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FDP Forum / The 'Pup' Tent / Hum/Grounding Diagnosis

Next 20 Messages  


I ain't gonna worry my life anymore....
Feb 7th, 2007 04:06 PM   Edit   Profile   Print Topic   Search Topic

Have just had a set of VN's installed in my 2001 MIM Strat, by a qualified dealer/technician. Sounded fine in a noisy shop, but once home, I noticed a hum/buzz when I'm not touching strings or bridge. Suspecting grounding issues, back to shop for them to check. One week later, they're still stumped, having replaced jacks, selector switch, complete rewire,
and still same problem. Im now tempted to open her up and try to find the prob myself, any procedures
or order of operations on isolating grounding issues folks?

Contributing Member


Feb 7th, 2007 07:11 PM   Edit   Profile   Print Topic   Search Topic

What pickups did the VN's replace? Did the guitar exhibit this symptom with the prior pickups? My suspicion is that it probably behaved in a similar manner with the prior pickups, but the ground buzz was being masked or overwhelmed by the hum and other noise the pickups were receiving.

In my experience, even hum-canceling pickups will do just what you describe when there the guitar has inadequate shielding. Many players have noise-free pickups installed expecting them to solve all noise problems, and then find themselves disappointed in the results when shielding is ignored, only to come to the conclusion that hum-free pups just aren't any good.

Do yourself a favor: make sure that the guitar body cavity is correctly shielded and that all redundant ground loops are removed. The noise you describe will go away. Guaranteed.



I ain't gonna worry my life anymore....
Feb 7th, 2007 07:25 PM   Edit   Profile   Print Topic   Search Topic

Thanks Vandenberg, the previous pickups were EMG-SA's, and the guitar exhibited no such problems. I wish I shared your confidence, but nevertheless,
I will pull her to bits tonight.

p.s. Off topic, I know, but why is the gender of guitars always female? Is it something to do with
the names we call them when they dont work properly?



Feb 7th, 2007 09:06 PM   Edit   Profile   Print Topic   Search Topic

Don't know for sure, but most EMGs are active, so 60 cycle hum is never an issue there. Being a MIM, it probably has no shielding paint like newer MIA fenders.

While single coil PUPs are the biggest offender, all pots, wires, and anything else not connected and grounded to a completely shielded cavity can generate hum. Use copper tape soldered together or shielding paint with a lug connected to ground everywhere to minimize, if not eliminate hum.

And guitars, boats and plenty of other things all seem female, because you love them even when they make you want to hate them :)


Land Of 1000 Dances

Feb 7th, 2007 09:56 PM   Edit   Profile   Print Topic   Search Topic

"Being a MIM, it probably has no shielding paint like newer MIA fenders"

There are MIM Strats that have shielding paint and have had it for many years.I have one made in 1997 and it definitely has it.If you look in the control cavity and there's a wire with a lug on the end which is screwed into the body,it's shielded.The wire is the ground for the shielding paint.Sometimes you won't see the flat black shielding paint because they spray the finish over it.

Contributing Member


what you think is true, you're right!
Feb 8th, 2007 05:29 AM   Edit   Profile   Print Topic   Search Topic

spud1950: I noticed on my olympic white MIM '70s Stratocaster that the control cavity has around a 2 x 2 inch patch that is clear poly with a serial number sticker under it and no sign of sheilding paint and it hums like a mofo but the pickup tone sounds awesome. I'm thinking maybe I need one of those Stew-Mac shielding kits. I can't remember if it had the lug but the fact that I can see that 2 inches square of clear wood, wouldn't that indicate that it's not sheilded? Can you do more harm than good to sheild a guitar that's already sheilded? I'll probably go with the tape because if I notice it adversely affecting the tone I can take it back out, whereas the shielding paint is permanent. Incidentally, when I watched a video of them taking Eric Clapton's Blackie Strat apart, it appeared he had some kind of grey sheilding paint all around the pickup and control cavities.

poida3934: Stevie Ray's favorite guitar's name was "Lenny" and Eric's was "Blackie" and Jimi's favorite black Strat that he used in Band of Gypsys was named "Black Beauty" after a certain type of speed drug he liked. So I guess only wimpy guitar players use female names. haha



Feb 8th, 2007 07:26 AM   Edit   Profile   Print Topic   Search Topic

You can only increase the hum blocking power of a guitar by putting shielding on top of more shielding. I have always had great results with the copper foil tape and an exacto knife. I always just drop a helthy blob of solder in one of the corners of the control pocket (somewhere where there is no possibility of the controls comming in contact with it) and solder the ground wire directly to the copper tape. It makes a super solid electrical (and mechanical) connection. Also, use an ohm-meter to check continuity between the different pieces of tape. Some even put solder to bridge the electrical connection between the pieces of tape, but I have not found this necessary with the tape from Stew-Mac. Tape up the entire control cavity, pickup cavities and channels in between. Cover the bottom side of the pickguard over the same areas. No need to solder to the tape on the PG as it is grounded by the metal control pots. If your guitar doesn't sound right or does funky stuff when you switch between 5-way switch settings, something is shorting out to the shielding. Just find out what's touching and put a piece of electrical tape over the shielding in that area and you will be good to go. This will not have a negative effect on the shielding, it will just keep it from connecting ground to something that should not be grounded.

Contributing Member


what you think is true, you're right!
Feb 8th, 2007 12:42 PM   Edit   Profile   Print Topic   Search Topic

guitarphred2: Great info! Thanks! A few questions though.

1. What is the healthy blob of solder for? Are you attaching the copper foil to that or to the ground wire as you mentioned you also solder the ground wire to the copper foil. Isn't that all supposed to be attached to the wire that's soldered to the tremolo claw?

2. Are you cutting the tape into the wood and making slices into the paint around the edges as you edge off the excess copper foil?

3. Can this be all undone if the results are not desirable?

4. When you say checking for continuity with an Ohm meter what type of reading are you looking for and what setting do you have the meter at? 20k Ohms etc?




Feb 8th, 2007 02:27 PM   Edit   Profile   Print Topic   Search Topic

Not a problem, happy to share what little I know. All good questions to be asking.
1) Helthy blob=about the size of the end of an eraser or more. About how much you would plop down on the back side of a pot to run a ground wire to it. This will make it easy to solder the ground wire to the shield and will hold it good when you accidentally tug on the wire when trying to put the pickguard in place or the next time you take it off to change out a cap on the tone pot, etc. Put the solder blob in the floor/wall corner in the control cavity. I usually put it on the wall toward the neck / in the direction of the pickups. Both (one on each) on the wires. The one on the spring claw grounds the strings, the one on the foil grounds (activates) the shielding. Run the wire from the shield to ground, typically on the back side of the volume pot.
2) I start by completely covering "floor" of the cavities. Use the exacto knife to trim any extra tape to where it only covers the floor. Next, do the same for the walls, allowing about a 1/16" to 1/8" overlap over the tape on the floor. Trim the top rim flush with the surfact of the top of the body with a sawing motion from the copper side of the tape. This will give you a clean cut all the way around. It is important to not go above the top surface with the tape a it will prevent the pickguard from sitting down flat on the guitar. You should never need to cut any existing paint during this process. The key is patience. Minimize how many layers of tape you stack up, especially in the control cavity. It will not harm it's ability to shield, it just adds to the risk of accidentally shorting something out to the grounded shield. Thoroughly press and smooth all of the tape down to ensure good tape-to-tape contact.
3) Absolutely, it can all come out just like taking up masking tape. It's definitely worth working out any issues (like accidentally grounding the legs of a pot) to get the benefits of greatly reducing the noise.
4) Set the meter to the lowest setting, what you are looking for is 0 ohms from any point to any point on the foil. Move the two probes around randomly all over the surface of the taped area to ensure everything is 0 ohms. Any scrap of tape that does not read 0 ohm (or at least 2-3 ohms or less), first try re-stabbing the probe into the tape to ensure good contact to the tape, then press the tape down some more in that area to ensure a good connection to the surrounding tape.


Willowbrook, IL

Only the poor craftsman blames his tools
Feb 8th, 2007 03:09 PM   Edit   Profile   Print Topic   Search Topic

All guitars humbucking, active,single coil etc., hum when you turn the volume up and are in a noisy room if you are not touching strings or bridge. When you are home test your guitar that is currently doing it. Then take any other guitar and check to see if it does the same thing. It will. They all do. You are the ground!!!!!!!!!!

Contributing Member


what you think is true, you're right!
Feb 8th, 2007 04:06 PM   Edit   Profile   Print Topic   Search Topic

guitarphred2: So that blob goes under the tape or on top of it before sticking the wire into it? Do you have any pics of a finished one? I thouht I read somewhere that you had to put an overlap om the top of the cavity so it would come into contact with the shielding on the pickguard. See the pics on this page

Shielding a Tele

(This message was last edited by yes9310 at 04:10 PM, Feb 8th, 2007)


Land Of 1000 Dances

Feb 8th, 2007 05:02 PM   Edit   Profile   Print Topic   Search Topic

Here's a really nice shielding job with great photos and directions.Click on the photos to enlarge them.Very clear and easy to understand.

Strat Shielding

(This message was last edited by spud1950 at 05:04 PM, Feb 8th, 2007)



Feb 8th, 2007 05:09 PM   Edit   Profile   Print Topic   Search Topic

I just pulled one of mine apart and saw that I did let it overlap over the top by about 1/16". Doing so does not hurt anything, but the PG is already grounded by the pots being installed. The blob of solder goes on top of the installed tape. Just solder it down to the tape itself. Don't leave the iron on the tape for more than a second as it will easily burn through. The good thing is that the tape requires almost no heat to get the solder to wet (stick to it). spud1950's link is an excellent example of a shielding job well done. Reference the pics there to see what the finished product should look like.



I ain't gonna worry my life anymore....
Feb 8th, 2007 06:07 PM   Edit   Profile   Print Topic   Search Topic

Thank you all for your input, pardon the pun.
I now understand I am a wimpy guitar player who
doesn't know what he is listening to! As a result,
I have decided to nickname my guitar Brutus, crank up the gain, and pretend "noise" is the sound I'm trying to achieve! But seriously, thanks for all the advice and references provided, I will report back when I
locate the gremlin. And just as an aside, my Greg Bennett Avion, and even my daughters SX strat copy,
don't display such symptoms in the same room through the same amp. Thanks again all.....


Land Of 1000 Dances

Feb 8th, 2007 07:13 PM   Edit   Profile   Print Topic   Search Topic

Another factor as far as guitar noise caused by ground problems is how well the wiring in the building that you're playing in is grounded.In my apartment I get some buzz coming out of the amp speaker.When I play at my friends house,who recently had an electrician redo the the ground in his house wiring,the thing is absolutely silent.A lot of people never consider this.



Feb 8th, 2007 09:04 PM   Edit   Profile   Print Topic   Search Topic

Definitely! Same goes for the clubs. You never know the quality of their AC circuits until you plug in and crank up to show volume.


Land Of 1000 Dances

Feb 8th, 2007 09:18 PM   Edit   Profile   Print Topic   Search Topic

It's something people really overlook.If the wall socket has a poor ground,the ground to the amp will be poor.The guitar,getting it's source of ground from the amp, will then itself be poorly grounded.Makes sense to me.



Feb 8th, 2007 09:25 PM   Edit   Profile   Print Topic   Search Topic

Sometimes VN pickups come with 1meg pots. If this is your case and those 1meg pots were installed ,there will be no circuit load and that is likely the cause of the noise. Shielding is a good thing to do, but it is NOT the cause of your problem.
If you are checking wiring, make sure there is a ground circuit to the strings. Check it with a meter.

Contributing Member

Asheboro, NC

but my heart's still in Texas
Feb 8th, 2007 11:04 PM   Edit   Profile   Print Topic   Search Topic

Sidebar: SRV's "Lenny" was named for his wife Lenora. And it wasn't his favorite -- the guitar he played most (and is most closely associated with him) was the beat-up sunburst he called "First Wife" or "#1". "Main" was his Hamiltone (the one with his name inlaid on the fretboard) -- in some interviews he gave the impression it was his favorite.

His other guitars had names like "Red", "Scotch", "Yellow", and "Butter".

He did have a guitar called "Charley" -- that was the white one with lipstick pickups, which was a gift from his friend Charley Wirz (of "Charley's Guitar Shop" in Dallas).


B.B King has "Lucille", Albert King had "Lucy", Roy Buchanan had "Nancy". Most guys who name their guitars go for either feminine names or descriptive names.

Contributing Member


what you think is true, you're right!
Feb 9th, 2007 06:14 AM   Edit   Profile   Print Topic   Search Topic

guitarphred2: Thanks for the clarification and all the great tips!

mrfix: How can you test with a meter if there is a ground circuit to the strings? On my new MIM 70s Strat I noticed a slight buzz until I touch the strings that I don't notice with my Am Strats. When I see that small patch of aluminum foil just covering the control area, does Fender feel that's all that's needed?

strayedstrater: Interesting that most of Stevie's guitars were masculine named. Doesn't look like he had any named "Pink". Check out a masterbuilt (by Fender's Chris Flemming) one of a kind copy of Roy's "Nancy" at Barry Levenson's site.

Roy Buchanan's "Nancy"

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