questions about wiring and shielding Squier CV Mustang

[OnnoP]

I am modding a Squier CV Mustang and amongst many other things, I want to slightly upgrade the stock shielding. My Mustang will also get a Duncan Hot Rails in the bridge and a Duncan Quarter Pound Flat in the neck, so basically it's sort of a Cobain style mod, and although I haven't opened up my guitar yet, I have a pretty good idea of the type of shielding present in a stock CV Mustang.

Basically the body cavities are covered in shielding paint, the paint in the pickup and slide switch cavities is connected to the paint in the control cavity with a ground wire and there's a strip of aluminium foil on the underside of the pickguard that basically only shields the slide switch area.

I want to perhaps add a few extra layers of shielding paint and make sure it's all finished neatly (because I've seen from a few YouTube videos that the shielding paint on the CV Mustangs can be very sloppy / unevenly applied) and replace that stock aluminum foil with copper tape and also add copper tape around the pickup holes on the underside of the pickguard to shield the pickup cavities.

But I need to know if the copper tape needs to make contact with the slide switch housing, or if the slide switch housing needs to be isolated from the tape. I am not an expert on guitar wiring and shielding to say the least, I only know that the wiring diagram for a JagStang (which I will be using) shows that on both the slide switches one of the lugs has a wire attached that is soldered to the slide switch housing.

I assume that has something to do with grounding, and that planted the idea in my head that contact between the slide switch housing and the shielding tape on the underside of the pickguard might create some sort of ground loop.

I also would like to know how the connection between the back of the volume pot and the bridge thimble is made in a stock Squier CV Mustang: is there a hole running from the control cavity to the hole that the bridge thimble resides in? And if so, and there is a wire running from the back of the volume pot to the bridge thimble, how is it connected to the bridge thimble? Is the copper inner wire wrapped around the thimble?

Any input / assistance will be much appreciated!

[OnnoP]

I also need to add that in my current plan, the shielding paint in all the body cavities will spill over the edges, to make contact with the copper tape on the underside of the pickguard and also with the metal control plate. The CV Mustang that I saw in a YouTube video didn't appear to have the shielding paint spill over the edges, at least not with regards to the pickup and slide switch cavities, which made me think that maybe the stock aluminum foil on the underside of the pickguard is grounded by contact with the slide switch housing and that the shielding paint in the cavities therefore can't make contact with the aluminum foil to prevent a ground loop. Does that make any sense? Again, any input will be much appreciated!

[OnnoP]

Also maybe good to mention my current understanding of how the shielding / ground path will run:

ground of the sleeve of the output jack - via the metal control plate - to the tone and volume pot - the metal control plate makes contact with the shielding paint spilling over the control cavity, so the shielding paint in the control cavity is grounded - the wire connecting the control and bridge pickup cavities makes sure that the shielding paint in the bridge pickup, slide switch and neck pickup cavities is grounded and because that paint spills over the edges, contact between the paint and the copper tape on the underside of the pickguard is made and thus that tape is also grounded. I believe this creates a single grounded shield with no loops, but do correct me if I'm wrong, and again, I really need to know how the slide switch housing fits into all this. THANKS!

[timtam]

The shielding needs to be grounded in order to function as a shield. Usually done by wire. But can be done by contact with anything else that is itself grounded (eg the grounded control plate). The components' bodies (switches and pots) also need to be grounded. The pot bodies are grounded by being on the grounded control plate. Ground is ground in a guitar. So the components can make contact with the grounded control plate, grounded shielding, or have their own ground wire. Or all of the above.

There is no such thing as a hum-producing ground loop in a guitar. Despite what one pickup manufacturer (only) says on their website - who when challenged has refused to prove their assertion with the simple experiment required. There is no potential difference between ground points in a guitar, as there is when a physical ground loop between mains equipment causes hum (the potential difference is necessary for current to flow in the ground lines, producing the hum) . So having a physical ground loop in a guitar is not issue. So there is no notion of a required, single 'ground path'.

[OnnoP]

@timtam

I do sincerely appreciate your reaction, so thank you, but I must admit that it isn't quite the response I was looking for, without making any claims into the correctness of the info provided. My very basic knowledge of guitar shielding basically comes from this:

https://humbuckersoup.com/proper-guitar-grounding/

And there the possibility of problematic ground loops is mentioned, and it also has been in countless posts I've read of people talking about noise and hum after (re)wiring their electronics and assuming they had created a ground loop as the cause.

To be honest I'm not sure what to do with the notion that said ground loops don't exist in guitar electronics, other than to say that this post wan't meant to launch a discussion on the merits of that very principle. I mean I understand that if you nevertheless feel that that is the case, then my worries about creating one would be unfounded, but I'm hesitant to dismiss countless mentions of possible problematic ground loops in all kinds of articles and forum posts.

I do take away from the info provided that the slide switch housing indeed needs to be grounded, so that's one thing...

[timtam]

You will find far more people saying that in their experience (consistent with electrical circuit theory), hum-producing ground loops don't exist in guitars.

But guitar wiring web sites are generally not going to fill their pages writing about something that doesn't exist. So all the sites that post wiring information but don't talk about ground loops need to be counted against the small number that do. It's one of those myths that has hung around in guitar circles for a long time. But ask the question in any technical guitar forum and you'll get the answer I gave you.

The site you linked coincidentally presents exactly the same two supposed 'ground loop' scenarios as the notorious pickup maker's site I mentioned. Best guess ? ... he just googled/copied that information without testing its assertions.

The site also incorrectly says that the main reason for guitar grounding is electrical safety. In fact guitar grounding contributes pretty much nothing to electrical safety. We talked about that recently here. A correctly grounded guitar will not stop you getting shocked. In fact it creates some shock scenarios.

What wiring novices suggest as the possible cause of their wiring problems tells you nothing about the actual cause. Probably the most common "problem" post in history is the "Noise goes away when I touch the strings - I have a grounding problem". Whereas noise reducing when you touch the strings actually means that your grounding is correct (the grounded strings are grounding you).

Look at the conditions that cause actual ground loops (plenty of audio engineering sites on that, from studio electrical engineers). Ask yourself if those conditions - the differences in ground potential I mentioned - exist in a guitar.

Or ask yourself why Fender seems to flip a coin when it designs the ground wiring for guitars with metal plates (jags, mustangs, teles) ? The grounded metal plate grounds the pot bodies ... but sometimes Fender also has wires grounding the pots as well. Creating a physical ground loop exactly as described in the Ground Loop 2 scenario in your linked site. But it doesn't matter ... because hum-generating ground loops aren't a thing in guitars.
American Performer Mustang - wired ground between pot bodies on metal plate:
https://www.fmicassets.com/Damroot/Orig ... ustang.pdf
Vintera Mustang - no wired grounds between pot bodies on metal plate:
https://www.fmicassets.com/Damroot/Orig ... ustang.pdf

Or do the simple experiment that that one pickup maker who talks about ground loops refused to do. Wire your Mustang like the Am Performer above (a physical ground loop), record the noise floor, then cut the wire connections and record again. Compare the two noise levels.

[Futuron]

For the question regarding the thimble ground connection - from memory, there is a wire that goes from the control cavity through a tiny little tunnel to the thimble cavity, and the short length of exposed bit of wire is simply jammed between the wall and the thimble, thus making electrical contact with it.

[OnnoP]

@ timtam,

Sorry for the late reply: I had the ''notify me when a reply is posted'' checkbox on, but got no notification in my email inbox, so I had assumed no one had replied anymore.

Thank you again for your time and effort in educating me on this subject. You make your case convincingly, I must admit that. And funny that you mention Fender's own occasional pot ground wiring in guitars with metal control plates: I found several forum posts on several forums of people claiming they had discovered a factory applied ground loop in a Fender offset due to their guitars having that specific wiring (and of course complaining about how it could be that arguably the world's no. 1 guitar manufacturer could make such a ''mistake'').

I guess it's one of those discussions that will go on forever, because the misinfomation / myth will no doubt remain to be found everywhere online forever.

In selecting new pots I researched the use of mini pots vs regular pots and the quality difference between brands, and came across countless discussions going back decades mentioning the superiority of CTS and Bourns full sized pots vs the ALPHA mini pots standard in Asian guitars, and all true tech guys claimed that if the specs are truly 100% identical, there should be no difference in sound, and yet many people claimed that their guitars suddenly came alive after putting in full size CTS pots, and relating that perceived audible difference not to individual pot spec variation, but to overall brand quality and were very aggresive in defending that viewpoint. Seems like a similar endless discussion. But let us not go there

And @ Futuron,

Thank you very much for the info: I had hoped there would already be a hole / tunnel, and not a slot going over the top of the body as some vintage Mustangs have (much neater that way). Plus that's a difficult one to drill yourself and I had hoped to make all my customizations without drilling into any wood or metal.

As far as the wiring is concerned, I found the official Fender wiring diagrams for the Cobain Mustang from a few years back and the Jag Stang diagram (viewtopic.php?t=97914) and have created one for my guitar based on those, but I have a few questions remaining.

Here it is: [img]file:///C:/Users/OP/Desktop/Squier%20CV%20Mustang%20wiring%20diagram%20(based%20on%20CB%20Mustang)%20V2.jpg[/img]

There are two connections on the slide switches that I colored pink and one connection that I colored purple. The pink ones are the wires that connect the ground from the switch lugs to the switch housing: those are present in the Jag Stang diagram, but not in the Cobain Mustang diagram and the purple wire connecting two of the center lugs of the bridge pickup switch is present in the Cobain Mustang diagram, but not in the Jag Stang diagram.

I assume both diagrams are meant to provide the same style operation, so why these differences? Or is it due to the exact point about grounding that member timtam has been making, and is the switch housing connected to ground anyway through contact with the shielding foil on the underside of the pickgard, so that it makes no difference if the pink wire connections are made or not? And the purple connection as mentioned before is not present at all in the Jag Stang diagram, so is its presence in the Cobain Mustang diagram perhaps just redundant?

And just out of curiosity: does anyone know why the hot wire from the volume pot to the output jack is colored yellow (whereas all other hot wires in the diagram are white)? Does this represent anything special about that wire or connection? Perhaps the use of shielded wire? I had assumed that in a paint + foil / tape shielded guitar using black and white PVC insulated wire is just fine for all connections not coming directly from a pickup, right?

And one last question about shielding: I had already mentioned somewhere that I am planning to just put on some more layers of shielding paint to the factory applied shielding paint in the body cavities and have the paint spill over the edges to connect to the control plate and shielding foil / tape on the underside of the pickguard. Does anybody have any experience with doing that? Will that make a good connection, or should I opt for a physical wire connection between the paint and the control plate and foil / tape?

Any input will be much appreciated!

[OnnoP]

ok clearly I can't upload from my desktop, anyway, if anybody knows how to post an image that's not on an external website do let me know. If that's not possible, the link to the thread that has the Jag Stang and Cobain Mustang wiring diagrams is in my post, I hope that'll be enough for any member willing to help me out. My diagram is basically just the Cobain Mustang one, but with the pots changed to 500k ones, the capacitor to a .022 and the neck pickup is a Duncan Quarter Pound flat and the bridge a Duncan Hot Rails and I added an image from the Duncan diagrams that shows the color coding of their pickups (black = hot, green + bare = ground, white + red = soldered together and not connected). Your time and effort will be much appreciated!

[Futuron]

I can answer a few of those questions.

1. image posting: go to imgur, upload your photo/drawing to a 'new post' (you don't have to sign up or anything), then when it's done click on something like '... -> get share links' and copy the BBCode text option into your post here.

2. [pink] the wires/lack-of-wires to ground the switches: I think you've answered your own question, but my guess is that either there's shielding foil (and it's thus unnecessary) or it's been assumed that you'd connect those wires without needing a diagram to tell you to ground everything.

3. [purple] the different wiring of the Jagstang humbucker switch: I never knew this before, but it appears that the Jagstang is actually switched differently from that of the standard Mustang arrangement. Its bridge pickup is never wired 'backwards', so switching it left or right gives the same ON result. Normally, if both switches are in the same direction you are ON in-phase, and if they are opposite you are ON out-of-phase. But on that Jagstang diagram you are ON in-phase when the neck pickup is to the right, and ON out-of-phase when to the left, regardless of which ON direction the bridge switch is. The Cobain Mustang is wired normally. That's why the 2 diagrams are different there.