 8.273
2000.0 2.724 8.706
3000.0 2.990 9.513
4000.0 3.501 10.884
5000.0 4.352 12.774
6000.0 6.343 16.046
7000.0 11.664 21.337
7500.0 13.769 22.778 peak
8000.0 10.309 20.264
9000.0 4.708 13.457
10000 2.749 8.783
12000 1.385 2.830
AlNiCo 3
100.0 2.657 8.487
1000.0 2.802 8.948
2000.0 2.965 9.440
3000.0 3.251 10.240
4000.0 3.743 11.464
5000.0 4.639 13.328
6000.0 6.695 16.516
7000.0 11.093 20.901
7500.0 11.979 21.568 peak
8000.0 9.201 19.276
9000.0 4.627 13.305
10000 2.809 8.972
AlNiCo 4
100.0 2.494 7.939
1000.0 2.637 8.423
2000.0 2.787 8.904
3000.0 3.056 9.702
4000.0 3.548 11.000
5000.0 4.390 12.849
6000.0 6.320 16.014
7000.0 11.156 20.950
7500.0 12.950 22.245 peak
8000.0 9.989 19.990
9000.0 4.740 13.515
10000 2.796 8.931
12000 1.411 2.989
AlNiCo 5
100.0 2.178 6.762
1000.0 2.312 7.281
2000.0 2.424 7.690
3000.0 2.597 8.289
4000.0 2.950 9.396
5000.0 3.581 11.079
6000.0 4.794 13.613
7000.0 8.177 18.252
8000.0 15.136 23.600 peak
9000.0 6.470 16.218
10000 3.332 10.455
12000 1.569 3.913
Steel
100.0 4.290 12.649
1000.0 4.298 12.664
2000.0 4.439 12.946
3000.0 4.967 13.923
4000.0 6.122 15.738
5000.0 8.336 18.419
6000.0 11.459 21.183
6100.0 11.384 21.126 peak
7000.0 7.891 17.943
8000.0 4.454 12.975
9000.0 2.766 8.836
10000 1.968 5.879
12000 1.168 1.348
Air
100.0 1.797 5.092
1000.0 1.869 5.434
2000.0 1.937 5.743
3000.0 2.038 6.183
4000.0 2.236 6.989
5000.0 2.529 8.060
6000.0 3.151 9.969
7000.0 4.406 12.881
8000.0 7.992 18.053
9000.0 18.863 25.512 peak
10000 5.904 15.423
12000 1.877 5.468
Normalized bode plot (at 1kHz):  |
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Post by ms on Dec 10, 2016 7:35:00 GMT -5
When you measure the the resonant frequencies, you might run into an interesting effect: that the resonant frequency of the coil using steel cores is higher than you would predict when using the inductance measured at a frequency well below the peak. This is caused by eddy currents, and so it is much bigger at high than medium frequencies, and so you might not see it so much when measuring with a C across the coil. But I show an unloaded case here. The top plot shows the coil with alnico magnets. The inductance is derived from the measurements at low frequencies, and the dashed line is the impedance that inductance would give as a function of frequency (its imaginary part). The C is derived from the measurement with a fitting technique using the high frequencies, and then its effect is removed from the total impedance, leaving the yellowish and green lines, in order to show the effects of eddy currents. Notice that the yellowish line and the dashed line are the same at guitar frequencies, and show a small difference at higher frequencies. Eddy currents from alnico are small. Now look at the bottom plot, for steel cores. The yellowish line is well below the dashed line even at guitar frequencies, indicating a big effect of eddy currents. The ratio of low frequency inductances implies that the resonance should be a bit over 9 KHz, but it is over 11 KHz. It is not the low frequency inductance that applies, but rather an "effective" inductance based on the value of the imaginary part of the impedance at higher frequencies. That is, the impedance is not as high as one would expect based on the value of the low frequency inductance, and so the resonant frequency moves up. Note that the real part of the impedance is well above the coil resistance, and so the Q is lower than one might expect also. The shape of the peak is somewhat affected, I believe.  |
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Post by stratotarts on Dec 10, 2016 8:39:00 GMT -5
Welcome to the board. It is important to have as many different investigators bringing different approaches to the subject, in order to add a strong measure of verification to the studies. The online history of pickup investigation includes a number of "lone wolf" experimenters that sometimes got sidetracked because of the lack of peer review and support. I was one. This post is very interesting, but I think you will need to give more background and detail of your investigation, or nobody will be able to understand it. As I do not have any idea what your experimental setup is, I find it difficult to separate theoretical statements from actual observations. This is not intended as a criticism of your comments, as they are more than welcome. It's just that the context that makes them clear to you, may not be shared by many people (even) here. I measured the inductance of the SH1n at different frequencies here: thread link and it looked like the inductance does not vary much. Do my measurements not cover a wide enough frequency range to detect the effect you're talking about? The least-squares fitting that Dan Carson did ( link) found no increasing inductance above 1 kHz. |
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Post by ms on Dec 10, 2016 11:29:41 GMT -5
Welcome to the board. It is important to have as many different investigators bringing different approaches to the subject, in order to add a strong measure of verification to the studies. The online history of pickup investigation includes a number of "lone wolf" experimenters that sometimes got sidetracked because of the lack of peer review and support. I was one. This post is very interesting, but I think you will need to give more background and detail of your investigation, or nobody will be able to understand it. As I do not have any idea what your experimental setup is, I find it difficult to separate theoretical statements from actual observations. This is not intended as a criticism of your comments, as they are more than welcome. It's just that the context that makes them clear to you, may not be shared by many people (even) here. I measured the inductance of the SH1n at different frequencies here: thread link and it looked like the inductance does not vary much. Do my measurements not cover a wide enough frequency range to detect the effect you're talking about? The least-squares fitting that Dan Carson did ( link) found no increasing inductance above 1 kHz. It is all observation, direct, followed by data analysis from the impedance vs. frequency measurements. The dashed type lines are low frequency results extended across frequency. Measuring pickup impedance with an A/D recording interface Software for performing pickup analysis with a recording interface.
My 59n measurements are attached.  You can see that the inductance does vary. My method eliminates any significant effect from cable capacitance. I think that is why my resonance measurement is higher than yours. I think you are misreading Dan Carson's frequency scale. It is Hz times 10^4, not 10^3. He shows variation up to about 10 KHz. The total least squares fitting approach is nice if you really have confidence in your model. I prefer to use fitting only where necessary, such as to get a really good capacitance measurement, necessary for seeing how the effective inductance varies with frequency. |
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Post by stratotarts on Dec 10, 2016 12:05:58 GMT -5
Thank you. That does look very interesting indeed. But, I can't find your system diagram. In the post that you linked to, there is only this:
"The version used for these tests is shown here (p1010005.jpg). The jpg file is not accessible to me, although I admit it could be a browser issue. Have you considered consolidating the documentation in a stand alone document? Perhaps posting it here?
I didn't misread Carson's chart. I'm ignoring the slight rise between 10k and 1k.
It's doubtful that I have erred in estimating cable capacitance. It's an issue that we have been dealing with for almost a year.
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Post by stratotarts on Dec 10, 2016 12:30:52 GMT -5
I'm still not sure what you mean, "you can see that the inductance does vary". I don't see anything like that on the chart. I have an SH-1 in front of me now, and I can confidently test the inductance using the swamping capacitor method. I did this using a 4.7nF and a 0.063uF cap, which produced peaks at 1130 and 315Hz, respectively. The results of the inductance calculations from that, are 4.14H and 4.03H. That is only a 3% difference.
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Post by ms on Dec 10, 2016 12:35:17 GMT -5
Thank you. That does look very interesting indeed. But, I can't find your system diagram. In the post that you linked to, there is only this: "The version used for these tests is shown here (p1010005.jpg). The jpg file is not accessible to me, although I admit it could be a browser issue. Have you considered consolidating the documentation in a stand alone document? Perhaps posting it here? I didn't misread Carson's chart. I'm ignoring the slight rise between 10k and 1k. It's doubtful that I have erred in estimating cable capacitance. It's an issue that we have been dealing with for almost a year. Are we looking at the same thing? I see most of the inductance drop between 1 and 5K. This is the results for the old lap steel P-90 we are discussing? |
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Post by ms on Dec 10, 2016 12:56:41 GMT -5
I'm still not sure what you mean, "you can see that the inductance does vary". I don't see anything like that on the chart. I have an SH-1 in front of me now, and I can confidently test the inductance using the swamping capacitor method. I did this using a 4.7nF and a 0.063uF cap, which produced peaks at 1130 and 315Hz, respectively. The results of the inductance calculations from that, are 4.14H and 4.03H. That is only a 3% difference. The imaginary part of the impedance with the effect of the capacitance removed is not a straight line, but rather is below it, increasingly so with increasing frequency. Therefore the effective inductance is less than the low frequency inductance. This is consistent with the apparent "anomaly" in resonant frequencies. I agree that there is not much drop between low frequencies and 1 KHz. |
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Post by ms on Dec 10, 2016 13:01:55 GMT -5
Thank you. That does look very interesting indeed. But, I can't find your system diagram. In the post that you linked to, there is only this: "The version used for these tests is shown here (p1010005.jpg). The jpg file is not accessible to me, although I admit it could be a browser issue. Have you considered consolidating the documentation in a stand alone document? Perhaps posting it here? I didn't misread Carson's chart. I'm ignoring the slight rise between 10k and 1k. It's doubtful that I have erred in estimating cable capacitance. It's an issue that we have been dealing with for almost a year. The diagram is almost too simple to draw. Put a 1K resistor between one lead of a pickup and ground. The junction is one sampled channel. Drive the other end of the pickup with the exciting source. Take the other sample at this point. In the processing, subtract the first sample stream from the second. You now have the voltage across the pickup, and a voltage proportional to the current through it. Fourier analyze, etc. |
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Post by stratotarts on Dec 10, 2016 13:19:14 GMT -5
I'm still not sure what you mean, "you can see that the inductance does vary". I don't see anything like that on the chart. I have an SH-1 in front of me now, and I can confidently test the inductance using the swamping capacitor method. I did this using a 4.7nF and a 0.063uF cap, which produced peaks at 1130 and 315Hz, respectively. The results of the inductance calculations from that, are 4.14H and 4.03H. That is only a 3% difference. The imaginary part of the impedance with the effect of the capacitance removed is not a straight line, but rather is below it, increasingly so with increasing frequency. Therefore the effective inductance is less than the low frequency inductance. This is consistent with the apparent "anomaly" in resonant frequencies. I agree that there is not much drop between low frequencies and 1 KHz. Page 7, Least Squares Fit Parameter Results, upper left chart, "L-fit (henries)" vs. frequency. The inductance appears to peak at about 7H somewhere very low (the expanded scale makes it hard to interpret). It looks like it might be about 100 Hz. At 5kHz it has dropped to about 5H. Above that, there isn't much change. I don't have a P90 in particular to test, but assuming a self resonant frequency of about 8k and a loaded resonant frequency of about 3k (typical PAF) , from that chart the only difference would be about (5.2-4.7)H = 0.3H. I see how that would alter the resonant frequency, but I'm not grasping the importance. If the estimate for L at self-resonance is high, the only consequence that I can see, is that the capacitance might be underestimated. But in the application of that data, which normally is understanding how the pickup will perform in circuit, the self capacitance is usually a relatively minor factor. Edit - incidentally, this relates to my suggestion that it is better to measure inductance around 1kHz than at 120Hz (these are the Extech L meter settings). |
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Post by ms on Dec 10, 2016 13:53:34 GMT -5
The imaginary part of the impedance with the effect of the capacitance removed is not a straight line, but rather is below it, increasingly so with increasing frequency. Therefore the effective inductance is less than the low frequency inductance. This is consistent with the apparent "anomaly" in resonant frequencies. I agree that there is not much drop between low frequencies and 1 KHz. Page 7, Least Squares Fit Parameter Results, upper left chart, "L-fit (henries)" vs. frequency. The inductance appears to peak at about 7H somewhere very low (the expanded scale makes it hard to interpret). It looks like it might be about 100 Hz. At 5kHz it has dropped to about 5H. Above that, there isn't much change. I don't have a P90 in particular to test, but assuming a self resonant frequency of about 8k and a loaded resonant frequency of about 3k (typical PAF) , from that chart the only difference would be about (5.2-4.7)H = 0.3H. I see how that would alter the resonant frequency, but I'm not grasping the importance. If the estimate for L at self-resonance is high, the only consequence that I can see, is that the capacitance might be underestimated. But in the application of that data, which normally is understanding how the pickup will perform in circuit, the self capacitance is usually a relatively minor factor. Edit - incidentally, this relates to my suggestion that it is better to measure inductance around 1kHz than at 120Hz (these are the Extech L meter settings). The significance is that eddy currents affect the resonant frequency, not just the losses. This is something that must be understood. One way to approach it is to think of the pickup coil as the primary of a transformer and the cores as a secondary, or at least the currents that circulate near their surface. This transformer is dominated by leakage flux, and so its circuit model has a leakage inductance in series with the secondary load resistor, contributing to the frequency dependent effects. This is why I disagree with your suggestion to not measure at 120 Hz. We must think of this in terms of a circuit model, and the most basic element is the pickup coil. Its inductance is that which is measured at low frequencies. (The apparent variation of the inductance at low frequencies in that plot is a measurement problem.) At 1KHz you can start to see the effects of eddy currents, and thus a measurement at 1KHz says something about the additional elements in the circuit model necessary to reproduce the eddy current effects. |
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Post by stratotarts on Dec 10, 2016 14:01:41 GMT -5
The output of the SH-1n in a typical guitar circuit is -13dB at the self resonance frequency of 7650Hz. Any differences at that frequency are for all intents and purposes, inaudible. So I don't see the importance.
It might be an overly simplistic model, but the effect of eddy current losses in all the experiments I have done, have been on the Q and never the frequency, except by extremely small numbers. I have performed many experiments where the components that produce eddies have been physically removed and readings compared - with almost no change in resonant frequency.
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Post by ms on Dec 10, 2016 14:15:32 GMT -5
The output of the SH-1n typical guitar circuit is -13dB at the self resonance frequency of 7650Hz. Any differences at that frequency are for all intents and purposes, inaudible. So I don't see the importance. It might be an overly simplistic model, but the effect of eddy current losses in all the experiments I have done, have been on the Q and never the frequency, except by extremely small numbers. I have performed many experiments where the components that produce eddies have been removed and compared - with almost no change in resonant frequency. The dominant eddy current loss is from the cores (if steel). Did you really replace the cores with something with the same permeability, but without the conductivity? That is not such an easy thing to do. How accurate is that self resonance measurement? How much capacitance does your set up have? |
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Post by antigua on Dec 10, 2016 14:51:34 GMT -5
I didn't get a chance to read all the above real carefully, as I wanted to hurry up and get this bode plot done. These are unloaded peaks, so they incorporate the pickup's capacitance, and about 10pF in the test equipment. The different slugs are loaded into the same pickup used for the inductance measures, then the popsicle stick coil was used for driving a magnetic field in over the "D" pole piece. The path lines were all normalized to 6 dBV at 1kHz, so demonstrate how the tone might vary with these materials. At first I altered the voltage of the driver to get them close, but they were still rather far apart, so I wrote a script to normalize the data points to 1kHz, and in hind sight I could have done that from the get go, and then I would have absolute as well as normalized plots. If anyone is interested in absolute output voltages for a fixed input voltage, it wouldn't take too long to conduct. I'm willing to redo the test again. |
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Post by stratotarts on Dec 10, 2016 17:52:37 GMT -5
The output of the SH-1n typical guitar circuit is -13dB at the self resonance frequency of 7650Hz. Any differences at that frequency are for all intents and purposes, inaudible. So I don't see the importance. It might be an overly simplistic model, but the effect of eddy current losses in all the experiments I have done, have been on the Q and never the frequency, except by extremely small numbers. I have performed many experiments where the components that produce eddies have been removed and compared - with almost no change in resonant frequency. The dominant eddy current loss is from the cores (if steel). Did you really replace the cores with something with the same permeability, but without the conductivity? That is not such an easy thing to do. How accurate is that self resonance measurement? How much capacitance does your set up have? I didn't replace any poles or cores. I'm referring to brass covers and the copper test loops that I used in my cover study. The input capacitance of the test box is 10 pF and the resistance is 11M. I'm not saying the resonant frequency is not affected by such things, I'm questioning the degree to which they are. Anyway, your approach is extremely interesting because it captures the phase response, therefore the complex impedance Z across the entire range of frequencies. Thus it is a complete black box model. However, attempting to interpret such plots directly seems to me unlikely to be very insightful. It would be better to allow software to transform the values into bode plots that are based on circuit models (either simple, as in the standard 200k/470pF load that we have adopted, or complex as John has done, where control circuit load models can be selected and tested. That is because those are the curves that directly define the tone. Essentially, one could proceed with practical application of the data and muse about the various effects of capacitance and inductance, rather than having to depend on them to obtain practical plots. I will have a good look at your stuff this week. Why not repost all your stuff in a new thread here? I'm sure it's going to generate a lot of focused discussion. Edit for an afterthought - you should test the idea of independence from cable/ADC capacitance by comparing results when adding a cap in parallel with the 1k load resistor. It's fine to theorize that it's okay, but it's a really easy practical test that would put to rest any concerns about that. |
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Post by JohnH on Dec 11, 2016 2:41:22 GMT -5
This is all very interesting stuff. we have had quite a number of discussions I this group about what and how to measure to capture pickup response. I had thought about the impedance measurements before, and they can be done either as real and imaginary parts, or magnitude and phase angle.
But I don't think that they capture a pickup response alone, in the way that the bode plats can do. At each frequency, in addition to two impedance parameters (real + imag, or mag + phase), we also need an output voltage. I think those three values then do capture the response, and can be feed into an analysis or simulation of downstream components.
Mike, my interest in all this is to model pickup response by spreadsheets, to build the resulting pickup models into larger models that include other electrical and non electrical aspects (see GuitarFreak ).
Inside the spreadsheet, I use exactly the kind of impedance data that you measured directly. But I've been deriving this data from curve fitting a 6 part model of fixed components to match the sets of bode pots from Antigua and stratotarts. In my mind, the reason for having to discuss how things like Inductance changes with frequency is because the truth is more complex than can be captured with just a single fixed value. My method, which is a couple of steps better but is still always an approximation, uses two fixed inductances plus resistors and cap to lock onto the main response characteristics. I have not yet found any of the response tests that have been posted here that can not be captured quite well across a range of frequencies and loading conditions, including pickups with significant eddy effects. I agree eddy effects are often best thought of as being derived from poorly coupled 'transformers'. My models imply that the effects of these transformers can be reflected back into the primary, which I understand is a recognised approach in transformer theory (at this point, im beyond the theory that I can remember)
J |
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Post by ms on Dec 11, 2016 7:01:09 GMT -5
Edit for an afterthought - you should test the idea of independence from cable/ADC capacitance by comparing results when adding a cap in parallel with the 1k load resistor. It's fine to theorize that it's okay, but it's a really easy practical test that would put to rest any concerns about that. My apogee Duet died and I bought a temporary replacement for a bit over $100, a Tascom US 2x2. The cheap pots make adjustments difficult, and trying to get the channel gains the same is really hard. Also there appears to be something funny about the digitation approaching 20 KHz. I use the preamp in both channels because flaws tend to be greatly reduced when the technique involves taking a ratio as long as the two channels are very similar. The test I use to convince myself that the high frequency impedance measurements are OK is to measure the impedance of a 330K resistor. In addition to the real part, you get a small imaginary part that ramps up from zero. Some of this is associated with the resistor itself, some with the measuring device. At 20 KHz, this imaginary part affects the magnitude of the impedance by less than 1% (the real part is a bit noisier than it should be, however), and the phase is a bit less than four degrees. This might sound impossibly good, but it is the result of the correcting power of a ratio in the measurement process. Errors in the frequency response that are the same in the two channels are divided out (unless so severe that they destroy the SNR). Thus the effect the capacitance of the one foot mass produced cables that I use is nearly all gone, and so on. |
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Post by ms on Dec 11, 2016 7:24:11 GMT -5
This is all very interesting stuff. we have had quite a number of discussions I this group about what and how to measure to capture pickup response. I had thought about the impedance measurements before, and they can be done either as real and imaginary parts, or magnitude and phase angle.
But I don't think that they capture a pickup response alone, in the way that the bode plats can do. At each frequency, in addition to two impedance parameters (real + imag, or mag + phase), we also need an output voltage. I think those three values then do capture the response, and can be feed into an analysis or simulation of downstream components.
Mike, my interest in all this is to model pickup response by spreadsheets, to build the resulting pickup models into larger models that include other electrical and non electrical aspects (see GuitarFreak ).
Inside the spreadsheet, I use exactly the kind of impedance data that you measured directly. But I've been deriving this data from curve fitting a 6 part model of fixed components to match the sets of bode pots from Antigua and stratotarts. In my mind, the reason for having to discuss how things like Inductance changes with frequency is because the truth is more complex than can be captured with just a single fixed value. My method, which is a couple of steps better but is still always an approximation, uses two fixed inductances plus resistors and cap to lock onto the main response characteristics. I have not yet found any of the response tests that have been posted here that can not be captured quite well across a range of frequencies and loading conditions, including pickups with significant eddy effects. I agree eddy effects are often best thought of as being derived from poorly coupled 'transformers'. My models imply that the effects of these transformers can be reflected back into the primary, which I understand is a recognised approach in transformer theory (at this point, im beyond the theory that I can remember)
J I agree that a model with a few theoretically perfect components (that is, no frequency dependence in these components) is the way to go. It is an interesting question, what you need besides impedance measurements. I like to think of pickup response as composed of two parts, the law of induction part, and the circuit part. The impedance measurement is aimed at the circuit part. The other part consists of at least the 6 db/octave increase, but is there more? I think the answer to this is part of the eddy current issue. The response to eddy currents can be divided into two parts. First, is the effect on the impedance. Measurements seem to show that this is the dominant one. But there is another part. If the vibrating string excites a current in, for example, a cover, then this current causes a changing magnetic flux through the pickup coil that subtracts from the effect of the string. This effect is at least partly accounted for in an impedance measurement since such a measurement also excites current in the cover, but I doubt that it is the full effect. Thus I think that there is a small effect that the impedance measurement does not capture, but I do not really know. This seems like a good thing to investigate from both theory and measurement directions. |
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Post by antigua on Dec 11, 2016 9:00:34 GMT -5
We've only talked about eddy currents in the cores, does anyone know if hysterisis losses are at work here also? Would hysterisis losses be higher for alnico poles than steel?
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Post by ms on Dec 11, 2016 9:53:34 GMT -5
We've only talked about eddy currents in the cores, does anyone know if hysterisis losses are at work here also? Would hysterisis losses be higher for alnico poles than steel? Histerisis is not an issue because the currents are too small to move the medium along the curve |
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Post by antigua on Dec 11, 2016 16:43:28 GMT -5
We've only talked about eddy currents in the cores, does anyone know if hysterisis losses are at work here also? Would hysterisis losses be higher for alnico poles than steel? Histerisis is not an issue because the currents are too small to move the medium along the curve Thanks, so you would say that the pickup generates a very tiny H field? |
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Post by stratotarts on Dec 11, 2016 19:00:50 GMT -5
Histerisis is not an issue because the currents are too small to move the medium along the curve Thanks, so you would say that the pickup generates a very tiny H field? The string generates a very tiny H field. |
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Post by reTrEaD on Dec 19, 2016 11:23:20 GMT -5
Steel is a lot more permeable than any of the AlNiCos. Bear with me. Just some noob musings to follow . . . I get the impression that steel is the real culprit in ceramic pickups. I have to wonder if ceramic magnets in the same shape as the AlNiCo slugs might not be so offensive in terms of shifting the resonant peak to a lower frequency. I would imagine it's much easier to machine steel into a slug and slap a magnet or two on the backside of the flatwork. But it doesn't seem as if it would be all that difficult to bake ceramic magnets in the same shape as the slugs. Yet we don't see that. Any thoughts on this? |
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Post by stratotarts on Dec 19, 2016 12:04:11 GMT -5
Steel is a lot more permeable than any of the AlNiCos. Bear with me. Just some noob musings to follow . . . I get the impression that steel is the real culprit in ceramic pickups. I have to wonder if ceramic magnets in the same shape as the AlNiCo slugs might not be so offensive in terms of shifting the resonant peak to a lower frequency. I would imagine it's much easier to machine steel into a slug and slap a magnet or two on the backside of the flatwork. But it doesn't seem as if it would be all that difficult to bake ceramic magnets in the same shape as the slugs. Yet we don't see that. Any thoughts on this? Sure. In the case of humbuckers, there are many reasons. I believe the main reason for using steel is to reduce the number of magnets to only one. That reduces material and assembly cost. Ferrite and Ceramic magnet material is brittle, it can't readily be made into screws. The number of players that actually adjust the filister screws is miniscule, yet there they are. It's my impression that the reason they are used instead of slugs is mainly historical and aesthetic. IIRC, Seth Lover's prototype PAF had no screws, and they were added to make it look more like a P-90. In the case of the Fidelitron, they help to secure the coils. It would be possible to either use magnets directly, as with Firebirds or Strat/Tele, or to replace steel with Ferrite, which has high permeability, while retaining the single under-slung magnet. Ferrite pole pieces would definitely be feasible, but are not currently available in the correct dimensions. A pickup made with those would have to have them in both coils, which would lead to a flat, shiny, screwless top. That would be a hard sell to consumers who don't have any understanding of poles, and may not even realize that there are a second, hidden set of poles under the cover. Any such pickup would appeal to a smaller market, since many players have become accustomed to the tonal response of the steel based designs, and would have to follow a learning curve in order to benefit from the extended range of an improved design, while still being able to reproduce the tones that they already have. |
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Post by ms on Dec 19, 2016 12:27:41 GMT -5
Bear with me. Just some noob musings to follow . . . I get the impression that steel is the real culprit in ceramic pickups. I have to wonder if ceramic magnets in the same shape as the AlNiCo slugs might not be so offensive in terms of shifting the resonant peak to a lower frequency. I would imagine it's much easier to machine steel into a slug and slap a magnet or two on the backside of the flatwork. But it doesn't seem as if it would be all that difficult to bake ceramic magnets in the same shape as the slugs. Yet we don't see that. Any thoughts on this? Sure. In the case of humbuckers, there are many reasons. I believe the main reason for using steel is to reduce the number of magnets to only one. That reduces material and assembly cost. Ferrite and Ceramic magnet material is brittle, it can't readily be made into screws. The number of players that actually adjust the filister screws is miniscule, yet there they are. It's my impression that the reason they are used instead of slugs is mainly historical and aesthetic. IIRC, Seth Lover's prototype PAF had no screws, and they were added to make it look more like a P-90. In the case of the Fidelitron, they help to secure the coils. It would be possible to either use magnets directly, as with Firebirds or Strat/Tele, or to replace steel with Ferrite, which has high permeability, while retaining the single under-slung magnet. Ferrite pole pieces would definitely be feasible, but are not currently available in the correct dimensions. A pickup made with those would have to have them in both coils, which would lead to a flat, shiny, screwless top. That would be a hard sell to consumers who don't have any understanding of poles, and may not even realize that there are a second, hidden set of poles under the cover. Any such pickup would appeal to a smaller market, since many players have become accustomed to the tonal response of the steel based designs, and would have to follow a learning curve in order to benefit from the extended range of an improved design, while still being able to reproduce the tones that they already have. So called Ferrite beads with very close the pole piece dimensions are available from places such as Amidon. You have to look around and see who has the right sizes at the moment. The small hole down the middle does not matter. I have made both singe coil and humbucker pickups using them. They are lower loss than alnico, and there are several different permeabilities available, with different losses. Remember, effective permeability never gets high with short open poles. |
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Post by antigua on Dec 19, 2016 13:35:47 GMT -5
Steel is a lot more permeable than any of the AlNiCos. Bear with me. Just some noob musings to follow . . . I get the impression that steel is the real culprit in ceramic pickups. I have to wonder if ceramic magnets in the same shape as the AlNiCo slugs might not be so offensive in terms of shifting the resonant peak to a lower frequency. I would imagine it's much easier to machine steel into a slug and slap a magnet or two on the backside of the flatwork. But it doesn't seem as if it would be all that difficult to bake ceramic magnets in the same shape as the slugs. Yet we don't see that. Any thoughts on this? In this thread I compared the properties of AlNiCo's and steel poles guitarnuts2.proboards.com/thread/7830/electrical-effects-piece-metal-types , and the short answer is yes, it's all the steel's fault. Since the ceramic is not even a metal, it's not conductive or permeable, not to any significant extent, if at all. They have to use steel in order to deliver the flux alignment of the ceramic magnet to the strings on the opposite side of the pickup. The steel pole pieces have the pro of increasing the inductance without also necessarily increasing the parasitic capacitance, but the con of causing eddy currents that take away from the high end, and the con of not delivering as much flux to the strings as AlNiCo pole pieces do. Pickup makers could try using laminated steel cores, and maybe some have. Based on stratotart's findings with eddy current patterns in a guitar pickup, I believe a single radial cut down one side of a steel pole piece or screw would get rid of most of the eddy currents, since they spin with the circumference of the cylinders. As said above, it would be hard to make ceramic screws and such, but they could use rubberized ferrite, as is done with Lace Sensors, in order to make unusual shapes. Since the ferrite would have less permeability than either steel or AlNiCo , you would need more turns of wire to get the same inductance, which would mean higher capacitance, but I think all in all it would work fine, just as a Lace Sensor works fine. There are a lot of possibilities, but guitarists are on a vintage binge at the moment. Maybe the 80's will come back around and guitarists will become daring again. I've been urging any pickup maker who will listen to consider hiding innovative ideas under a vintage correct appearance, especially Lace. They seem prideful in the futuristic look of their products, but it surely hurts their sales in the current "vintage correct" climate. |
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Post by ms on Dec 19, 2016 14:16:43 GMT -5
Bear with me. Just some noob musings to follow . . . I get the impression that steel is the real culprit in ceramic pickups. I have to wonder if ceramic magnets in the same shape as the AlNiCo slugs might not be so offensive in terms of shifting the resonant peak to a lower frequency. I would imagine it's much easier to machine steel into a slug and slap a magnet or two on the backside of the flatwork. But it doesn't seem as if it would be all that difficult to bake ceramic magnets in the same shape as the slugs. Yet we don't see that. Any thoughts on this? Sure. In the case of humbuckers, there are many reasons. I believe the main reason for using steel is to reduce the number of magnets to only one. That reduces material and assembly cost. Ferrite and Ceramic magnet material is brittle, it can't readily be made into screws. The number of players that actually adjust the filister screws is miniscule, yet there they are. It's my impression that the reason they are used instead of slugs is mainly historical and aesthetic. IIRC, Seth Lover's prototype PAF had no screws, and they were added to make it look more like a P-90. In the case of the Fidelitron, they help to secure the coils. It would be possible to either use magnets directly, as with Firebirds or Strat/Tele, or to replace steel with Ferrite, which has high permeability, while retaining the single under-slung magnet. Ferrite pole pieces would definitely be feasible, but are not currently available in the correct dimensions. A pickup made with those would have to have them in both coils, which would lead to a flat, shiny, screwless top. That would be a hard sell to consumers who don't have any understanding of poles, and may not even realize that there are a second, hidden set of poles under the cover. Any such pickup would appeal to a smaller market, since many players have become accustomed to the tonal response of the steel based designs, and would have to follow a learning curve in order to benefit from the extended range of an improved design, while still being able to reproduce the tones that they already have. You can find so called ferrite beads very close in size to a standard pole piece. They have a small hole down the length, but that does not matter. |
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Post by ms on Dec 19, 2016 14:24:51 GMT -5
Since the ceramic is not even a metal, it's not conductive or permeable, not to any significant extent, if at all. They have to use steel in order to deliver the flux alignment of the ceramic magnet to the strings on the opposite side of the pickup. They are a very special ceramic, a so-called ferrite. Although it is true that ceramic (ferrite) permanent magnets tend to have low permeability, the soft magnetic versions can have very high permeability. They also can be very lossy at higher frequencies (used to suppress rf pickup) or not. In the audio range ferrites in general are quite low loss, and permeabilities can be as high as several thousand. |
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Post by antigua on Dec 19, 2016 14:25:34 GMT -5
Yeah, I don't think the bead hole would matter much. Since the coil is around the magnet, the perimeter of the flux is the most important, from the perspective of the coil.
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Post by reTrEaD on Dec 20, 2016 9:17:16 GMT -5
Sure. In the case of humbuckers, there are many reasons. I believe the main reason for using steel is to reduce the number of magnets to only one. That reduces material and assembly cost I agree with the cost factor but I don't think it's quite as simple as reducing the number of magnets. I reckon it has more to do with the fact that steel is cheap, AlNiCo not-so-much. Probably easier on the machining as well. In the case of a strat pickup, the AlNiCo slugs are magnetized so there are actually fewer parts. But steel is cheap and ceramic bars are also cheap to produce. I was thinking strat pickups when I posted that question but looking at it from a HB viewpoint has some interesting twists. I'm enjoying reading your take on this. Ferrite and Ceramic magnet material is brittle, it can't readily be made into screws. The number of players that actually adjust the filister screws is miniscule, yet there they are. It's my impression that the reason they are used instead of slugs is mainly historical and aesthetic. IIRC, Seth Lover's prototype PAF had no screws, and they were added to make it look more like a P-90. In the case of the Fidelitron, they help to secure the coils. It would be possible to either use magnets directly, as with Firebirds or Strat/Tele, or to replace steel with Ferrite, which has high permeability, while retaining the single under-slung magnet. Ferrite pole pieces would definitely be feasible, but are not currently available in the correct dimensions. A pickup made with those would have to have them in both coils, which would lead to a flat, shiny, screwless top. That would be a hard sell to consumers who don't have any understanding of poles, and may not even realize that there are a second, hidden set of poles under the cover. I vaguely recall some HBs (in the 70s maybe?) that had a plain flat cover. iirc, I didn't care for the sound. I doubt that was due to the lack of screws. More likely because they were overwound. Any such pickup would appeal to a smaller market, since many players have become accustomed to the tonal response of the steel based designs, and would have to follow a learning curve in order to benefit from the extended range of an improved design, while still being able to reproduce the tones that they already have. From my point of view, any way to extend the frequency response is inherently good. We can take steps to tame down peaks through loading if necessary. Maybe I'm looking at this wrong? idk. |
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