Star Grounding a Les Paul

[chemenger21]

Hi everyone,

I'm new to this forum, and to modifying my guitar generally. I recently changed the pickups on my epiphone les paul and I found that the guitar hums quite a bit now, more than it used to previously (even though it has humbuckers) and the noise goes away when I touch the strings. I'm thinking of applying the shielding/star-grounding method in the GuitarNuts site in the hope that this problem will go away - so my question is, do you think that this will fix the problem?

Also, although the instructions on the site seem pretty straightforward to adapt to a les paul, I'm still a bit confused as to whether or not I'll still have to make the back of my volume pot the ground point (since I'm not sure whether using the ring terminal on the pot shaft will work on a les paul as it does on a strat). So I was wondering, has anyone ever tried star grounding a les paul before? and if so could you post some pics or tips please? Thanks!

Finally, here is a picture of my guitar's control cavity, just in case I'm doing something obviously wrong...

[JohnH]

Welcome to GN2
A correctly wired LP with standard switching and Humbuckers should be fairly quiet, as yours was before. The main thing is that all the main wire wire runs are shielded, and all those shields are grounded. It looks like your pups have braided wires, so OK there. How about the wire runs from cavity to switch? There are three wires, being each pup to switch and switch to jack. All the shields should go to ground on the back of pots, plus at the switch, one of the shields should go to the body of the switch. Finally, is the tailpiece and strings grounded?

If you have all of that, then extra foil shielding could help further, the main thing is that it encloses the cavity, including back cover plate in contact with side wall foil lapped over, and grounded by contact with the pots.

John

[mr_sooty]

Sounds to me like somethings gone wrong during the pickup swap, and something's not grounded properly. I'm no expert, other guys here will help you out more, but I don't think star grounding and sheilding should be necessary on an LP. You just need to figure out where the mistake is and fix it. (edit: Johns post wasn't there ^ when I started typing. Listen to him!)

[sumgai]

chemmy,

Hi, and welcome to the NutzHouse! ;D


Long story short, yes, a guitar might/can/will buzz when the strings are not being touched by the player. That goes for any axe, whether it has single coils pups or humbuckers. The reason for that was pointed out by JohnH, above, in that the wire runs need to be shielded also, because they act like antennas for the EMI (electro-magnetic radiation) that causes hum.

Simple un-shielded wires are used in the great majority of guitars, but in many Gibsons, shielded wire is indeed the standard. This is why sooty said that you shouldn't have to do a QtB job on a LesPaul. I'd add to that ".... under ordinary conditions".

The reason for that is, if the axe was previously owned, it may have "suffered" at the hands of a hack. Or, in the case of your Epiphone, it's a well known fact that it does not copy a Gibson exactly - the matter of shielding (and more to the point, shielded wire) being one such concern.

From your picture, it looks to me like you just used the wires that were there (you didn't disturb what didn't need to be disturbed), so I'd first investigate those yellow wires running up to the switch, and back down to the jack. If they aren't shielded, as those from the pickup are shielded, then start by replacing them with the correct stuff.

Within the Les Paul's cavity itself, yes, it's always a good idea to shield, but is it truly necessary? No, probably not. But then again, your playing conditions may vary (considerably) from what I experience, so you'll have to be the judge of that word "necessary". This is a case where you look at the overall need (quiet guitar), and balance that against the overall cost (time and effort, cost of parts), and then make your decision. Going in stages, and testing the results at each step, is a good way to make sure you don't damage your credit card (too much). ;D

Star grounding is a slightly different story. The point of not using the back of a pot was to protect the player from possible electrocution, by preventing any exposed metal parts from possibly being touched during play. If you use plastic knobs, then the danger is considerably reduced, down to where I'd feel comfortable telling you that yes, the back of the pot is OK for a central, or star, grounding point. The ring washer/tab that was mentioned for a Strat is an option only where plastic knobs will be mounted. I think you'll find that the same thing could be done with your LP, the wood will and the tab on the washer will "reach an accomodation", if you will. But I'd just go the easy way, the back of the pot's shell, and be done with it. (Mind you, no Telecaster-style metal knobs!)

BTW, nice picture, and I have to admit, we haven't seen anything that clean on this forum in a long time. Don't worry, we'll fix that for you in a jiffy! ;D

HTH



sumgai

[chemenger21]

johnh said:

Welcome to GN2
A correctly wired LP with standard switching and Humbuckers should be fairly quiet, as yours was before. The main thing is that all the main wire wire runs are shielded, and all those shields are grounded. It looks like your pups have braided wires, so OK there. How about the wire runs from cavity to switch? There are three wires, being each pup to switch and switch to jack. All the shields should go to ground on the back of pots, plus at the switch, one of the shields should go to the body of the switch. Finally, is the tailpiece and strings grounded?

If you have all of that, then extra foil shielding could help further, the main thing is that it encloses the cavity, including back cover plate in contact with side wall foil lapped over, and grounded by contact with the pots.

John

The wire runs from cavity to switch aren't shielded, they're just normal wire. Didn't realise that those needed to be shielded...I thought that as long as they were well insulated it would be fine. I suppose that might explain the problem.

Also, should the braided wires on each of the pups have an outer insulator before they reach the control cavity (to prevent them from making contact with each other)? At the present they don't, although on my previous pickups they did. The bridge and strings are grounded (through the silvery wire coming into the cavity thats soldered to the top left pot).

[chemenger21]

Thanks to all for the replies! ;D

I think at this point the first step is definitely to replace the current yellow wires with shielded wire and see how that helps. Unfortunately I'm away from home (and my guitar) till next month so I'll only be able to do it then But will definitely get back to this thread and update on how it goes.

One other (probably silly) question I had, is there any special trick to getting solder to stick to the back of a pot shell? I use a 50W soldering iron, and I found it really hard...I had to apply lots of heat before it seemed that the solder was sticking to the pot and even then I was afraid to move it much in case it came off (not to mentioned scared I'd somehow ruin the pot)! Is this a case of needing a bigger iron?

[Sebster5696]

50W soldering iron!!!!!!!!!!
I'd melt the innards of my guitar with one of those. I recommend something much smaller such as a 25W iron. BTW you may have already wrecked your pots.

Seb

[JohnH]

Actually, my understanding is that a powerful iron is the best thing for soldering to pots. It heats the case up quickly and locally to melt the solder, without slow roasting it, hence causing less damage. Starting with a new pot is easier if you abrade the surface with sandpaper first. Im sure Sumgai will have wise experience to pass on on this.

Actually, personally, I prefer not to solder to the pot cases. I recently put new CTS pots into my LP, and they were grounded by attachmenr of their shafts to a ground plate, and I just soldered to the normal lugs for signal ground etc. If the guitar had not had a ground plate, I would have used ring tags around the pot shafts.

John

[sumgai]

John is correct, a hotter iron is almost mandatory for a larger surface, such as the back of a pot. This is because as you apply heat to a spot, it tends to radiate outwards from that contact point. If the heat radiates away from that point faster than you can feed it in, then you might as well be using a blow torch, because you are indeed overheating the surrounding area, and risking permanent damage to one or more components. A hotter iron overcomes this problem by quickly applying enough heat to melt the solder, before it can radiate outwards.

You can use a multi-temp iron, if the tip is large enough to actually deliver the heat to the contact point. Some of those irons, particularly the cheaper ones, are not capable of this, they have an 850° or 900° rating, but their tips aren't any good for more than about 750°. The more expensive units can do the job, with a broader surface tip, but then you can dial them back to a more reasonable temperature for the finer solder joints in your work.

I use an older Weller WTCP unit, about 40 watts. Too long on the joint and I burn the insulation, so control is the name of the game. (Well, that and some experience too, no doubt. ) But I can solder a pot-top ground joint in less than 15 seconds, so I've got probably a good middle-of-the-road solution.

Sand paper is a good way to go, on a new pot. No finer than 120 grit, and probably 100 is a bit better. 80 grit would probably work too, or just use what you've got on hand. Steel wool is too fine, it would take too long to get a properly prepared surface.


HTH



sumgai

[chemenger21]

Thanks sumgai, thats really useful. John, the ring tags sound like a very good idea, if I still have problems soldering to pots then I'll probably try that.