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Post by ms on Nov 20, 2023 6:19:28 GMT -5
Towards the end of of Tillman, "Response Effects of Guitar Pickup Position and Width": "Pickups do not sense the string at a single point source, but rather over an area due to the width of the magnetic field. This sensing area is called the "aperture" of the pickup and is about an inch wide on a thin single coil pickup and about 2.5 inches wide on a wider pickup such as the Gibson humbucker."
I wouldn't refer to this unless he fixes it. This is a popular article, and so responsible for much misunderstanding.
McD's article is a great introduction to how the law of magnetic induction works, but it is very much intended to be viewed with "physics thinking", that is, something made fun of by the old joke about assuming a spherical cow. His assumptions about the magnetic field from the string are not in line with reality, and he does not make this clear.
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Post by ms on Nov 18, 2023 6:15:08 GMT -5
From the article you referenced: 'Using a “shunt" resistor works well to reduce highs and offers an excellent alternative to replacing the pickup itself.' When you replace a pickup, you usually change the resonant frequency of the circuit by changing the inductance of the pickup. The shunt resistor makes the resonance lower and broader, a different thing, but actually, you need to be able to do both. It is possible to lower the resonant frequency without changing the pickup as well. You can put inductance in series. So I think you can do what I think you want, that is, lower the resonant frequency and lower the Q (broader and lower peak) of just the one pickup. I have never heard of anyone doing both these steps together, but it should work. OK. that's one approach. The idea situation is just to reduce some shrill at "10" on the pot and leave the other points alone (in terms of how the tone pot sees them), I think that is what gckelloch is going for. But he points out there is some 'collateral damage' (reduced volume) with putting a resistor in parallel, so this may be a non-starter, as he likes the pickup at all the other points on the tone sweep I finally found the other link I was searching for about using capacitors to kill shrill, this seems to have a global effect so would move the resonant peak for any point 10-1 as seen by the tone pot....so won't not meet his criteria either (my interpretation of what I think he has going on in his bridge pickup). Here is the link and toward the end he shows mounting. Yes, interesting, but maybe more so on a pickup which is really misbehaving tonally than one that is 'close to perfect'.... Try this before buying new pickups Too much collocal change I think , so the question is if there is a more surgical way to tweak (maybe). I'm guessing no.... When you add a small value capacitor in parallel with the pickup, its effect is mostly washed out with a low number tone setting because the value of the tone capacitor is significantly larger, and so the value of the two in parallel has not relatively changed that much. Adding inductance in series does affect the lower frequency resonance from the tone capacitor at low number tone settings. When you change the pickup, you are mostly changing the inductance. So maybe if you want to do something similar to changing the pickup, adding inductance in series would be the closest thing. My experience is that you need the two degrees of freedom, location of peak and width of peak, but you do have some options as to how to do this, but they are not all exactly the same.
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Post by ms on Nov 17, 2023 19:51:26 GMT -5
Well nothing is perfect, tastes and opinions change. etc. I think you are far ahead of the curve on this in terms of getting ideal sounds. There are some ways to throw an extra cap or resistor in parallel to pull out the shrill at "10" without really affecting anything else, and some of the other forum members will know this far better than me and should chime in, as this is something I'd like to know better both theoretically and practically. Here is one article on 'taming' the shrill and keeping it just on one pickup. Shrill killing They show one to 3 locations, but honestly it can be even be located on the 5-way itself (I can't find that video today, but I've seen it before, sigh) Thanks for the 'Wilde' construction info! Lots of good pickup design approaches out there. From the article you referenced: 'Using a “shunt" resistor works well to reduce highs and offers an excellent alternative to replacing the pickup itself.' When you replace a pickup, you usually change the resonant frequency of the circuit by changing the inductance of the pickup. The shunt resistor makes the resonance lower and broader, a different thing, but actually, you need to be able to do both. It is possible to lower the resonant frequency without changing the pickup as well. You can put inductance in series. So I think you can do what I think you want, that is, lower the resonant frequency and lower the Q (broader and lower peak) of just the one pickup. I have never heard of anyone doing both these steps together, but it should work.
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Post by ms on Sept 24, 2023 10:12:32 GMT -5
I didn’t know that. I believed the magnet could be anywhere as long as the string is sufficiently magnetized near the coil. That's true, but the type of alloy in the core of the coil affects the inductance. An ac magnetic field generated by current in one loop of the coil generates a voltage around other loops of the coil. A permeable pole piece increases this voltage, and so increases the inductance. Also, it increases the voltage generated by a hum magnetic field.
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Post by ms on Sept 23, 2023 18:32:58 GMT -5
Thanks for your answer. I don’t understand the hum cancellation part of you answer. The two coils are still connected in series, why would the cancellation stop ? I don’t remember hearing any hum since I removed them. Because the cores increase the sensitivity to magnetic fields. If you remove them from one coil, then you have made one coil less sensitive to hum than the other.
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Post by ms on Sept 23, 2023 10:10:11 GMT -5
Pickup pole pieces are short and part of an open magnetic circuit. That is, the magnetic circuit is mostly air gap. This means that changing the permeability of the pole pieces only has a small effect when the permeability is large. So changing from a carbon steel with a permeability of 100 to one with 200 would not make a lot of difference. In both cases, the coil inductance would be about three times that with air pole pieces. So when you took the pole pieces out of one of the coils of a humbucker, you lowered the inductance a noticeable amount, but also ruined the hum cancelation. (If you are in a "hummy" environment, you can hear it increase as you remove each pole piece.)
Edit: That figure is BS for large mu (even though it is from a "reputable" site). The equation would be almost correct for large mu if the core is closed, such as a toroid or the more usual closed transformer core type. With the core shown, it would be OK for mu = 2 or 3, maybe.
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Post by ms on Sept 21, 2023 9:47:15 GMT -5
There seems to be some agreement that a Franz is underwound compared to a P-90 and therefore is brighter and thinner. (https://letstalkguild.com/ltg/index.php?threads/silly-question-why-franz-pickups.149404/) So here is something that probably won't solve all your problems, but is easy to do: Use a really high capacitance cable. You can hook multiple cables together, or maybe one of those awful coilly things would do. I suspect that you would need to alter the resistance across the circuit, too, but the simplest change might give give you an idea if you are heading in the right direction. Remember: pickups are not magic; they are electronic circuits, and there often is more than one way to achieve an effect.
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Post by ms on Sept 21, 2023 6:03:15 GMT -5
Yes I was a tad surprised with the (low) 8-bit spec of the Velleman and the Picoscope 2204A when I saw it. On the other hand it's often much easier to optimize the volts/bit with gain (range) settings in a digital oscilloscope than it is with most ADC boards I've worked with (which instead tend to have 12 or 16 bit sampling). The "enhanced" resolution with the 2204A does gain a few extra bits by over-sampling ....
My experience with interfacing to hardware is mostly with (expensive) Matlab. Not sure if (free) Octave can use the same drivers/APIs ?
I think Octave uses the same drivers, but I do not know. (I use Python, which I realize is not the choice most people make.) Picoscope: "For this technique to work, the signal must contain a very small amount of Gaussian noise, but for practical applications this is generally provided by the scope itself and the noise inherent in normal signals." This reads like something out of the 1980s. You get 24 bits at 192 KHz in a current recording interface. Sure, the lowest order bits are not perfect, but that is not important when you have so many.
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Post by ms on Sept 20, 2023 6:29:53 GMT -5
If you think you need to move to a device that does not do the data analysis for you, one thing to consider is moving to a different type of hardware. Relative to the requirements of pickup analysis, the USB digital scope has too few bits in the quantization, but samples a lot faster than necessary. It is OK with the integrator circuit, and it is convenient if it does the analysis (plotting, etc.) for you with an integrated software package. It that is no longer available, then you could change to a device with a lots more bits. Recording interfaces typically sample up to 192 KHz, plenty fast enough, and have really good digitizers. You need a software package for data taking; I think most people would prefer Octavia (the free Matlab replacement).
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Post by ms on Sept 19, 2023 18:55:00 GMT -5
If you load a pickup with the actual circuit, there is no need to study it much past a few KHz. Guitar speakers fall really fast above 5 KHz (some even lower), and simulation software should too to reproduce the actual situation. On the other hand, if you want to understand the complete pickup circuit, measure it unloaded to as high a frequency as necessary to include all detail. I already have the unloaded measurement plots. Though I suppose going further to see if the peak shows up unloaded might be interesting. After that I'll get the real loaded plots. I'm doing this for the sake of measuring and having the data available more than anything else. You know, I don't recall seeing separate magnets like a P90, but that doesn't mean they weren't there. If I remember to look, I'll check next time I have the guitar. There might be no peak. If the poles pieces are sufficiently conductive, the eddy currents induced in them might be sufficient to damp out a peak, if this possible peak is high enough in frequency.
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Post by ms on Sept 19, 2023 7:34:54 GMT -5
By the way, are those pole pieces made of steel or permanent magnetic material? My best guess is that they are steel, and there is are alnico magnets underneath as in a P-90 with the steel pole pieces replacing the P-90 screws.
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Post by ms on Sept 19, 2023 6:29:18 GMT -5
Put the pickup faces together. If they attract, they are RWRP. If they repel, they're not RWRP. Because, for RWRP, the magnet polarity must be opposite. They're definitely RP, but that's not a reliable test for RW. The guy that put these pickups in the guitar was...odd. He flipped one of the mounting plates, and reversed all the pole screws to do some dumb stuff. I'll just assume they are RWRP, but the guy could have easily reversed the magnets in the process of his shenanigans. But when wired together with the wires connected as intended do they reduce hum? I guess you can always make them do so if you want since you can reverse the magnets, if necessary, and reverse the leads if required.
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Post by ms on Sept 19, 2023 6:24:47 GMT -5
If you load a pickup with the actual circuit, there is no need to study it much past a few KHz. Guitar speakers fall really fast above 5 KHz (some even lower), and simulation software should too to reproduce the actual situation. On the other hand, if you want to understand the complete pickup circuit, measure it unloaded to as high a frequency as necessary to include all detail.
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Post by ms on Sept 18, 2023 6:22:47 GMT -5
It's exactly what you would expect from P90's. I'm curious, were they RWRP? I don't know how to check if one is reverse wound, but I would assume yes as the pickup lead colors are reverse polarity on one of them. Is there a magic trick to check the wind direction that doesn't require removing the pickup tape? If you have both pickups on the bench, you can try connecting them together with both polarities and see if one way has more hum than the other, using you favorite measuring device or even an amp.
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Post by ms on Aug 29, 2023 6:42:19 GMT -5
When we plot the frequency response of some system, it seems to me that it is helpful for resonances of different frequencies to have the same shape if they have the same Q. Since Q is related to center frequency over frequency width, a log scale meets the condition.
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Post by ms on Aug 8, 2023 6:06:59 GMT -5
"it took us 20 years to learn how to use that thing. now we live by it."
20 years? Utter nonsense or incredible stupidity!
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Post by ms on Aug 3, 2023 14:23:08 GMT -5
From my basic understanding of the inherent hum cancelling properties of the humbucker magnet configuration, it would appear that wiring the two coils in parallel, start to start, and finish to finish, as shown in the circuit diagrams, should preserve the hum cancelling properties - i.e. the inherent magnetically coupled common mode rejection of the humbucker configuration. So the coils are wound in opposite directions?
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Post by ms on Jul 30, 2023 13:06:04 GMT -5
They have to go in series to have the correct inductance. If you put them parallel, the total inductance goes down to less than what it should be and the resonance frequency rises up higher than you want it. If the resonant frequency is too low with them in series, then you need to use maybe 25% fewer turns on each coil. Thanks for the answer! Yes, you are right! It is in serial connection that everything sounds as it should. Maybe there is a problem of parallel connection with loss of resonance, adding turns of the coils, will it be possible to compensate? Two identical (non-coupled) inductors in parallel have half the inductance of one of them. You might try adding turns, but what is wrong with a series connection?
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Post by ms on Jul 30, 2023 10:24:28 GMT -5
In addition to everything described, I noticed that when two pickups with split coils are turned on in parallel, the signal loses a lot of useful timbre and the middle frequencies are weakened. I got this result when I wound 2 split singles for my jazz bass, and each sounds good individually, but in a pair - not the result I wanted. Who can express an opinion on this matter, why is this happening? Thank you! They have to go in series to have the correct inductance. If you put them parallel, the total inductance goes down to less than what it should be and the resonance frequency rises up higher than you want it. If the resonant frequency is too low with them in series, then you need to use maybe 25% fewer turns on each coil.
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Post by ms on Jul 28, 2023 14:30:52 GMT -5
IMO, the two most important numbers are the location of the resonant peak in the frequency response and the Q of this resonance. I do not think that the Q is important far from the peak, but maybe this needs to be explored.
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Post by ms on Jul 25, 2023 6:45:55 GMT -5
*** In my post above, I should have said that the series R increases with increase in eddy current losses.
From the data above (and other measurements I am familiar with) single coil alnico core pickups have the highest Qs (leaving out ferrite cores from the discussion) in the few KHz range. But they also have higher C than humbuckers because humbuckers use two coils in series, lowering the C. Steel is more conductive than alnico; I think we have good evidence then that it is the eddy currents that dominate the Q in the important range around, say, 3 KHz, not the effect of the coil C. The effect of the C is still there, of course, and it should dominate as frequency increases since its effect increases faster than the effect of eddy current losses.
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Post by ms on Jul 24, 2023 20:01:42 GMT -5
you expect the Q of an inductor to rise with frequency: Q = 2*pi*f*L/R. For a pickup with metal cores you expect it to drop with further increases as the losses increase (that is, series R drops), resulting from eddy currents.
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Post by ms on Jul 21, 2023 19:20:25 GMT -5
one dead giveaway that a guitar has active pickups (besides the presence of a 9v battery snap) is that the pot values are much lower than what we'd normally use. passive pickup-equipped strat usually uses 250k pots where one with active pickups will use 25k or 50k pots. this is because the active pickups present a low impedance signal so 'normal' value pots only really act as an on/off switch. in order to have the tone control act on the same frequencies the tone cap is embiggened, so instead of 22nf a 220nf cap might be used (rc filters are fun). if you're interested in the math we can nerd out further but that can take away from the geetar playing cool find, by the way! The purpose of a lower value volume control is to drive the cable capacitance better so that the frequency response of the instrument is almost independent of the volume setting. Or, looking at it the other way, the reason for making the output impedance low is to make it possible to use a lower value volume control, enabling better uniformity of frequency response with control changes. With a passive pickup, the tone control damps the Q of the resonant circuit formed by the coil inductance and cable and coil capacitance, and also introduces a much lower resonant frequency as the tone control approaches zero. The output of the preamp does not have this property, and so the tone control behaves differently.
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Post by ms on Jul 8, 2023 17:50:52 GMT -5
An LCR metter at 100 KHz can do a pretty good job. For example, a Filter'tron I had sitting on the table measures 186 pf, kind of high for a pickup with two coils in series, but this does include the capacitance of the shielded lead made from very thin cable, probably high C. I prefer to measure the impedance over a wide range of closely spaced frequencies and use some math to get a capacitance value at a frequency much lower than 100KHz.
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Post by ms on Jun 22, 2023 6:01:21 GMT -5
I remember that plot. Unusual screws, yes. I do not understand how this works.
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Post by ms on Jun 21, 2023 14:40:38 GMT -5
I would say that pretty well every pickup response can be considered as made up of two cascaded filter responses. There is a 2nd order low pass with some sort of a peak and also a more or less first order low pass shelf. The low pass shelf is caused by the eddy current losses and is essentially unaffected by loading. The 2nd order low pass is very much affected by loading. If the low pass shelf starts well before the 2nd order part starts a steep rise to the peak, the pickup will show the scoop in the response.
That's a little abstract for me, but do you have any theory why the Filter'tron shows the effect so dramatically compared to the PAF type? They have the same overall layout, but the proportions of the parts are a lot different. IIRC, the filister screws are mostly what is responsible for the scoop, but it's not clear why the effect is much different as compared with APF screws and slugs. Are you sure it is the fillister screws? It makes more sense to me that the "scoop" (not part of the resonance) is caused by metal outside of the coil itself, such as a cover that can block signal at higher frequencies. I played around with a Filter'tron recently, and thought that it was the thick brass cover that did it. (Perhaps you made some measurements on a Filter'tron a while ago, but I did not find the discussion in order to review your results.)
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Post by ms on Jun 20, 2023 5:56:59 GMT -5
The dip before resonance seems to be greatest in pickups with a lot of metal, such as a thick brass cover. More eddy currents, I suppose.
Edit: Maybe loading broadens the peak, tending to cancel out the dip.
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Post by ms on Jun 16, 2023 5:46:42 GMT -5
"Electric Field Interference", "Magnetic Field Interference": Excellent, I will try to use these descriptions.
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Post by ms on Jun 12, 2023 6:54:54 GMT -5
I believe that you can compute the measured impedance from the measured values as part of the more refined analysis.
If you want the meter to compute L, R, and C, it needs to measure at two or more frequencies. It would be simplest to measure at a high frequency to get C, but there are potential complications with pickup coils wound in strange patterns.
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Post by ms on Jun 12, 2023 6:07:02 GMT -5
Dictionary Definitions from Oxford Languages e·lec·tro·stat·ic adjectivePHYSICS adjective: electrostatic relating to stationary electric charges or fields as opposed to electric currents.
When you limit "electrostatic" to charge in very good insulators and created by frictional or similar means, you are forced to use the term "electromagnetic" to describe the result of a motionless or near motionless charge distribution that can create no or no significant magnetic field. That seems more confusing.
Dictionary Definitions from Oxford Languages e·lec·tro·mag·net·ic adjective relating to the interrelation of electric currents or fields and magnetic fields. Feedback
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