Shielding/Star-grounding Problem

[ajk223]

Hello everyone. This is my first post on here. I came here via the guitarnuts.com forum link.

I've finished the instructions on the guitarnuts.com site for the shielding and star-grounding. I did every step exactly as specified except I left out the safety cap, simply because my local electronics store didn't have one and I don't play through vintage amps. Instead of the cap, there is just an insulated wire between the two ring terminals. Everything else is exact.

Here are my problems since completing this:

1. When I touch the string(s), there is an audible 'crackle' coming through. It's only heard when my finger initially touches the string. Also, the hum on positions 1, 3 and 5 seems louder than before! There definitely seems to be some staticy-sounding noise that seems to come and go as well.

2. I noticed if I touch one of the magnets on the neck pickup, there is a staticy-sounding buzz that continues as long as I hold my finger there -- is this normal?

3. The third and weirdest thing is that the middle+bridge position on the switch is JUST the middle pickup now and there is an audible 'pop' sound when going from the middle position to the middle+bridge position on the switch. The thing is, I didn't touch ANY of the hot wires or switch, whatsoever.

I've checked the continuity between the trem claw and the cavity, numerous random points in the cavities, and numerous points on the pickguard foil and all is OK.

I've also checked for continuity from the solder joints on the pickups to the pickguard shield, and all ground points are indeed continuous to the pickguard (via the ring terminal), and theoretically then to the cavity and eventually the trem claw.

My amp, cables and electrical outlet are all OK. I didn't accidentally reverse the wires on the jack, either (checked that).

What is this a sign of? It's driving me mad. Could something possibly be touching the cavity shield? I insulated the ground terminal with electrical tape. The lead from the tone cap is also insulated.

Could it be possible that the switch lugs are touching the cavity shield? I didn't think I'd have to worry about that. Could the switch be bad and that's what's causing these problems? Bad pots? Help!

Any ideas or suggestions will be greatly appreciated!

[newey]

ajk233-

Hello and welcome!

This sounds like it may be more than one problem. You may have to stick with us for awhile, but we'll get this sorted.

Your problem #3, as well as the increased noise at 1,3 and 5, might well be due to the switch touching your shielding. You can test this with the guard wired up but detached, a screwdriver test will tell you whether you've got both mid and bridge pups. If you do, your switch is making contact in there somewhere. You can use electrical tape over the shielding at the critical areas to insulate the switch contacts.

I've also checked for continuity from the solder joints on the pickups to the pickguard shield,

I'm not sure to what this refers.

[gitpiddler]

Welcome alk223, I got here the same way.

One important step on my 1 pickup, one vol. pot axes that made the most improvement was cutting the tab between the signal return (grnd) term. on the pot and the pot casing. No shielding yet, the Tele has that metal plate which grounds everything. The Stratoid needed a ground wire from jack to vol. pot case and bridge. THAT was my biggest source for noise on both, and I'm forever grateful to John for his website.

I assume the bridge pup (HB or single-coil?) works without the middle. Sounds maybe like a tab or wire touching the shield also.

Good luck, keep us posted.

[ajk223]

newey & gitpiddler -- Thanks for the super-quick replies!

Here's what I got so far:

Last night I tested the switch. Basically, I tested for continuity from the hot solder joint on each pickup (where the hot pickup wires connect to the pickup) to the input lug on the volume pot in all 5 different switch positions. With the pickguard detached from the body, the switch functions exactly as it should:

1 - bridge
2 - bridge/mid
3 - mid
4 - mid/neck
5 - neck

Unfortunately with my crazy schedule during the week, this is all I had time to check last night after work. I only had about 20 minutes at the house to get a shower and check the switch, and I may not have time to get into it again 'til Friday.

So, my switch is OK. I'm starting to think it's definitely the switch touching the shielding, therefore transferring the ground noise to hot. I also forgot to mention that I was getting hum from position 2 on the switch, which didn't happen before and shouldn't happen AT ALL considering the middle pickup is reverse-wound.

The shielding touching the hot signal somewhere would also explain me hearing myself touch the strings through the amp -- I touch the grounded string(s), that noise goes to ground which is possibly going to hot, and so I hear it through the amp. It would also explain why I get buzzing when I physically touch the pickup magnet -- normally, if you touch the pickup magnet with your finger, any contact noise would go to ground, wouldn't it? In my case, it seems like it is indeed going to ground, but the ground itself is going through the hot as well.

newey -- What I meant by "I've also checked for continuity from the solder joints on the pickups to the pickguard shield" was this: there are 2 soldrer joints where the pickup wires connect to the pickup, one hot and one ground. I checked continuity from the ground joints of each pickup to the pickguard to make sure they were indeed connected to ground.

gitpiddler -- While doing the star-grounding process, I desoldered the 3rd lug of the volume pot from it's own shell, since it's now grounded by the foil.

Sorry if any of my terminology or explanations are off. I'm still somewhat new to some of this stuff.

So what do you guys think? It's starting to seem that there is really only possible cause for this: some part of the shielding is touching part of the audio circuit (the switch lugs?), therefore sending ground noise(s) to hot.

That is possible, right? Is that what would actually happen if the switch was touching the shielding? It would send ground noise to my hot signal, and through the amp?

Thanks again guys... like I said, I may not be able to work on this 'til Friday now, but I will surely keep you posted. Any more ideas and suggestions are welcomed as well, but I think you guys may have nailed it already.

[ChrisK]

It sounds to me that you have (a) circuit continuity issues(s).

Since you apparently have a digital multi-meter (i.e. "checked the continuity"), could you take some resistance readings at the output jack?

Set the volume pot to "10" and set the tone controls to "10".

Plug a guitar cable into the output jack and measure at the unplugged other end.

Set the meter to the 20 K Ohm range. Measure the resistance for each position of the 5-way selector and post the readings accurate to at least 3 and preferably 4 digits for all 5 positions. This will check for proper pickup selection.

In each position, vary both tone pots independently to see if there is a lasting change to the reading (i.e. it settles to a new value). This will check for tone circuit wiring errors or shorted components.

Also, for each of the 5 positions, set the volume pot to "5" and also post that value. This will check for volume pot functionality and connectivity.

It would send ground noise to my hot signal,

If there's "ground noise", it's inherently "in your hot signal" anyway since this is the same circuit loop (to the amp).

I never depend on the shielding (in-cavity or pick guard) for connectivity, I always run wires from pot shell to pot shell (redundancy is). This includes Tele control plates as well.

A shield is a shield, and not a conductor. It may well be conductive (which is a good thing), but it is not a signal conductor.

normally, if you touch the pickup magnet with your finger, any contact noise would go to ground, wouldn't it?

No. In a Strat, the individual magnets are not connected to anything.

[ajk223]

ChrisK --

Thanks for looking into my problem! Unfortunately, I probably won't get time to get you those readings until Friday or Saturday.

I am very sure that selector switch is indeed functioning properly and sending the correct pickup combinations to the tone pots, volume pot and eventually to the output jack.

The volume knob works as it always has. The guitar is just as loud as always and is also dead quiet when the volume is all the way down.

The neck tone knob functions as it always has, and the 2nd tone knob (which is a no-load Delta Tone wired to control both the middle and bridge pickups) seems to function perfectly as well.

I know these are just auditory observations, but it's all I can fill you in on until Friday or Saturday.

Again, much thanks. I'll be back!

[ChrisK]

3. The third and weirdest thing is that the middle+bridge position on the switch is JUST the middle pickup now and there is an audible 'pop' sound when going from the middle position to the middle+bridge position on the switch. The thing is, I didn't touch ANY of the hot wires or switch, whatsoever.

The "pop" sounds like capacitive coupling or switched capacitors afoot. If only the middle pickup is selected in the middle+bridge position on the switch, the wiring ain't right.

If you didn't touch ANY of the hot wires or switch, what DID you touch?

Another engineer said to me many years ago "the product has to be working right, I didn't do anything except change the software."


Also, it may be that a microscopic black hole was trapped in the control cavity when you put the pick guard back on, but this is somewhat unlikely.......


Occam's razor.

[ajk223]

ChrisK --

Here's the thing: While the pickguard is installed, there's no difference between the 2nd (bridge/middle) and 3rd position (middle) on the switch, and I get that audible pop/click sound when going from 3 to 2. So it's not working properly while installed in the guitar, but...

I tested the switch while the pickguard is DETACHED from the guitar, and it switches perfectly. I did this by setting the switch to position 1 and testing continuity between the input lug on the volume pot and each of the hot pickup leads. In position 1, I only get the bridge. In position 2, I get the bridge and middle. In position 3, I only get the middle, etc, etc. I'm unsure of how to use the multimeter to check for the popping sound between 3 and 2.

I didn't touch any hot wires, and there's only one tone cap, which I didn't touch either. The only thing I did was shield the cavities and pickguard and star-ground all the ground wires. Basically, the following link is what I did, minus adding the safety cap, because I didn't have one.



The link above is actually how I got to this forum.

I also sincerely apologize for not being able to try any of these suggestions until later this week. I didn't know the people on this forum were going to respond so quickly!

[ChrisK]

Well, it certainly seems like there is some shorting going on once the pick guard is placed back into the body. You could remove most of the pick guard mounting screws except for the ones near the neck, plug the guitar in and press down on the pick guard to see where the fault is occurring.

The reason for measuring the resistance is to see what is shorting (or opening) once the pick guard is mounted.

Also, can you post some digital pics of the pick guard wiring?

(Make sure that they're in focus, please.)

It may be that something is indeed opening once mounted.

[ajk223]

ChrisK --

I'll try what you said about pressing down on the pickguard. If I can't figure it out by doing that, I will surely get some pics as well as some resistance readings for you.

Thanks so much for your time and help!

[ashcatlt]

Feb 10, 2009 18:51:27 GMT -5 ajk223 said:

2. I noticed if I touch one of the magnets on the neck pickup, there is a staticy-sounding buzz that continues as long as I hold my finger there -- is this normal?

Today I came up with a theory on this phenomenon. The question comes up every once in a while, and never really gets adressed. I think that's because there's usually some other problems with the build.

First, I assume by "touch one of the magnets" you're actually talking about the metal pole piece, yes? I found today that if I touched the metal rails on my strat's pickups I get a significant buzzing. With humbuckers and shielding, it's normally a pretty quiet guitar and this was very noticeable. The buzz also comes from touching metal screws holding it into the pickgaurd. These have no reliable conductive path to anything!

I also found that this buzz goes away completely if I touch the strings at the same time. Try that little experiment, just for fun. My idea on this is that the metal pole peice (and screw) acts as a sort of antenna. It perhaps focuses and definitely conducts the EM noise from your body very much closer to the coils, where it is induced into the signal path. I'd imagine that touching the coil itself would have a similar effect.

The solution to this one seems simple. Don't touch the pole pieces.

[ajk223]

OK guys, I finally got around to work on my guitar. It's fixed. Here are my results, conclusions, solutions, etc. --

Problem #1, concerning the crackle when I touch the strings and there generally being more overall noise: Apparently (at least in my case anyway), the capacitor that is used to alleviate electrical shock is NECESSARY in this wiring scheme, as it isolates the shield ground from the signal ground (or at least I think that's what it does, anyway?). Without this, all shielding is directly continuous to all of the other ground wires (is that a ground loop?). There is a part in the instructions that says you can "omit the capacitor entirely", but when I did just that, I was left with more noise and the crackle when I touched the strings. My reasoning for why this works how it does may be incorrect, but I do know that installing the capacitor helped immensely with this problem. The guitar is now VERY quiet as far as hum and buzz goes: much quieter than stock (almost completely silent in my house!) and definitely MUCH quieter than without that cap!

Problem #2, concerning buzz when I touch the pickup poles: Still happens, but I think this is fairly normal and I just never noticed it before. I'm completely with ashcatlt's theory on this. I never touch the poles anyway (apparently I do when I'm worried about other noises the guitar is making :

Problem #3, concerning me not getting the position 2 combination to work properly: This is perhaps the most interesting and frustrating part of all. I later realized that not only was position 2 not working properly, but every position except for position 5 (neck) sounded 'off' (I know -- I should have realized this sooner and told you guys... sorry!). It turns out that the solder lug on the ring terminal that I installed over the 2nd tone pot shaft was pushing up on the lugs of the pot while it was mounted and somehow shorting it out. Is that ridiculous or what? Maybe it's not, but to me it was. So I moved the ring terminal to the 1st tone pot and installed it so that the lug end was on the other side of the pot (NOT where the pot lugs are). Problem solved.

No connections on the switch were touching the shielding, like I was starting to suspect.

Just figured I'd let you guys know of my findings. So yeah, thanks a ton newey, gitpiddler, ChrisK & ashcatlt. Thanks for taking the time to help me out!

Feel free to post any comments about the results. I'll be around.

Take care,
-Tony K.

[newey]

ajk-

Glad you got it working!

Apparently (at least in my case anyway), the capacitor that is used to alleviate electrical shock is NECESSARY in this wiring scheme, as it isolates the shield ground from the signal ground (or at least I think that's what it does, anyway?). Without this, all shielding is directly continuous to all of the other ground wires (is that a ground loop?). There is a part in the instructions that says you can "omit the capacitor entirely", but when I did just that, I was left with more noise and the crackle when I touched the strings

I can't really comment on "your case" since I don't know how you have this wired. If it's working, that's the main thing. But the cap does not isolate the shield grounds from the signal grounds.

When omitting the cap, it is replaced with a wire. You did, I assume, run a wire where the cap would have been when you omitted it?

[ajk223]

newey --

Now it's wired EXACTLY like this:


Before, instead of ring terminal -> cap -> ring terminal, it was just ring terminal -> insulated wire -> ring terminal.

When wired without the cap, there was continuity (zero resistance) between say, the shielding and one of the pickup ground wires. With the cap installed, there is no continuity between those 2 things, yet both are still wired to ground.

Like I said, my reasoning could be completely incorrect. All I know is that with the cap installed, the noise is gone. Installing that cap was the very first thing I did after I noticed the guitar was noisier, and I did that solely so I could properly troubleshoot the guitar with the multimeter following this guide:


Some of the problems on that guide were a result of the isolation capacitor (that's what he calls it) either being not wired correctly or bad. So I figured if I didn't have it installed, I wouldn't be able to do those particular tests.

Oh well. Like you said, the main thing is that it's working properly now! ;D

[ashcatlt]

The isolation cap (like all capacitors) exhibits a higher amount of resistance to lower frequency signals. DC voltage = 0 Hz, an extremely low frequency, and is essentially blocked by that cap. Your meter tests continuity/resistance by running a DC voltage through the circuit. So, you're both right.

I suspect that in installing the capacitor you may have somehow improved the overall shield>ground connection. That is, you accidentally fixed the overall noise problem.

The clicking sound may have come from a DC offset or fairly high energy low frequency noise which was either changed or eliminated when you touched the strings. In this case, installing the cap would mean that touching the strings doesn't change that part of the signal. It's still there but too low to be audible.

[musicmanjp6]

I'm new to the forum and just started shielding my guitar. I too cannot find the appropriate capacitor to use. I'm wondering why the wire running from the tone pot to the terminal is so important and if the capicitor is really that crucial to the noise performance of my guitar.

I have the omitted capcitor lead and one other lead to solder to the terminal ring and then i'll be ready to wire up the input jack and start testing. Hopefully it cures my noisy guitar!

Also, will the shielding improve my guitar's tone? That would be a very cool added bonus!

[newey]

mmjp6-

Hello and Welcome!

Shielding won't affect your tone for better or worse. There may be a subjective effect, however, as with less noise you may be able to play at higher levels without noise. You may, up to now, have been backing off on the levels due to noise, and when that is removed, it seems somehow "better" even when turned up more.

The 400V safety capacitor in the original Guitarnuts scheme is there for protection from potentially lethal voltages. It does not contribute in any way to noise reduction. It can be eliminated by simply replacing it with a length of wire in the diagram.

The safety cap is important, however, if you use a tube amp, or if you will ever use one in the future.

[musicmanjp6]

I've used tube amps for years and never had a problem. Most guitars do not have this safety cap if i'm not mistaken. If I could find one i'd put it in there!!!

Thanks for the reply. I'll let you know if I run into troubles when testing...

[newey]

I've used tube amps for years and never had a problem

That's the same thing all the guys who got electrocuted said.

Most guitars do not have this safety cap if i'm not mistaken

Yes, which is why people occasionally get electrocuted.

If I could find one i'd put it in there!!!

Try Parts Express at this link

The risk of catastrophic failure of your tube amp is small, but is nonetheless real. The safety cap is like a fire extinguisher in your kitchen- you may never need it, but it's cheap insurance.

If I used a tube amp- I don't at present- I would either put the safety cap in all my guitars, or throw away all my guitar cords and solve the problem by going wireless.

[musicmanjp6]

What i'll probably do is proceed without the cap for now and just see if the noise subsides. In the meantime i'll keep trying to find one locally or find a reason to order more from Parts Express to make the best of the shipping costs.

I'm gonna try to work on the guitar more tonight. Is it OK to solder the tremolo ground to the copper foil rather than use a wood screw and washer?

[newey]

Is it OK to solder the tremolo ground to the copper foil rather than use a wood screw and washer?

That's fine so long as you can get a good connection to the copper foil. The instructions cover using aluminum foil and shielding paint for shielding, in addition to the copper foil method, and with those other methods you can't solder it on, so the screw and lug method is used.