The capacitive coupling of various guitar parts

[antigua]

This doesn't involve pickups directly, but one thing you come to understand is that a pickup is not a standalone determinant of tone, it combines with the loads and capacitance of the guitar in order to produce a final transfer characteristic. To that end, every component along the passive circuit path can be seen as a part of the pickup(s). 

The amount of high frequency response you get out of a guitar pickup is determined the by frequency it resonates at, for beyond that frequency, the signal all but disappears. The amount of capacitance in and across the pickup push the resonance downwards. A guitar pickup usually has between 100pF and 200pF capacitance all by itself, so things like guitar and patch cables stack on top of that.



The resonant peak of a Strat pickup should be 10kHz with it's 100pF capacitance and 2.5H inductance. If you add 500pF by way of guitar cable and other things, the resonant peak drops to 4.1kHz, less than half the initial value. If you have a bad guitar cable, as seen below, the resonant peak drops even further to 3.1kHz. There comes a point where there is no mistaking the loss of high end. Note that true bypass pedals add capacitance, too, since they are essentially and extension of the guitar cable when they're disengaged.



Here's the capacitive contribution of some guitar components, starting lower and going higher. The small components don't add a lot of capacitance by themselves, but it all adds up.





Guitar Components


Hookup wire; two 12" strands laid side by side produces about 5pF.





Twisting them together almost triples the capacitance to 14.4pF






12" Gibson style metal braided shielded hookup wire produces a whopping 75pF capacitance








And import style selector switch, only 2.4pF, not much. American vintage style produce even less, around 1pF.








Male 1/4" plug, 5.0pF








6" patch cable, 28.0pF








6" patch cable with 1/4" female on the end. 37.6pF, so an additional 9.6pF from the female jack.








Typical potentiometer, 9.7pF









Guitar Cables


This is invariably where most of the capacitance comes from.


Fender 18': 547 pF






Monoprice 1/4 10' "instrument cable", 916 pF



So you can see the Monoprice is substantially worse, despite being shorter. A few possible reasons are 1) larger diameter lead wire in the center 2) less insulation between the braded shield layer and the lead center wire 3) capacitive male jacks on either end.

After seeing how bad my 10' Monoprice cable was, I bought this "low capacitance" 10' cable from Amazon... www.amazon.com/gp/product/B00PJ12WYC/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1

They claim "Very Low Capacitance", so what does the survey say!?



411.6pF, or 41pF per foot. Not great, but not as bad as the Monoprice cable. I certainly wouldn't say this is "very low capacitance".



Shielding



First, if the conductor is only in proximity of the shielding foil, you'll get a low capacitance, below 10pF, 5.7pF seen here.






If the conductor is up against the shielding, the capacitance climbs to over 10pF, 12.1pF in this case.






If the shielding encloses the conductor, as is the case with shielded wire, the capacitance almost doubles to 23.6pF

[newey]

Hi, Antigua-

Hello and Welcome to G-Nutz2!

This perfectly illustrates the huge impact that cable capacitance has (as you note, far outweighing everything else).

I find myself wondering if we could quantify, first, the overall capacitance of a typical Strat type guitar, with a basic brand cable, switch pots, etc., as compared to a "best-case scenario", where we would use a low-capacitance cable, wire, no-load pots, and so forth. How much difference can be made through judicious choice of components?

[antigua]

The lowest capacitance cable I have is a five footer at 135pF, and the worst is the 1000pF monoprice cable, so that sort of defines the range you can easily control. Everything else is either hard to change, or would have a minimal impact, anyway. 

I'd say a Strat of a Tele's wiring harness totals somewhere between 30pF to 40pF, if you add up the parts and the lengths of wire. Strat pickups and Tele bridge pickups have generally been 100pF - 150pF, while Tele neck pickups tend to fall between 200pF and 300pF. So with a Strat and that 5' cable, you can come in around 265pF total on the low side, or use a monoprice cable and possibly top out around 1,100pF. I've heard that the Jimi Hendrix style coiled wire contains several nanofarads worth of capacitance, so that would blow the monoprice cable out of the water.

So using this calculator www.sengpielaudio.com/calculator-XLC.htm lets say we have a Strat pickup with 2.5H inductance, and all together our capacitance is on the low side, 265pF, that makes for a resonant peak of 6,183 hertz. That should sound pretty bright. Now lets suppose the capacitance is on the high side, 1,100pF, that puts the peak at 3034.97 hertz. Not  exactly "dark", more like a thick treble that lacks in presence. Suppose you're using a Jimi Hendrix style coiled cable, suppose it's 2,000pF, that bring the resonant peak down to 2175.92 hertz, and that will be darker, and possibly nasal sounding, depending on the Q factor you achieve at that frequency. 

Here's is a tone generator in order to relate these frequencies to heard perception: www.szynalski.com/tone-generator/ . It's not so much that you will hear an emphasis at the peak frequency, because the Q factor is low, it's more like the cut off frequency beyond which you're unlikely to hear anything. If the Q factor is especially high, you do hear emphasis at that frequency. 1 meg tone and vol pots will get you a high Q factor, and this is why people generally prefer the lower 250k or 500k pots to the 1 meg. 

Also, I just measured the capacitance of one of my "true bypass" pedals, a Caline "Pure Sky", and it exhibited only about 10pF to 15pF capacitance, so there's that. 

[antigua]

I just got this 10ft Roland low capacitance guitar cable in, coming it at around 30pF per foot. Not too bad. It also has a very slinky feel to it. Despite its thickness, it's incredibly flexible. I do recommend. 

[antigua]

This is a follow up, I've had a chance to determine what caused the high capacitance in the Monoprice cable, and the low capacitance of the Roland cable...

How capacitance works is, you have opposing electrical charges within a given circuit coming close to one another, and since opposites attract, rather than continue along their way, they stop to make conversation with that opposing charge. The closer the charges are allowed to come one another, the more they attract. With a typical unbalanced guitar cable, the lead wire and the shielding layer are of opposite charges, and so guitar cables are unfortunately also very long capacitors. The trick to reducing capacitance inherent to the cable is to put as much space between the lead wire and the shielding layer, or reduce the surface area of the conductors.

The reason capacitance is bad news for passive pickup electric guitars is because passive guitar pickups, the kind that don't require batteries, are "RLC low pass filters" in principle. The "C" in RLC stands for "capacitance", and pickups are designed to have a particular treble "cut off" point based on a predicted amount of capacitance. When more capacitance is added than was anticipated, the pickup loses high end response, and becomes nasal sounding. Most guitar pickups have about 100 to 200 picofarads of capacitance, and it's expected that a guitar cable will add another 400 to 500 picofarads on top of that. The Monoprice cable in question adds over 900 picofarads capacitance, which is beyond what is anticipated with typical pickup design, and high end response suffers as a result.

First, here is the Monoprice cable. This cable measured almost 1nF for 10 feet of cable. 


You can see that what they did is use a shielded stereo wire for a mono cable. The two lead wires each have a diameter of 0.033":



Here is a cross section view:


This shows that despite the fact that the cable is very thick, the shielding is directly wrapped around the two stereo lead wires. 

You have a double whammy here; first you have a ton of surface area between the braided shielding and the dual 0.033" dia. lead wires, and on top of that, the shielding is closely mated with those wires within the overall thick cable. 






Here is the vastly superior Roland cable, measuring around 318pF:




Looking at the jack, you can see that there is one lone wire, and that there are actually two coats of insulation between the lead wire and the braided shielding; a semi-clear inner layer and a black outer layer.  The lead wire measures 0.028" in diameter, meaning this single lead is smaller than the Monoprice's dual leads, individually:



The Roland cable is the opposite of the Monoprice cable; the smaller single lead wire introduces less overall surface area between the conductive lead and shielding, and on top of that, there is additional insulation between the conductors, all serving  to reduce capacitive coupling. 

The Monoprice "instrument cable" was obviously designed by someone who doesn't know, or doesn't care, about what constitutes a decent guitar cable. Capacitance this high can single-handedly ruin your tone. Avoid at all costs. 


Here are four more Monoprice quarter inch mono cables, two 6" patch cables, a 3' and a 10', all making use of stereo lead wire: 

[stratotarts]

Great stuff! I will have to find one of those Roland cables somewhere... I tested all the ones I have, and they all have ridiculously high capacitance. I prefer a simple thing like a properly designed cable to fancier solutions, like preamps and such, even if they are technically more interesting.

[antigua]

I can appreciate that it's a catch 22; the best cable would have a very tiny lead wire, but that would be prone to breakage. And/or they could out the braided shield further out from the center, but that would probably lead to a very stiff cable. I wonder if they could make a cable that used some sort of conductive liquid instead of copper, or maybe both, conductive liquid to fill any gap caused by broken copper, and then the copper to fill in for any gaps in the liquid.

[col]

This thread might be of interest:

Holy Cap! $100?!?

[antigua]

Here's the site www.undertoneaudio.com/products/vari-cap-instrument-cable  That's pretty cool, I wonder how they got it down to 13pF per foot in the cable portion. $100 is a lot, but I think it might be worth it if the rest of your rig is perfect and there is no other weak link in the signal chain. 

[ms]

Why the emphasis on low capacitance?  What you need is the right capacitance to get the tone you want, and for most guitarists, this is not as simple as "as bright as possible."  Anyway, making the resonance too high can make the sound less bright.  But I do think you might want to use cable with a lower capacitance per foot when you need to play with a longer cable.

[ms]

A wire near the edge of a flat conductor is very much like two wires since the charge in the flat conductor will mostly be along the edge near the wire.  So your result shows the consistency of your measurements since you got almost the same result as two wires.

The method of images (https://en.wikipedia.org/wiki/Method_of_image_charges) is useful for predicting and understanding the effect of a shield.  Of particular interest is the statement "Because electric fields satisfy the superposition principle, a conducting plane below multiple point charges can be replaced by the mirror images of each of the charges individually, with no other modifications necessary."

[antigua]

Dec 13, 2016 7:28:56 GMT -5 ms said:

Why the emphasis on low capacitance?  What you need is the right capacitance to get the tone you want, and for most guitarists, this is not as simple as "as bright as possible."  Anyway, making the resonance too high can make the sound less bright.  But I do think you might want to use cable with a lower capacitance per foot when you need to play with a longer cable.

The main problem with it is that it's not a well controlled value. Unless you have an LCR meter on hand, you don't know how much capacitance is being added, and whether or not a replacement cable is giving you the same capacitance as the last. It's like relying on strings that are oxidized to some particular extent in order to control brilliance. If you like a particular cable, you would have to make sure that subsequent cables used the same wire gauge and shielding profile, which I'm not even sure is possible to determine in many cases.  

You already have tone controls on the guitar and the amp which more more softly attenuate the treble. The use of capacitance moves the resonant peak down, which makes for a tonal aesthetic that Santana, Hendrix and apparently Slash all sought out, but these are guys known for playing blues and rock lead guitar, not necessarily clean and pristine, which is a more commonly desired and versatile base line upon which to shape tone.

I hope to spread the word about RLC resonance, and the fact that added capacitance doesn't merely drain away high end, because this is the understanding most pro-audio guys have, but it leads to misunderstandings like this:


www.guitarplayer.com/accessories/1019/review-undertone-audio-vari-cap-instrument-cable/56006

The big thing I discovered, though, was that a high-cap cable like that doesn’t just act as a low-pass filter. It turns out that as it removes highs, it also creates this bizarre midrange bump—a bump that actually can sound good through some rigs. In fact, with Slash, that mid-bump had become a key ingredient in his tone. His hot-rodded Marshall rig pretty much required a high-cap cable.

The idea of a resonant peak shouldn't be bizarre, and a rig certainly should 'require' a high capacitance cable. A graphic EQ, for example, would allow them to place the 'bump' wherever they want. A capacitance selector such as the one in the product in question would allow them to achieve the same particular bump no matter the pickup being used.

[reTrEaD]

Dec 13, 2016 7:28:56 GMT -5 ms said:

Why the emphasis on low capacitance?  What you need is the right capacitance to get the tone you want, and for most guitarists, this is not as simple as "as bright as possible."  Anyway, making the resonance too high can make the sound less bright.  But I do think you might want to use cable with a lower capacitance per foot when you need to play with a longer cable.

Good question. In my humble opinion the "why" has more to do with the effect cable capacitance has when the guitar volume control is turned down than it does with the effect of cable capacitance when guitar volume control is at max.

There are a lot of guitars without a "treble bleed" network that could (partially) compensate for the horrendous high-cut effect that occurs when the guitar volume control is dialed back. For guitars like that, a cable capacitance that is too low is far more manageable than one that's too high or even "just right" when the guitar volume is at max.

JMO.

[antigua]

The capacitance takes out highs by reducing the resonant frequency, where as turning the volume knob down reduces highs be lowering the Q factor and softening the resonant knee, so they're not strictly working the same way. Due to confusion about the difference, guitarists lump it all together as more treble and less treble, which is too bad because the difference is audible. Damping the Q causes a more muffled high end, while reducing the peak frequency tends toward a nasal, "honk" tone. It's worthwhile knowing the distinction so that a person can most effectively solve the problem.  For example, if the treble sounds nasal, you have to find some way to eliminate capacitance (or otherwise push the resonant frequency higher), but if it merely sounds muffled, higher value pots might be the answer, or it could be a problem having to do with the input impedance of the amplifier. 

[reTrEaD]

Dec 13, 2016 13:43:01 GMT -5 antigua said:

The capacitance takes out highs by reducing the resonant frequency, where as turning the volume knob down reduces highs be lowering the Q factor and softening the resonant knee, so they're not strictly working the same way.

When the guitar volume control is at max, the cable capacitance is directly in parallel with the pickup. So the cable capacitance does lower the resonant frequency and the Q is relatively high because the internal resistance of the pickup is low.

Dialing back the volume control even slightly dramatically changes the equation. Instead of the shift and amplitude of the resonant frequency, the effect of the cable capacitance being part of a high-cut filter is now the dominant consideration.

The reduction of volume in a voltage divider that results in voltage/2 is quite modest. Consider a 500k pot presenting 250k in the top half of the divider and 250k in the bottom half.

Now consider the effect of a 500pF cable in parallel the bottom half of the divider. At 5kHz, that 500pF represents a reactance of roughly 64k. Looks pretty serious without even bothering with the math and trig.

[antigua]

Dec 13, 2016 14:26:51 GMT -5 reTrEaD said:

Dec 13, 2016 13:43:01 GMT -5 antigua said:

The capacitance takes out highs by reducing the resonant frequency, where as turning the volume knob down reduces highs be lowering the Q factor and softening the resonant knee, so they're not strictly working the same way.

Dialing back the volume control even slightly dramatically changes the equation. Instead of the shift and amplitude of the resonant frequency, the effect of the cable capacitance being part of a high-cut filter is now the dominant consideration.

That's a great point. I'll try modelling this with LTSpice later to get a look at the curve differences. 

[ms]

Well, I have a somewhat different take on the tone issue.  If you want to play clean with the bright sound usually identified with clean electric guitar (OK, not most jazz), and want to play without a pre-amp in the guitar and the correct cap before the amp to set the resonance right, then you must play with the volume on 10 if you want to get it exactly right. (Even a treble bleed does not sound right wth the volume reduced.) And you must select a cable with the right capacitance.  It does not require measuring the cap of each of the cables in that pile on the floor; it just requires selecting the one that sounds right.

if you want to play with a lot of distortion, then you probably want to cut treble, and there are a lot ways to do that, and some of them include not even noticing that you did it.

[reTrEaD]

Dec 13, 2016 16:18:14 GMT -5 ms said:

(Even a treble bleed does not sound right wth the volume reduced.)

I won't argue with that, other than to say there is a huge disparity in results, depending on the particular treble-bleed strategy employed.

This thread provides some reasonable insight on the differing strategies:
A better treble bleed circuit

Worth noting is the absurd amount of overcompensation at much lower volume, in the capacitor-only version.  That is somewhat mitigated in the resistor-in-parallel-with-cap version.  More so in John's "improved" version.

Also worth noting, the shift in frequency of the resonant peak.

[stratotarts]

What about the amp? I have a ProCo MusicMan 10 foot cable that measures 380pF. When I plug that into the Cube 80x, I see 1,900pF.

[antigua]

How do you measure the capacitance of the amp's input? I'd think the resistor across in the input would mess up an LCR reading. 

I've currently got a Deluxe Reverb going as my practice amp, and I have felt like capacitance issues have been more noticeable with this amp than some others. I wish it had the same bright switch as the Twin Reverb. I'd mod it, but I'd rather do these pickup studies with the time. 

[antigua]

Dec 13, 2016 16:18:14 GMT -5 ms said:

Well, I have a somewhat different take on the tone issue.  If you want to play clean with the bright sound usually identified with clean electric guitar (OK, not most jazz), and want to play without a pre-amp in the guitar and the correct cap before the amp to set the resonance right, then you must play with the volume on 10 if you want to get it exactly right. (Even a treble bleed does not sound right wth the volume reduced.) And you must select a cable with the right capacitance.  It does not require measuring the cap of each of the cables in that pile on the floor; it just requires selecting the one that sounds right.

if you want to play with a lot of distortion, then you probably want to cut treble, and there are a lot ways to do that, and some of them include not even noticing that you did it.

There's something to be said for serendipity, especially since it all but defines the history of electric guitar. Suppose that's the way you want to operate, I'd favor deliberately seeking out cables that are of known high and low capacitance, to ensure that you have that option, laying somewhere on floor. These Monoprice capacitor-cable all-in-ones certainly satisfy the former. 

[ms]

Dec 14, 2016 7:51:10 GMT -5 stratotarts said:

What about the amp? I have a ProCo MusicMan 10 foot cable that measures 380pF. When I plug that into the Cube 80x, I see 1,900pF.

A tube amp would be about 50 pf,  with the Miller effect amplifying the grid plate capacitance of the 12AX7.  A solid state could be anything, including near zero.  I cannot see why anyone would make it over 1000 pf.

Measuring with an input resistor in parallel should be possible on the par setting of the Extech.

[stratotarts]

Dec 14, 2016 13:34:53 GMT -5 ms said:

Dec 14, 2016 7:51:10 GMT -5 stratotarts said:

What about the amp? I have a ProCo MusicMan 10 foot cable that measures 380pF. When I plug that into the Cube 80x, I see 1,900pF.

A tube amp would be about 50 pf,  with the Miller effect amplifying the grid plate capacitance of the 12AX7.  A solid state could be anything, including near zero.  I cannot see why anyone would make it over 1000 pf.

Measuring with an input resistor in parallel should be possible on the par setting of the Extech.

I cannot see why either. When I read your replies I thought that I forget DC isolation, since the cap meter I'm using (just a setting on the DVM) is skewed or disabled by resistance. But when I put a 1uF in series to eliminate that, I get the same reading. One possible reason could be a clumsy attempt at RFI suppression.

Edit - I think now that it's just the simplistic way that the meter reads capacitance. So I guess this is not the true input capacitance value, it's just the (possibly 1M) input resistance playing with the meter.

[antigua]

JohanHaellgren at MyLesPaul.com suggested disconnecting one of the leads wires. It turns out that disconnecting one of the leads improves the performance of the cable significantly.

Here is a 3ft cable showing 268pF, or 89pF per foot:



Then I clipped the black wire, through the white wire would work just as well.

You'd want to clip the larger of the two, if it so happens that one is larger than the other. You must also clip both ends in order to thwart capacitance.




And then measured again, the capacitance has dropped to 148pF, or 49pF per foot. Still not "top tier", but certainly better than 89pF per foot:



This is certainly a viable way to get much better performance out of Monoprice cables that feature two conductor wires for a unbalanced mono cable. Thank you JohanHaellgren for the idea.

[antigua]

Someone mentioned that the Monoprice cable wasn't ideal for guitar use, although in Monoprice's marketing copy they did call these "guitar patch cables" and suggested they be used for "musical instruments", and upon further investigation it appears that it is probably not a good idea to recommend cable featuring 16AWG for guitar use. Monoprice's actual "guitar cable" uses 20 AWG, and measures 427pF, or 42.7pF per foot:




For a few dollars less (at the time of this writing) Fender offers a guitar cable making use of 23 AWG, and it measures even lower at 315pF, or 31.5pF:


The other factor affecting capacitance is the distance between the shielding and the core wire, and though that can't be see from this vantage point, it seems that there is a strong correlation between low capacitance and smaller wire gauge, which is good to know, if that is all you have to go on.

[wgen]

Dec 12, 2016 22:28:13 GMT -5 antigua said:

This is a follow up, I've had a chance to determine what caused the high capacitance in the Monoprice cable, and the low capacitance of the Roland cable...

How capacitance works is, you have opposing electrical charges within a given circuit coming close to one another, and since opposites attract, rather than continue along their way, they stop to make conversation with that opposing charge. The closer the charges are allowed to come one another, the more they attract. With a typical unbalanced guitar cable, the lead wire and the shielding layer are of opposite charges, and so guitar cables are unfortunately also very long capacitors. The trick to reducing capacitance inherent to the cable is to put as much space between the lead wire and the shielding layer, or reduce the surface area of the conductors.

The reason capacitance is bad news for passive pickup electric guitars is because passive guitar pickups, the kind that don't require batteries, are "RLC low pass filters" in principle. The "C" in RLC stands for "capacitance", and pickups are designed to have a particular treble "cut off" point based on a predicted amount of capacitance. When more capacitance is added than was anticipated, the pickup loses high end response, and becomes nasal sounding. Most guitar pickups have about 100 to 200 picofarads of capacitance, and it's expected that a guitar cable will add another 400 to 500 picofarads on top of that. The Monoprice cable in question adds over 900 picofarads capacitance, which is beyond what is anticipated with typical pickup design, and high end response suffers as a result.

First, here is the Monoprice cable. This cable measured almost 1nF for 10 feet of cable. 


You can see that what they did is use a shielded stereo wire for a mono cable. The two lead wires each have a diameter of 0.033":



Here is a cross section view:


This shows that despite the fact that the cable is very thick, the shielding is directly wrapped around the two stereo lead wires. 

You have a double whammy here; first you have a ton of surface area between the braided shielding and the dual 0.033" dia. lead wires, and on top of that, the shielding is closely mated with those wires within the overall thick cable. 






Here is the vastly superior Roland cable, measuring around 318pF:




Looking at the jack, you can see that there is one lone wire, and that there are actually two coats of insulation between the lead wire and the braided shielding; a semi-clear inner layer and a black outer layer.  The lead wire measures 0.028" in diameter, meaning this single lead is smaller than the Monoprice's dual leads, individually:



The Roland cable is the opposite of the Monoprice cable; the smaller single lead wire introduces less overall surface area between the conductive lead and shielding, and on top of that, there is additional insulation between the conductors, all serving  to reduce capacitive coupling. 

The Monoprice "instrument cable" was obviously designed by someone who doesn't know, or doesn't care, about what constitutes a decent guitar cable. Capacitance this high can single-handedly ruin your tone. Avoid at all costs. 


Here are four more Monoprice quarter inch mono cables, two 6" patch cables, a 3' and a 10', all making use of stereo lead wire: 

I was re-reading this topic and I was thinking about one thing, I installed a Duncan JB humbucker in a guitar once, and it had a quite long 4 conductor hookup wire. Also, these 4 thin wires, together with the ground, were all enclosed in a sort of shielding foil.

I was wondering how this wouldn't make that situation similar to that terrible Monoprice cable in this photo, where you have lead wires enclosed inside some shielding, too.

Maybe the fact that the 4 conductor wires of that pickup are so thin makes the shielding and the lenght irrilevant...?
Thank you very much in advance!

Attachments:

[antigua]

Apr 15, 2017 5:20:26 GMT -5 wgen said:

I was wondering how this wouldn't make that situation similar to that terrible Monoprice cable in this photo, where you have lead wires enclosed inside some shielding, too.

Maybe the fact that the 4 conductor wires of that pickup are so thin makes the shielding and the lenght irrilevant...?
Thank you very much in advance!

   

The four conductor is higher capacitance, but it's only about a foot, which is not as bad as having it the whole length of a guitar cable.

It's more interesting than that, though. Suppose you have the humbucker wired in series, you have two of those wires tied off at the other end of the cable. The signal is between the two coils, and subject to that capacitance, so you effectively have a capacitor to ground in between the two pickups, creating a tiny secondary resonance. It's so small, and of a high frequency, that you can't hear it, but you can see it in bode plots. 

[Charlie Honkmeister]

Apr 16, 2017 1:30:02 GMT -5 antigua said:

Apr 15, 2017 5:20:26 GMT -5 wgen said:

I was wondering how this wouldn't make that situation similar to that terrible Monoprice cable in this photo, where you have lead wires enclosed inside some shielding, too.

Maybe the fact that the 4 conductor wires of that pickup are so thin makes the shielding and the lenght irrilevant...?
Thank you very much in advance!

   

The four conductor is higher capacitance, but it's only about a foot, which is not as bad as having it the whole length of a guitar cable.

It's more interesting than that, though. Suppose you have the humbucker wired in series, you have two of those wires tied off at the other end of the cable. The signal is between the two coils, and subject to that capacitance, so you effectively have a capacitor to ground in between the two pickups, creating a tiny secondary resonance. It's so small, and of a high frequency, that you can't hear it, but you can see it in bode plots. 

Four conductor shielded pickup cables have quite a bit of capacitance to ground.   It isn't normally a big issue since in most cases,  the cable capacitance is the largest value and mostly determines how far the pickup resonant frequency shifts down.  20-60 pF won't matter much in resonant frequency when you are using a 15 to 20 foot cable with anywhere between 650 pF and 1200 pF capacitance.  

Just FYI,  if one were to minimize pickup wiring capacitance,  twisted pairs or just unshielded wires (as in some Bill Lawrence pickups) would work in a shielded control cavity. 

Just as a reminder,  capacitance is inversely proportional to the square (or cube, don't remember which)  of the distance between the conductors.   So shielded cables which have a relatively large distance between any center conductors and the shield foil or braid,  inherently will have less capacitance.  You can see that in RF coax cables, such as RG-59U,  where high capacitance would mean unacceptable loss of signal at high (RF) frequencies.

Because of the distance effect,  if you wanted to gild the lily on low capacitance,  all signal wiring should be run in the center space of a shielded control cavity and as much as possible not run next to the "walls"  or back cover.    Since the capacitance drops off very quickly starting at fairly small distances between conductors,  you won't buy yourself much reduction in capacitance that way.  But sometimes neat, centralized, bundled wiring with not much excess in the control cavity,  can make a small difference, especially with certain styles of clean playing. 

If you lose high end definition before the pickup signal even gets to the amp,  just turning up the treble doesn't always work to get the sound you like for clean playing.  

I'm having to deal with this myself because I'm doing electrically variable capacitance for pickup voicing.   If the inductance of the pickup is relatively  high,  I have to go to really low capacitance values to get a good resonant frequency range and be able to get the resonant frequency as high as I want for hi-fi or Fender/Gretsch tone from the pickup.    Then stray capacitance in the wiring can be an  issue, even with a buffer to eliminate the effect of the cable and amp capacitance. 

[ms]

Apr 16, 2017 9:56:02 GMT -5 Charlie Honkmeister said:

Just as a reminder,  capacitance is inversely proportional to the square (or cube, don't remember which)  of the distance between the conductors.   So shielded cables which have a relatively large distance between any center conductors and the shield foil or braid,  inherently will have less capacitance.  You can see that in RF coax cables, such as RG-59U,  where high capacitance would mean unacceptable loss of signal at high (RF) frequencies.

Because of the distance effect,  if you wanted to gild the lily on low capacitance,  all signal wiring should be run in the center space of a shielded control cavity and as much as possible not run next to the "walls"  or back cover.    Since the capacitance drops off very quickly starting at fairly small distances between conductors,  you won't buy yourself much reduction in capacitance that way.  But sometimes neat, centralized, bundled wiring with not much excess in the control cavity,  can make a small difference, especially with certain styles of clean playing. 

In all the cases relevant here (coax, twisted pair, two parallel wires, one wire over ground plane)  the capacitance per unit length is not dependent directly on spacing, but rather on the inverse of the logarithm of a ratio.  The ratio is spacing to wire radius, where spacing has the relevant interpretation for each case.  It also depends directly on the dielectric constant of the insulator. There are two consequences:

1.  You can not change  by huge amounts because the log function varies slowly with change in the ratio.
2. If low capacitance is your goal, using small wire is just as important as large spacing.

For rf coax cables, the goal is a characteristic impedance allowing efficient transmission.  This characteristic impedance is the square root of inductance per unit length divided by capacitance per unit length.  Very low capacitance is not required.  Coax cable designed for low loss usually has an impedance of 50 ohms.

[Charlie Honkmeister]

Apr 16, 2017 13:42:10 GMT -5 ms said:

Apr 16, 2017 9:56:02 GMT -5 Charlie Honkmeister said:

Just as a reminder,  capacitance is inversely proportional to the square (or cube, don't remember which)  of the distance between the conductors.   So shielded cables which have a relatively large distance between any center conductors and the shield foil or braid,  inherently will have less capacitance.  You can see that in RF coax cables, such as RG-59U,  where high capacitance would mean unacceptable loss of signal at high (RF) frequencies.

Because of the distance effect,  if you wanted to gild the lily on low capacitance,  all signal wiring should be run in the center space of a shielded control cavity and as much as possible not run next to the "walls"  or back cover.    Since the capacitance drops off very quickly starting at fairly small distances between conductors,  you won't buy yourself much reduction in capacitance that way.  But sometimes neat, centralized, bundled wiring with not much excess in the control cavity,  can make a small difference, especially with certain styles of clean playing. 

In all the cases relevant here (coax, twisted pair, two parallel wires, one wire over ground plane)  the capacitance per unit length is not dependent directly on spacing, but rather on the inverse of the logarithm of a ratio.  The ratio is spacing to wire radius, where spacing has the relevant interpretation for each case.  It also depends directly on the dielectric constant of the insulator. There are two consequences:

1.  You can not change  by huge amounts because the log function varies slowly with change in the ratio.
2. If low capacitance is your goal, using small wire is just as important as large spacing.

For rf coax cables, the goal is a characteristic impedance allowing efficient transmission.  This characteristic impedance is the square root of inductance per unit length divided by capacitance per unit length.  Very low capacitance is not required.  Coax cable designed for low loss usually has an impedance of 50 ohms.

Thanks, Mike,  believe you are correct on all counts.  But I did want to give a very general idea of what is involved here.  Introducing characteristic impedance of a transmission line, dielectric constants, etc. wouldn't make a lot of sense to the non-EE or non-physics crowd.  

Generally guitar wiring  (including the center conductor of most cables)  is in the AWG 18-24 range and the absolute difference in radius of the conductors of wires in that range  I wouldn't think would matter very much (not even close to an order of magnitude difference per unit length), especially since most wire is insulated and the insulation is on the same order of thickness as the wire itself,  limiting the minimum distance possible between conductors.    

If you have a link to a formula reference for this effect, it would be great to share for those who want to chase this down in more detail using real data for insulated wire specs.  

-Charlie