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Post by straylight on Jun 28, 2018 11:08:26 GMT -5
Going through my test rig for sources of error had me thinking about my pickups and how i'm scatter winding with the aim of reducing capacitance and not always achieving goals, paying particular attention to my wiring. Pains me to admit it but the pushback cloth brigade might have been right to some extent. I'm looking at 340pf/M for the single core and shield wire I've been buying by the reel for the last decade and 250pf/M for the 4 core + shield wire I have in smaller quantities, which seems to be similar to the scavenged USB cables I have kicking around. 0.6mm dia single strand wire is about 68pF/m for a twisted pair, varying a little with twist, I may have replicated cat 5 twist rates out of habit. Much better but I don't like using single strand for pickups as it's prone to handling breakages. I can easily compensate for cable length in single coil pickup testing and I just put a meter of cable on a pickup and cut it down 10cm at a time to satisfy myself that I'm right. 4 conductor wire is more complicated. The capacitance in wires for the split seems to be irreleveant or otherwise swamped, I suppose I should spice model this and see what it does? Anyone have an insight?
Anyone have capacitance values for pushback cloth wire vs a similar gauge of pvc?
I note my lone dimarzio single coil has two untwisted PVC insulated cables in a guitar sporting two 4core+shield humbuckers from factory.
I further note that the only guitar I owned that I never felt the need to modify beyond fixing a scratchy pot was a early Maverick X1 that had a twisted pair of wires from each of the two coil over alnico rod humbuckers. I don't know if it was standard, but i understand it to have been a demonstrator at the first UK Maverick dealer and then owned by the son of one of the store owners, so he probably had easy access to quite talented but awkward to engage store luther.
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Post by stratotarts on Jun 29, 2018 10:15:58 GMT -5
Anyone have capacitance values for pushback cloth wire vs a similar gauge of pvc? The permittivity of PVC is likely much higher than cloth. For one thing, cloth has a porous structure that contains a lot of air. Thus cloth dielectric generally makes lower capacitance than PVC. But for single conductor, capacitance is not a measureable or meaningful value. If you have a pair of conductors with a known diameter and spacing, and a uniform dielectric material between, you can begin to calculate or specify capacitance. Further, the greater the wire spacing, the less effect the insulation will have on the capacitance. If you run wires loosely in a control cavity, or twist them manually, the values will be different every time. |
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Post by straylight on Jun 29, 2018 12:22:22 GMT -5
Perhaps I could have phrased that better, but I was wary of being too specifc.
1 pair wires, separated 20mm each end, 1m long under 1N tension. I supose then we end up needing to simulate a shileded and unshileded guitar. It's going to be fairly small I asume though, handful of pf. Time to hit up the internet for wire then...
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Post by stratotarts on Jun 29, 2018 14:09:09 GMT -5
Perhaps I could have phrased that better, but I was wary of being too specifc.
1 pair wires, separated 20mm each end, 1m long under 1N tension. I supose then we end up needing to simulate a shileded and unshileded guitar. It's going to be fairly small I asume though, handful of pf. Time to hit up the internet for wire then...
Sure, you can set up a measurement like this. It would be better to reduce the distance from 20mm to as small as you can get away with, to increase the effect of the dielectric to the point where you could actually measure it. I found a value online for PVC, it's listed as 3.19. Compares well with paper, 3.85. Unless you are considering using 1cm thick insulation, most of the space between the conductors will be air, which has a relative permittivity of almost 1. That will dominate the equation. It's when the conductors get close to each other relative to their area (such as in coax), that the capacitance and the influence of the dielectric really takes off. |
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Post by antigua on Jun 30, 2018 13:47:56 GMT -5
Going through my test rig for sources of error had me thinking about my pickups and how i'm scatter winding with the aim of reducing capacitance and not always achieving goals, paying particular attention to my wiring. Pains me to admit it but the pushback cloth brigade might have been right to some extent. I'm looking at 340pf/M for the single core and shield wire I've been buying by the reel for the last decade and 250pf/M for the 4 core + shield wire I have in smaller quantities, which seems to be similar to the scavenged USB cables I have kicking around. 0.6mm dia single strand wire is about 68pF/m for a twisted pair, varying a little with twist, I may have replicated cat 5 twist rates out of habit. Much better but I don't like using single strand for pickups as it's prone to handling breakages. I can easily compensate for cable length in single coil pickup testing and I just put a meter of cable on a pickup and cut it down 10cm at a time to satisfy myself that I'm right. 4 conductor wire is more complicated. The capacitance in wires for the split seems to be irreleveant or otherwise swamped, I suppose I should spice model this and see what it does? Anyone have an insight?
Anyone have capacitance values for pushback cloth wire vs a similar gauge of pvc?
I note my lone dimarzio single coil has two untwisted PVC insulated cables in a guitar sporting two 4core+shield humbuckers from factory.
I further note that the only guitar I owned that I never felt the need to modify beyond fixing a scratchy pot was a early Maverick X1 that had a twisted pair of wires from each of the two coil over alnico rod humbuckers. I don't know if it was standard, but i understand it to have been a demonstrator at the first UK Maverick dealer and then owned by the son of one of the store owners, so he probably had easy access to quite talented but awkward to engage store luther.
I'm confused as to how or why you're measuring the capacitance of single conductors. You get capacitance when there's a potential difference between two electrical charges, and a single conductor wire, I would think, represents a single charge. Capacitance would come into play when two conductors are near by, but then variables like air gap will determine the capacitance more than the conductors themselves. Regarding capacitance and scatter winding; one conclusion that can be drawn from comparing Strat pickups to Jazzmaster pickups is that what matters for more than inter-winding capacitance is the overall distance from one end of the coil to the other. A typical Strat pickup shows on average 110pF capacitance, where as typical Jazzmaster pickups, which have a similar amount of wire but in a flat and wide geometry rather than tall and thin, have closer to 45pF capacitance. When you have a tall, thin coil, the start and finish of the coil are rather close together, only separated by perhaps 3mm distance, from inner coil edge to outer coil edge. With a flat, wide Jazzmaster pickup, the start and finish are closer to 10mm apart. So you could potentially get Strat pickups closer to that ideal by making the coil wider, or using thicker build wire, but it goes to show that without a dramatic change in geometry, or coil layout, there is a limited potential in terms of how low the capacitance will go. Another reasonable way to lower capacitance, which is sometimes used in industrial applications, is to sections off the coil into divisions, so that you have lots of little stacked coils. That also serves to increase the overall distance between the start and end of the coil, because then the start and end are not merely inside/outside, but top-inside and bottom-outside (or vice versa). Of course, figuring out how to segment a small guitar pickup coil is a tricky proposition. |
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Post by straylight on Jul 1, 2018 0:42:05 GMT -5
I'm not dealing with single conductors, it's pairs all the way. Single+shield, 4-core+shield, tight twisted pair in pvc or cloth, or a loosely coupled pair. However much it is, it's a significant fraction of our 470p nominal load. My multimeter leads are approximately 20pF/M loosely coupled which is enough for me to have to be incredibly methodical when measuring components or cable sections of similar magnetude.
Maybe a better question: Is there a standard length of cable being used in the analysis of pickups here? Should there be?
I can normalise my own production and make reasonable guesses about the wire major manufactures are using if I've had the chance to properly cut something up. But then I run into big contradictions, I've got a PAF clone fitted into a lawsuit-era Jedson (i think this is a Hoshino Gakki ) with a good foot of very thick PVC single+shield. I'm not allowed to dismantle it, but it's quite obvious the cable is of much lower capacitance than any other single+shield I've been near and it's time for me to break out more maths.
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Post by antigua on Jul 1, 2018 11:30:44 GMT -5
I'm not dealing with single conductors, it's pairs all the way. Single+shield, 4-core+shield, tight twisted pair in pvc or cloth, or a loosely coupled pair. However much it is, it's a significant fraction of our 470p nominal load. My multimeter leads are approximately 20pF/M loosely coupled which is enough for me to have to be incredibly methodical when measuring components or cable sections of similar magnetude.
Maybe a better question: Is there a standard length of cable being used in the analysis of pickups here? Should there be?
I can normalise my own production and make reasonable guesses about the wire major manufactures are using if I've had the chance to properly cut something up. But then I run into big contradictions, I've got a PAF clone fitted into a lawsuit-era Jedson (i think this is a Hoshino Gakki ) with a good foot of very thick PVC single+shield. I'm not allowed to dismantle it, but it's quite obvious the cable is of much lower capacitance than any other single+shield I've been near and it's time for me to break out more maths.
I test both with and without the 470pF test load. As for the unloaded case, the resonant peak is measured, and the capacitance is derived from that and the inductance, which is measured with a good LCR meter before hand, and then the pre-determined capacitance of the test device is subtracted from the calculated capacitance. When a pickup comes with a shielded lead wire, I leave it there for testing, since it would also be there is situ. Of course that adds something on the order of 40pF to 70pF for one foot of lead wire, and that's not an ideal situation, but I don't want to modify pickups too much, if at all, in the course of testing. This goes to show why the 470pF loaded test case is more useful, it's more realistic because it adds a larger capacitance that is to be expected in tandem with a guitar cable, and it shows why inductance is a more important metric than either the resonant peak or the capacitance; it's the only meaningful value that will not change from one application to the next. It looks like you might be looking to achieve a particularly high degree of accuracy. I'm not sure what the purpose of that highly accurate data is, but I know that it would make an already tedious affair that much more nerveracking. From a time efficiency standpoint, I think it makes more sense to gather a lot of good data, rather than a little bit of great data, especially when there is (was) no data available at all. |
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Post by straylight on Jul 4, 2018 15:01:33 GMT -5
That's helpful, thanks. I think recording the lenght of cable on the picup tested might be appropriate.
Purpose 1 is my own QC, i'm trying to reproduce a set of pickups consistently based on three of my prototypes I am particularly happy with. Nothing out of the ordinary sound wise, warm and bright extremes of vintage strat sounds and a very overwound single coil, but my construction is slightly different for cosmetic reasons. I don't want my QC to be trying every example i make to order my favourite strat for a week. I should probably decide a length of cable to use for a freshly constructed pickup.
Purpose 2 is taking a client's favourite pickup and matching it to a commercially available replacement or handwinding somehting similarly voiced with a different construction. A particularly infuriating example is finding a covered pickup that has a voicing and string response output that's thin enough to use in an Ibanez S-series, becasue taped pickups and plastic covers are ugly, and locking vibrato abuse is probably a genre of music in it's own right.
Purpose 3 is just better understanding the guitars and pickups i have acquired and made, particularly why they sound the way they do, all of the curiosity.
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Post by antigua on Jul 5, 2018 13:27:13 GMT -5
That's helpful, thanks. I think recording the lenght of cable on the picup tested might be appropriate.
Purpose 1 is my own QC, i'm trying to reproduce a set of pickups consistently based on three of my prototypes I am particularly happy with. Nothing out of the ordinary sound wise, warm and bright extremes of vintage strat sounds and a very overwound single coil, but my construction is slightly different for cosmetic reasons. I don't want my QC to be trying every example i make to order my favourite strat for a week. I should probably decide a length of cable to use for a freshly constructed pickup.
Purpose 2 is taking a client's favourite pickup and matching it to a commercially available replacement or handwinding somehting similarly voiced with a different construction. A particularly infuriating example is finding a covered pickup that has a voicing and string response output that's thin enough to use in an Ibanez S-series, becasue taped pickups and plastic covers are ugly, and locking vibrato abuse is probably a genre of music in it's own right.
Purpose 3 is just better understanding the guitars and pickups i have acquired and made, particularly why they sound the way they do, all of the curiosity.
#1 I should have noted the hookup length and type, though I can say they were never cut shorter than their factory ready length of about 10 inches, plus or minus an inch. I learn as I go. #2 Even if your client has a favorite pickup that happens to have a 8 and 7/16th inch double braid cloth hookup wire, you're going to get a higher variance in capacitance depending on both his guitar cable and whatever he plugs the guitar cable into, so it's not as though you could ever provide any assurances with respect to capacitance in situ. #3 I don't know that I've had any open questions outstanding on account of these issues. |
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