Sheilded wire capacitance and other guitar wiring questions

[JWK]

I have a Robin Savoy and I'm changing the pickups. This is a semi hollow guitar with the selector switch in the les paul position, one volume, one tone, and push pull pots for splitting the coils on the two Rio Grande humbuckers. There is a control cavity accessible from the back like a Les Paul, but the shape of the cavity is more like a tele (for obvious reasons). The pickups are way too hot for me and I don't like splitting humbuckers, so I'm pretty much changing out all the wiring and pots.

My tentative plan:

The wires from the humbuckers come into the control cavity. The pickup's ground wire will go straight to my common ground node. The signal wires will go into multi conductor shielded cable which will go to the selector switch and return in the same cable. So will a 3 conductor cable be the best way to do this? My understanding is that the shield will be grounded only at the common ground node. Pots will not have any terminals soldered to the case so that I can more easily switch between 50s wiring and modern, or any other change I might want to make.

I'm also wondering about the capacitance of the shielded cable. This feels like a stupid question, but will using a multi conductor end up with less capacitance than using single conductor for all connections? My thinking is that it might be like using a longer guitar cord. The longer the shielded wire, the more capacitance, is that right? So when using single conductor, it will be three times the length of cable when mixing both pickups. To make it simple, say the distance from the control cavity to the switch is one foot. The neck humbucker needs one foot of cable to get to the switch, the bridge bucker another foot, and the return signal to the jack another foot. BUT, then I thought that it might not matter. Maybe all that matters is the distance each signal wire travels inside the shield. I know someone here must know the answer to this one.

Any feedback on how to best wire this up would be greatly appreciated.

[Steve A.]

If the humbuckers are too hot you might want to look into wiring the coils up in parallel rather than series... or just replace them. (I like the Gibson 490R/490T pickups and you can usually get a used set of them for under $100.)

With multi-conductor shielded cable it is the proximity of the shield to the inner leads which would determine the capacitance. With 3 conductors inside a single shield the capacitance would undoubtedly be less than 3 single conductor cables but you might get interference between the 3 conductors, probably not an issue with the levels in a guitar. FWIW I think that the capacitance in a 20 foot guitar cable is going to be a bigger issue than the 3 feet of shielded cable in a guitar.

Steve Ahola

[ric]

You will want to ground both ends of the wiring to the remote switch, not just one end, or it won't be grounded.

Grounding is only done on one end of signal wiring in a tube amp to minimize potential ground loops that can cause it to oscillate. Inside your guitar this isn't a problem.

[JWK]

You will want to ground both ends of the wiring to the remote switch, not just one end, or it won't be grounded.

Grounding is only done on one end of signal wiring in a tube amp to minimize potential ground loops that can cause it to oscillate. Inside your guitar this isn't a problem.

I'm only referring to the shielding, not the signal wires.

[ric]

I'm only referring to the shielding, not the signal wires.

The 3 conductor wire going to a Les Paul located switch and only grounded at the common ground node sounded to me like the switch and it's, I assume shielded cavity, would not be bonded to the rest of your grounding scheme.

Sorry if I misunderstood JWK.

[Steve A.]

I'm only referring to the shielding, not the signal wires.

In theory you want a single path connecting the ground from the output jack to the guitar grounds and the metal cover or frame of the pots and switches. The Les Paul was designed with 3 segments of bus wire to the 4 pots to reduce the possibility of the wire acting as an antenna.

In ~1998 the original Guitar Nuts site presented the idea of wiring guitars like amps, keeping the grounds and signal paths seperate until connected at a single point, typically the cover of a volume or tone pot.

Until I ran across his site I had treated the grounds and signal paths in a guitar as being interchangeable to keep total wire length at a minimum thinking that it would keep the noise level down. Nope- my wiring harnesses were a lot quieter after adopting that ground scheme. For one thing the various grounded shields and covers run every which way so there is some cancellation of the noise signal received, ending up at the input of the guitar amp.

Steve Ahola

P.S. I think that guitars would be quieter if stereo cables and jacks were used for interconnects. While not balanced by keeping the signal return inside the cable shield it should pick up less noise. (I never got around to wiring a guitar and amp like that to test out the theory.)

You would also need to rewire any FX pedals being used- what a hassle! But just think if Leo Fender had used stereo interconnects in his guitars and amps in the early 50's...

[ric]

In theory you want a single path connecting the ground from the output jack to the guitar grounds and the metal cover or frame of the pots and switches. The Les Paul was designed with 3 segments of bus wire to the 4 pots to reduce the possibility of the wire acting as an antenna.

In ~1998 the original Guitar Nuts site presented the idea of wiring guitars like amps, keeping the grounds and signal paths seperate until connected at a single point, typically the cover of a volume or tone pot.

Until I ran across his site I had treated the grounds and signal paths in a guitar as being interchangeable to keep total wire length at a minimum thinking that it would keep the noise level down. Nope- my wiring harnesses were a lot quieter after adopting that ground scheme. For one thing the various grounded shields and covers run every which way so there is some cancellation of the noise signal received, ending up at the input of the guitar amp.

Steve Ahola

P.S. I think that guitars would be quieter if stereo cables and jacks were used for interconnects. While not balanced by keeping the signal return inside the cable shield it should pick up less noise. (I never got around to wiring a guitar and amp like that to test out the theory.)

You would also need to rewire any FX pedals being used- what a hassle! But just think if Leo Fender had used stereo interconnects in his guitars and amps in the early 50's...

So all guitar shielded wiring is star grounded with the "downstream" end being the one (and only) end grounded? Separate ground wires connect cavity, pot shells, pickup covers etc., all terminating at the jack?

Not to hijack the thread.

[JWK]

So all guitar shielded wiring is star grounded with the "downstream" end being the one (and only) end grounded? Separate ground wires connect cavity, pot shells, pickup covers etc., all terminating at the jack?

Not to hijack the thread.

Not hijacking at all. I read about this on the old (now defunct) Guitar Nuts site. I should have made it more clear that I didn't intend to copy the old Les Paul layout.

To answer your question: Yes, that is exactly right. Star grounding and especially ensuring that all signal grounds are separated from chassis grounds (no soldering pot lugs to the pot case).

I've had to brush up on this guitar wiring stuff in the past couple of days. I keep thinking I'm going to get back into working on amps and then something happens in my family situation and it all goes out the window. So I haven't touched any wiring in 10 years or more, except to wire in a new pickup here and there. Mostly what I was wondering about was the whole multi conductor shielded cable thing. Les Pauls always used single conductor. So I started to wonder about how you could cut down on the cable capacitance. Do you use three single or one multi? But as Steve explained, it's not that simple.

And so I will stick with my original plan, unless someone comes up with a better one.

I will use the existing four conductor shielded cable from the controls to the switch. I will obviously only need three wires. I guess I'll connnect the switch chassis ground lug to the shield on the cable and ground the shield at the star ground. I'll run a ground bus for the two pot cases. I don't see why the switch case and pot cases would have much influence, but while I'm doing everything else I might as well. Tone pot will go 50s style. I tend to like that, especially with 'buckers.

Oh, a really funny thing from last night. I opened up the control area to take a good look and see if I could figure out how he did all that wiring with the push-pull pots and such. I didn't figure it out, BUT.....(wait for it).........................I found the four conductor shielded wire with the shielding connected to NOTHING. A HA HA HA HA!!! He was only using it as a convenient way of getting four wires through to the switch and back. Mega face palm. Too bad there's not an emoticon for a face palm of that magnitude.

[big_teee]

IME, I've found running all the leads in the same shielded cable from Control cavity to the switch, to be the noisiest way.
I've rewired tons of LP type guitars, and I always pull the multi-cable out, and run 3 shielded singles to the switch.
One from the jack direct to the switch, and one each from the switch to each volume pot, or only one if you only have one volume.
Everyone I've done this for swears by it.
Apparently running the 3 wires together, bleed over.
You guys are losing me on the star grounding and grounding on one end.
You must be referring to active electronics.
None of this is necessary for passive pickups.
T

[JWK]

I have not rewired an LP type guitar ever. In fact, I find the design bewildering (considering how knowledgable Les Paul was) and more than a little irritating. I guess coming off of single coils, that little bit of noise left was nothing. Also, now that I think of it, there were very little fluorescent lights being used (compared to later decades), no dimmer switches, not as much RF, etc.

In any case, since you've done a lot of LP guitars, I would like to know about the type of noise you find coming from the multi cables. What differences do you hear after you go to the three singles?

It might be a moot point for me. I don't know if I can fit three single cables through the channel going to the switch of this guitar.

And no, we are not talking about active pups. There are a lot of people who claim they hear a significant reduction in noise when they go to this type of wiring. I can make no such claim personally. It just makes sense to me and my electronics knowledge tells me it certainly cannot make it worse. I have to rewire the whole thing anyway, so why not?

And of course we know the pot terminal has to be grounded somewhere. I don't even know why you said that. Aside from the *possible* advantage of the terminal going to a common ground node, it's much easier to change the tone control wiring from modern to 50s. It's not a factor for everyone, but it is for me.

[big_teee]

Sounds like you have it all figured out.
Was just telling how I do it.
GL,
T

[ric]

With Terry's experience with the multiconductor, maybe a hybrid of old school single shielded as he describes, with this (new to me) ground-your-guitar-like-a-tube-amp way? I think that's what I want to try, when I get a chance. I know all about the can't get into the shop thing. This talking about stuff is it for now.

Best of luck with it. Hope you let us know how it goes.

[Steve A.]

FWIW in the various low-end 2013, 2014 & 2016 Gibsons that I've examined they have used shielded multi-conductor cable to connect the selector switch to the control compartment. These guitars are all noisier than they would be if the cavities were shielded and better wiring techniques used (like individual cables as Terry recommended.)

IMO it is definitely worth it to shield the control cavities, even in guitars with humbuckers. I usually use copper foil tape with the seams soldered so that they don't lift up. Heck, when I'm done you usually can't see any tape at all, just 60/40 solder.

While the humbucker design usually eliminates the 60/120hz hum very well I think that shielding the control compartment is necessary to eliminate the other "gremlins"- those higher pitched static-y noises that I get at home living in a cheaply built, poorly wired 4-plex from 1971.

Unless all of these steps are taken I doubt that you would notice much improvement if the Guitar Nuts wiring techniques were used, most of which are actually pretty easy to implement if you already have 2+ conductor shielded cable going to the pickups. Rather than soldering the signal return leads to the shields going to the pot cases, solder them directly to the CCW terminals (#1) of the volume pots which are tied together and sent by themselves in a single lead to the ground terminal of the output jack. (I usually use a 2 conductor shielded cable grounded at one end with the hot and signal return wires inside.)

The ground shields of the pickup cables would be soldered to the backs of the pots, all of which would be connected from a single point to the "master" pot case which also has the various guitar grounds, and with a single lead going to the ground terminal of the output jack.

As for the tone pots I don't think that separating the signal return from the pot grounds would make much difference at all.

Steve Ahola

P.S. Back in the days of AMPAGE I didn't realize that there was already a very logical numbering scheme in place for the 3 terminals of a potentiometer. We can all agree that the wiper should be terminal #2 but what about the two outer terminals? Well, you can make a usable volume control with just the wiper and the normally grounded CCW "cold" terminal so that should be terminal #1, leaving the normally hot CW terminal as terminal #3. (For a dual-ganged pot I would add the letter A or B to those terminal designations.)

P.P.S. Excuse my lengthy posts in this thread but I've been stuck in the hospital since Tuesday night, bored out of my mind and hopped up on that killer drug vicodin because of excruciating pain caused by side effects of the chemo drug I had been taking. If I can't play my darned guitars I might as well talk about them. FWIW I've been wiring up my own custom harnesses for 35+ years, long before I took soldering iron to guitar amp.

[dai h.]

I usually use copper foil tape with the seams soldered so that they don't lift up. Heck, when I'm done you usually can't see any tape at all, just 60/40 solder.

Steve (or anyone), are there any negative effects on the wood when applying the soldering iron to the copper foil?

re: the ground loops, since currents are so ultra tiny (in a typical passive guitar pickup/cavity circuit) you can't get negative effects from some higher current returns (such as a speaker output return, etc.) or higher current noisy returns (high ripple containing ground portions of the power line) through shared common impedance coupling, but (possibly since I've read of some high profile luthier having some sort of problem with a ground loop) perhaps if you do something weird with the grounds like make a very large area loop (as in a literal big hoop with the ground line) which has unwanted signals induced on it (like a transformer), maybe this can give problems?

(some basics: ) "electronic circuits" as the term implies are made of "circuits", or loops, with a coming and going. When AC or DC (or AC and DC) returns through a ground, (since "real" grounds are made of some material with an R, L, and some C (something else nearby) voltage drops can occur (to varying magnitudes depending on the amount of current flowing, wire/trace/plane,etc. size.)) So (although small), the voltage drops can matter when via ground returns a voltage gets into some place that will cause problems (with noise, instability, crosstalk, plus whatever else), hence why grounding (the particular way you arrange and connect grounds) matters. So generally, you should try to recognize where are the AC and DC loops/paths are, think about the consequences and wire accordingly.

(anyway, I'm just a hobbyist, so I hope I got that mostly right)

[JWK]

Sounds like you have it all figured out.
Was just telling how I do it.
GL,
T

I don't have it all figured out.
I was just saying how I planned on doing it and asking anyone had any better ideas. At least that's what I was trying to say.

Based on your experience, it sounds like single conductor is a better idea. I would still like to know what differences you hear when you rewire a Les Paul. I'm still stuck with the channel that was cut for the wires, so I don't know if I can fit three singles.