All 'yer Favorite Hum and Noise Questions

[melodianchew]

Hello, Fellow GuitarNutzians:

Ive been coming to this, my favorite guitar flavored web site, ever since there was only a GN1, though this is my first ever post. I thank you all retroactively and in future tense, for all your great help and instruction.

I have been dabbling in electronics modification and design and its theory for a long time although in a purely amateur capacity, and with no schooling, nor a mentor, and have unfortunately had to rely on my auto-didactic nature to push me through concepts and learning. I have a greater working knowledge of electronics than I do a theoretical one, born form reading, experience and experimentation. The theoretical lack no doubt as a consequence of a lack of any formal instruction. But I yearn for knowledge of it eagerly.

So, in my famous loquacious nature, I will have probably killed the interests of many prospective experts that might offer opinion, likely abandoning the post by this point due to its verbosity, but I felt like it might possibly help (me) in some fashion if I could first in advance try to give said prospective experts license to expound on a more technical or theoretical level, if they might feel so inclined, perhaps if just for this particular post.

For, although there is a vast wealth of information available on the net to the complete novice on just about any subject, it seems like that instruction or information that is at a more intermediate or advanced level is very often difficult to come by, and it is a light glazing of such that I seek here. I full well understand that the difficulty in providing information that is more advanced is that it requires an assumption of knowledge of basic fundamentals which can be tedious to have to provide for initiates. So, please dont be afraid to be technical.

Now, incidentally, I prefer single coil pickups generally and have had GREAT success in attenuation of the inherent hum and artifacts they so naturally display through the many wiring and shielding techniques that I first learned about for noise reduction here on GNutz, but that success has just brought me more questions actually.

So, The questions in this post are aimed specifically at the particulars of shielding and wiring and best practices of it and why, and my hope here is obviously in taking a shot at getting a much better grasp of some of the theoretical aspects of grounding, hum, noise, and its causes, as they specifically relate to the guitar and its wiring, through posting a range of questions that I have gathered, that I would like to have more clarity on, or which I hope will at least fill a few holes in the container i use for holding such knowledge. At the very least I believe that this topic could foster some interesting discussion. Sorry for the novel, and thanks again:

QUESTIONS:

1) Generally speaking, which side of the circuit is it more important to ensure a quality of a connection for, the signal or the ground side?

2) Which side would benefit from having a larger diameter wire, ground or signal?

3) Shortest leads possible are best right?

4) In which specific connections is attention to wire length most  critical?

5) I have read that in a guitar, the wire diameters need only be of minimal diameter and that using thinner wires helps by providing a smaller antenna for noise since the currents in that circuit are so small, larger wire is not needed and will only introduce capacitance. True, or am I off base somewhat?

6) Would the old solid, and not stranded copper wire type of Ma Bell telephone wires be a good choice for guitar circuits? Being solid and not stranded, it is extremely thin, seems easier to work with, solders and attaches just like component leads, has no twisting or flaying of strands to have to contend with and is easy to strip and tin. And with the recent obsolescence of the trillions of miles of wire available, sometimes free for the taking, it seems like a perfect choice. And if you are lucky enough to be able to happen upon an old defunct Terminal panel or hub, you can sometimes find it in very long lengths and in a huge array of colors. So, given the short lengths needed inside a guitar cavity, isn't it a perfect choice for leads that won't benefit from shielding like the ones going from the jack to the volume pot?

7) Twisting the leads of pickup wires helps with noise right? how tightly twisted?

8) Are the number of twists per inch that are necessary in a pair of twisted wires a function of the wavelength of the noise signals likely to induce into the wire?

9) I have seen some posts characterize the ground wire connections that normally exist, in say, a standard strat wiring scheme, that are connected between tone and volume pot shells, as unnecessary, IF shielding is present and continuous under pot mounting points. They were characterized as potential ground loops and if the whole cavity was shielded were better left off. Then another post claimed best practice was to consider them signal returns and therefore necessary and best practice is NOT to rely on shielding for that purpose. So which is more true and what factors determine making the best decision between the two?

10) I shield the inside of my jack route as well, is this a best practice? Or is it really unnecessary if the lead is shielded coaxial wire?

11) When using shielded leads, it is better to use a two wire with braided shield, as in1 signal, 1 ground, and a braided shield that's grounded on one end, or, is just a simple single signal wire wrapped in a shielded braid that is used as ground a better choice for the lead going from jack to volume pot?

12) Which side is it best to attach the braided shield to ground to in a shielded wire, the jack side or the pot side and why?

13) When shielding the cavity of my guitar i generally prefer copper tape with a conductive adhesive. How critical is ensuring a uniform measure of low resistance between any two points of the shield? How will that affect things?

14) Am I wasting my time in efforts to guarantee much more uniform conductance between tape layers if i will lay down in the cavity and across the pick guard, a continuous flat bunch of thin bare wire strands that i have spanned and are touching across all of the pieces of the tape sections that i cover with another piece of copper tape to hold it all cleanly down in the cavity?

15) I work hard to achieve a small continuous "gasket" of the copper tape i use to shield the cavity with that I fold outside of the holes and lay flat against the top of the guitar such that the shielding of the copper tape on the pick guard will touch and lay flat against it so as to maintain a better continuous  connection around the whole border of the connection point between the pick guard and the guitar body. Is this level of meticulousness helping much?

16) Is a shield that i have gone to this much trouble to ensure the continuity of one that might make the keeping of the ground wires between pot shells, that are normally used as signal returns, unnecessary?

17) How detrimental are cold solder joints to the tone of the guitar?

18) Why does hum get louder or quieter based on the direction i am pointing my guitar?

19) Why does hum gets quieter when i touch the strings or metal pieces of hardware?

20) Why would the hum get louder if i am touching the strings or metal of my guitar?

21) If we are preserving the ground wires between pot shells as signal returns, doesn't this destroy my attempts at achieving a star type of grounding?

22) Why aren't the connections between the pots made by their shells in their attachment to the pick guard shield not considered ground loops?

23) Should I be concerned with a potential for corrosion that i might induce in a circuit at connections where the metals differ? is it the amount of current running through the circuit that determines the extent of the corrosion potential? is the current in a guitar circuit too low to worry about this condition? does having the solder in a joint of two differing metals help mitigate such fears?

24) In order for ground loops to exist is it a difference of resistance or impedance between the two different connections that is causing it?

25) Now that I have exposed just how profound my ignorance on this subject is, is there anything else you think I might like to need to know about it?

Ok, I'm gonna be a real Captain Obvious here but, one might answer any of the questions by simply typing the number the answer pertains to then answering, like in this fashion, for instance as if this might have been your reply to #25 :

"25) Yes, you ARE quite profoundly ignorant, and SO profoundly so, that I have started to consider that maybe ignorance DOES also imply an existing component of stupidity, and therefore have decided I should not even bother trying to answer for risk of confounding you even further by providing you any other details."

(sorry, the class clown in me just couldn't resist)

one need answer only one or all of these questions...

Thank you for all of your help,

Scott

The RedneckSage

gear:

every unnecessary note possible on my 1997 Frankenstratosquire "double plus deluxe" with large head stock and maple neck with mismatched single coil pickups through a modded '65 Gibson Lancer RVT.

[stevewf]

Let's form a "Classroom for the Ignorant." I'll sit in the front row... humming.

And from that front row seat, I'll add a Q of my own, perhaps related to #22:

26) Can't a shielded cavity be considered a source of infinite ground loops?

[newey]

20+ questions? This may take a while, can't tackle them all at once.

1) Generally speaking, which side of the circuit is it more important to ensure a quality of a connection for, the signal or the ground side?

For electrons to flow, we need a circuit. All the connections which make up that circuit are equally important, becuase if any of them fail, then we don't have a circuit. Also, when you say "signal or ground side", there are 2 issues. First, the signal requires both a "hot" and a "not hot" connection- or no circuit, as above. Second, "ground" is technically a misnomer, we say "ground" or refere to a "-" connection, but our guitar pickups produce an AC signal; "hot" and "ground" are DC terms which do not really apply, it's just a convenient shorthand to speak about things.

2) Which side would benefit from having a larger diameter wire, ground or signal?

See above.

3) Shortest leads possible are best right?

So long as one is not stretching or pulling on a too-short connection, the answer is yes. However, a bit of extra length isn't going to make any difference, noise-wise.

4) In which specific connections is attention to wire length most critical?

This is not a critical issue, again, so long as you're not pulling on anything to get a wire to reach where it needs to be.

5) I have read that in a guitar, the wire diameters need only be of minimal diameter and that using thinner wires helps by providing a smaller antenna for noise since the currents in that circuit are so small, larger wire is not needed and will only introduce capacitance. True, or am I off base somewhat?

I have never heard that and it sounds like nonsense to me. It is true that one doesn't need large diameter wire, but that's not because of any potential for noise, only that smaller diameter wire is both cheaper and easier to work with. I use either 24 or 22 gauge wire, anything smaller gets harder to work with as far as soldering it. The only reason to go any bigger than that would be if one was trying to keep something "vintage correct"

6) Would the old solid, and not stranded copper wire type of Ma Bell telephone wires be a good choice for guitar circuits? Being solid and not stranded, it is extremely thin, seems easier to work with, solders and attaches just like component leads, has no twisting or flaying of strands to have to contend with and is easy to strip and tin. And with the recent obsolescence of the trillions of miles of wire available, sometimes free for the taking, it seems like a perfect choice. And if you are lucky enough to be able to happen upon an old defunct Terminal panel or hub, you can sometimes find it in very long lengths and in a huge array of colors. So, given the short lengths needed inside a guitar cavity, isn't it a perfect choice for leads that won't benefit from shielding like the ones going from the jack to the volume pot?

It's fine to use old solid telecom wire. I prefer working with stranded wire as it's more flexible tahn solid core, but either one is fine If reusing old wire, check it for continuity to be sure it's all intact under the insulation, although that's usually more of an issue with stranded wire. With solid wire, it's usually visually obvious if there's an issue.

7) Twisting the leads of pickup wires helps with noise right? how tightly twisted?

Doubtful that it makes any difference in a passive guitar circuit (it does matter in higher-powered things like amps). But it won't hurt to do so.

8) Are the number of twists per inch that are necessary in a pair of twisted wires a function of the wavelength of the noise signals likely to induce into the wire?

Got me. I've never bothered to twist the wires in any guitar I've wired.

9) I have seen some posts characterize the ground wire connections that normally exist, in say, a standard strat wiring scheme, that are connected between tone and volume pot shells, as unnecessary, IF shielding is present and continuous under pot mounting points. They were characterized as potential ground loops and if the whole cavity was shielded were better left off. Then another post claimed best practice was to consider them signal returns and therefore necessary and best practice is NOT to rely on shielding for that purpose. So which is more true and what factors determine making the best decision between the two?

OK, I'm still trying to wrap my head around the phrase "more true", but in general ground loops are not a cause for concern (despite what John Atchley wrote on the original guitar nuts site). I oridinarily do not solder things to the backs of pots, I use a star-grounding scheme to avoid that (not becuase of ground loops but to avoid destroying pots). But it you're going to ground to the backs of pots, I would definitley run separate connections rather than relying upon the shielding.


OK, that's about half of them . . .

And:

Hello and Welcome to G-Nutz2!

[gckelloch]

To add to what newey covered, SC EMI (hum) is generally going to be much louder than whatever RFI noise coming from the control cavity. Any wire connected to the pickups can add to EMI, but cavity shielding will do very little to reject it. My understanding is the total mass of the coil is what determines the EMI potential, so a wire with the same mass as a pickup coil could increase noise as much as ~6dB, depending on its orientation to the EMI source, and the permeance of the pickup core alloy. That's one reason to keep wire runs short and thin, but I also wouldn't want to use thinner than 24AWG.

I'd suppose twisting wires could offer some potential EMI cancelation. Not a difficult task. I'd think a tighter wind is better, but I doubt it makes much difference compared to the pickup coil EMI. I wouldn't bother shielding the jack cavity, but it couldn't hurt if it doesn't short.

Shielded wire does generally have higher capacitance than two single wires, but not much more at those lengths-- maybe 1-~20pF. I'd just twist two wires.

Cavity shielding can be effective against RFI, but I don't think Hi-Z pickup coils significantly pick that up. Again, EMI will be much louder. Use Al or Cu tape, or Carbon paint in the control cavity for that. I've used Al tape under the pickups, but Cu tape will actually reduce the higher EMI harmonics more at thinner widths, while 5~10 Al tape layers under the pickguard around the pickups will reduce the harsh upper-mids without affecting the highs. You could try layering ~10 or so Cu pieces under the pickups, but it might have some effect on tone if close to the coil on the sides. One experiment I saw showed that a thin Cu pickup cover has almost no effect on pickup tone but to very slightly raise the resonance freq, yet it did significantly roll off the upper EMI harmonics. So, I wouldn't be concerned as long as it doesn't short on the pickup leads. I guess it should be grounded to sink any EMI the coil might pick up?

To experiment, you could invest in a roll of Cu tape. Layer 10 strips. Place it behind a pickup and listen to how much it affects the EMI harmonics. Then try 20 strips. See what you think. The idea is that it will make the most difference when it significantly reduces the EMI harmonics down in the 2kHz range. It shouldn't affect the pickup tone at all because it's too far from the string vibrations behind the pickup for the EMI disturbing eddy currents to affect the string induced magnetic vibrations within the coil. Another trick is to do the same thing with a thick Al pie tin. Might be easier to somehow cut that up and tape it under the pickups. I've tried that with 1/10" thick tin and a P90. Made a big difference,

So, I leave off at Q 13.

[newey]

Dec 20, 2022 5:10:05 GMT -5 melodianchew said:

13) When shielding the cavity of my guitar i generally prefer copper tape with a conductive adhesive. How critical is ensuring a uniform measure of low resistance between any two points of the shield? How will that affect things?

I also use copper tape with conductive adhesive. It's much easier than trying to solder pieces of the shield together or folding the copper over to make contact with the next piece. So long as there is continuity between the various pieces, you're fine. Your meter will typically show a few Ohms resistance, < 20Ω, typically.

14) Am I wasting my time in efforts to guarantee much more uniform conductance between tape layers if i will lay down in the cavity and across the pick guard, a continuous flat bunch of thin bare wire strands that i have spanned and are touching across all of the pieces of the tape sections that i cover with another piece of copper tape to hold it all cleanly down in the cavity?

Yes, you're wasting your time. The copper shielding tape is enough, provided it's all continuous, as above.

15) I work hard to achieve a small continuous "gasket" of the copper tape i use to shield the cavity with that I fold outside of the holes and lay flat against the top of the guitar such that the shielding of the copper tape on the pick guard will touch and lay flat against it so as to maintain a better continuous connection around the whole border of the connection point between the pick guard and the guitar body. Is this level of meticulousness helping much?

Not sure I fiollow what you're doing here. You should run the copper tape up out of the cavity and onto the body a little bit to contact the underside of the pickguard shielding. If it covers a hole, fine, I'm just going to screw through the shielding there anyway. But I don't worry about getting it out to the holes, it should still be making contact just fine.

16) Is a shield that i have gone to this much trouble to ensure the continuity of one that might make the keeping of the ground wires between pot shells, that are normally used as signal returns, unnecessary?

I think we answered this above. No. Ideally, we want our shield and signal connections to be separate until we get close to the jack barrel connection.

17) How detrimental are cold solder joints to the tone of the guitar?

Tone isn't the issue. Failure of the joint and/or poor connectivity is the problem.

18) Why does hum get louder or quieter based on the direction i am pointing my guitar?

Because the noise is highly directional. The wire wound around in your pickups acts like an antenna. I don't know if you are old enough to remember TVs with "rabbit ear" antennas, but one often had to reposition the rabbit ears to get good reception. Sort of the same thing here, except this is reception we don't want.

19) Why does hum gets quieter when i touch the strings or metal pieces of hardware?

Because your string/bridge ground wire is grounding your body.

20) Why would the hum get louder if i am touching the strings or metal of my guitar?

It should do the opposite, get quieter. If it gets louder, this would indicate a poor connection on the bridge/string ground.

21) If we are preserving the ground wires between pot shells as signal returns, doesn't this destroy my attempts at achieving a star type of grounding?

Well, you could certainly use the back of a pot as the site for your star ground, but one of the main reasons for star-grounding is to avoid having to solder to the backs of pots. With a star ground, I don't solder anything to the pots, it all goes to the star ground point. The shells of the pots get grounded via contact with the shielding, via the shaft of the pot.

22) Why aren't the connections between the pots made by their shells in their attachment to the pick guard shield not considered ground loops?

Somewhere, ChrisK had a great explanation of why we shouldn't worry about ground loops. I'll have to try to dig that out. But a ground loop in the shielding will never be an issue because it's not carrying signal. Anything that's not in the signal chain can't be adding any noise to the signal.

[reTrEaD]

Dec 20, 2022 12:11:45 GMT -5 stevewf said:

Let's form a "Classroom for the Ignorant." I'll sit in the front row... humming.

And from that front row seat, I'll add a Q of my own, perhaps related to #22:

26) Can't a shielded cavity be considered a source of infinite ground loops?

Any shielding needs to be connected to the ground circuit at a single point, preferably at, or just before the output jack. Signal-carrying ground should not use shielding to complete the circuit.

[Yogi B]

Dec 20, 2022 5:10:05 GMT -5 melodianchew said:

3) Shortest leads possible are best right?

4) In which specific connections is attention to wire length most critical?

Shorter is technically better, but in a passive setup absolute shortest path efficiency isn't critical: there's already a far larger length of wire contained within the pickups — very roughly, about 2 miles for a set of Strat pickups.

Where this can be more important is avoiding crosstalk between the input & outputs of high gain active circuitry, e.g. an on-board fuzz or a preamp for an electromagnetic sustainer, in order to avert feedback.

9) I have seen some posts characterize the ground wire connections that normally exist, in say, a standard strat wiring scheme, that are connected between tone and volume pot shells, as unnecessary, IF shielding is present and continuous under pot mounting points. They were characterized as potential ground loops and if the whole cavity was shielded were better left off. Then another post claimed best practice was to consider them signal returns and therefore necessary and best practice is NOT to rely on shielding for that purpose. So which is more true and what factors determine making the best decision between the two?

What really matters here is if the connections between the pots are forming part of the signal path or not. That is, if the relevant terminals of the pots have an actual wire path to the output jack ground, then the pot bodies only form part of the shielding and it's fine to rely upon the contact connection with the rest of the pickguard/cavity shielding.

Whereas, if the pot's terminals are grounded only via a direct connection to the casing, using an actual soldered wire joint between the cases (and also ground) is better than relying upon the shielding alone to carry the signal.

11) When using shielded leads, it is better to use a two wire with braided shield, as in 1 signal, 1 ground, and a braided shield that's grounded on one end, or, is just a simple single signal wire wrapped in a shielded braid that is used as ground a better choice for the lead going from jack to volume pot?

I don't know about best practice, but if I were using shielded two conductor wire, I'd probably connect both ends of the shield: using it as the connection between the main cavity shielding & the output jack.

12) Which side is it best to attach the braided shield to ground to in a shielded wire, the jack side or the pot side and why?

Following on from the previous answer: this seems like a pretty rare occurrence, as you'll usually only really use shielded wire for connections between separate cavities, and you'll be wanting to connect the shielding of the two cavities together.

If it is ever applicable, then I'd opt for the jack-side grounding — you want the shielding grounded and the lowest impedance connection to ground will be via a direct connection to the sleeve of the jack, rather than via whatever means the pot is grounded.

15) I work hard to achieve a small continuous "gasket" of the copper tape i use to shield the cavity with that I fold outside of the holes and lay flat against the top of the guitar such that the shielding of the copper tape on the pick guard will touch and lay flat against it so as to maintain a better continuous connection around the whole border of the connection point between the pick guard and the guitar body. Is this level of meticulousness helping much?

Certainly multiple connections between cavity shielding & pickguard shielding is preferable to relying upon a single point, but having a continuous ring on both the face of the guitar and the underside of the pickguard is probably overkill.

Dec 21, 2022 7:29:18 GMT -5 newey said:

[In response to the prior quote.]

Not sure I follow what you're doing here ... If it covers a hole, fine, I'm just going to screw through the shielding there anyway.

By "holes", I think melodianchew was referring the body cavities, not screw holes.

Dec 20, 2022 5:10:05 GMT -5 melodianchew said:

16) Is a shield that i have gone to this much trouble to ensure the continuity of one that might make the keeping of the ground wires between pot shells, that are normally used as signal returns, unnecessary?

I think this is covered by the answer to question 9.

Dec 21, 2022 7:29:18 GMT -5 newey said:

Dec 20, 2022 5:10:05 GMT -5 melodianchew said:

19) Why does hum gets quieter when i touch the strings or metal pieces of hardware?

Because your string/bridge ground wire is grounding your body.

And/or another theory.

Dec 21, 2022 7:29:18 GMT -5 newey said:

Dec 20, 2022 5:10:05 GMT -5 melodianchew said:

20) Why would the hum get louder if i am touching the strings or metal of my guitar?

It should do the opposite, get quieter. If it gets louder, this would indicate a poor connection on the bridge/string ground.

Alternatively, it could indicate that the string/shield ground is connected to the tip (hot) of output jack e.g. if the connections have been accidentally reversed.

Another possibility is pickups that don't separate their shield & signal grounds (e.g. PAF's with vintage braided wire) wired with reverse phase or in series with another pickup. In this case it's very likely that you'll inadvertently short one or all pickups, but when that doesn't occur you again have a shield connection that is connected either directly to hot or partway through a series stack and thus when touched will cause noise at the output.

[melodianchew]

I'm sorry for how much my ignorance is showing and thank you so much for the time and attention, I sure learned a lot.

[melodianchew]

To all who have and will reply to this post:

Thanks for the warm welcome here to GNuts and I am sorry for the slow response to all of your answers as I didn't realize I had actually had any replies because when I clicked on my post it only took me to my original question and didn't show any replies. I had not yet figured out how to check on if I had received any. I was going to try to reply with thanks to each of you individually for your attention but I wasn't sure if that would be appropriate or not and was afraid its redundancy might just serve to clog the post with unneeded chaff. So, I figured it best to thank you all in this one reply.

It would be hard to overstate how much help your posts have been and I surely do appreciate all who took the time and provided the attention that you have given me with your quite informative answers. Going through the novice stages of any newly learned skill is painful for anybody but I would say even a little more so for aging puds like me as when you get a little older the human resource pool from which you might draw on such helpful entities as mentors or tutors for advice on these subjects can be thin indeed.

I appreciate your collective patience with my ignorance, and I promise to do my best to try to exceed what could be expected from someone with my "special" level of cognitive ability... Ha ha.

Thank you.

[melodianchew]

Dec 22, 2022 5:27:14 GMT -5 Yogi B said:

[abbr data-timestamp="1671625758000" title="Wed Dec 21 2022 04:29:18 GMT-0800 (Pacific Standard Time)" class="o-timestamp time"]Dec 21, 2022 at 4:29am[/abbr] newey said:

[In response to the prior quote.]

Not sure I follow what you're doing here ... If it covers a hole, fine, I'm just going to screw through the shielding there anyway.

By "holes", I think melodianchew was referring the body cavities, not screw holes.

Yes, thank you sorry for the confusion, I WAS in fact referring to the body cavities as a "hole." And incidentally, what I meant by a continuous gasket was that I simply continue the shielding tape past the top edge of the route cavity by folding it over onto the face of the guitar where the pick guard will have contact with it, and making a continuous strip about a 1/4 in. wide (the gasket) around each cavity.

My initial thinking was a guess that the impedance of the connection anywhere in the shield should be as low as possible and I wasn't sure exactly how reliably uniform the connections across separate pieces of tape might actually be and also wasn't sure exactly how reliable the conductivity of the adhesive was going to be so, I guessed it might have been worth it to just provide all of the pieces as many points as possible with which  they could make solid contact but now I see that you have said it is probably overkill, so, ok that's good to know that I need not be quite so obsessive about it. Thank you.

[newey]

I didn't realize I had actually had any replies because when I clicked on my post it only took me to my original question and didn't show any replies. I had not yet figured out how to check on if I had received any

That's odd, unless you didn't refresh the page. But ordinarily, I (or one of the others who replied) would have "tagged you", like this, melodianchew. Don't know why no one did so, but if someone had, then you would have a notification in your profile the next time you logged in.