Grounding of a Jazzmaster

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lapsteel
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Grounding of a Jazzmaster

Post by lapsteel » Sun Dec 17, 2006 10:49 am

I have a '66 JM and everything works ok except for the hum in neck & bridge positions.

I've checked the continuity with a tester and it seems all hardware and internal shielding is properly grounded. If iI choose the both pickups combination, the guitar is very quiet, but if I select the bridge or neck, a background hum is always present.

It doesn't disappear when i touch the strings, and I've checked the wire below the bridge is well soldered to the internal shielding

When I first disassembled the guitar, it surprised me that the output jack doen't have the ground lug connected to anything, in fact it's perfectly clean, without any solder.

¿any tips?

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Re: Grounding of a Jazzmaster

Post by Jay » Sun Dec 17, 2006 11:06 am

The output jack isn't connected since it's considered grounded to the shielding itself (both the pickguard and tub).  I think the hum you are experiencing is likely normal.  The wide flat coils of a JM pickup are more prone to amplifying all kinds of noise from lighting and other sorts of electronic signals outside even moreso then a standard single.  The reason they're better in the middle position is they're reverse wound so that they hum cancel when combined.  Much like a humbucking pickup.  It's possible there is something wrong but all three of my guitars behave this way to some degree.  Hopefully others will chime in with advice as well.

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Re: Grounding of a Jazzmaster

Post by daydreamdelay » Sun Dec 17, 2006 11:34 am

yeah some noise is typical and there shouldn't be a ground to the input as Jay mentioned

do you have a ground wire going to the trem plate?

both of my 66's did and I know the one when I got it wasn't secured well and had fallen into the cavity, it was better once I set it back under the staple..  you might want to check that out

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Re: Grounding of a Jazzmaster

Post by lapsteel » Sun Dec 17, 2006 1:06 pm

Thanks!

The wire to de bridge is held with the staple and I've checked the continuity from the bridge to the output jack.

I had a japanese JM with SD JM-1 pickups a couple of years ago and it only had a slight hum that disappeared when i touched the strings. It didn't have all  those shielding inside, though.

I think it will probably be a ground loop or something similar.
Last edited by lapsteel on Sun Dec 17, 2006 4:21 pm, edited 1 time in total.

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Re: Grounding of a Jazzmaster

Post by jetset » Sun Dec 17, 2006 3:50 pm

What exactly causes a ground loop?  I'm wiring up a guitar at the moment and wanna know.  Should all of the sheilding be attached to the same ground as the pickups so you have one giant continuous ground of bridge/strings/trem/brass sheilding/pots/pickups.  Or should they be seperate?
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Re: Grounding of a Jazzmaster

Post by lapsteel » Mon Dec 25, 2006 2:16 pm

When I touch the polepieces, the buzz increases noticeably. It seems like the pickups were wound the wrong way, as if they were placed upside down (which is not the case).

I 've watched the bobins and solder joints very closely and they don't seem to have been rewound whatsoever.....

The guitar sound unbelievable, but that buzz really annoys me >:(

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Re: Grounding of a Jazzmaster

Post by Aug » Tue Dec 26, 2006 8:07 am

hmm...you may be experiencing 60-cycle hum, which is perfectly normal.  Also, the shielding should be grounded to the rest of the circuits...

when you get that hum, tilt the guitar forwards and backwards, and you should notice it gets quieter when perfectly vertical.

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Re: Grounding of a Jazzmaster

Post by lapsteel » Tue Dec 26, 2006 8:23 am

So is it normal that the buzz increases when I touch the polepieces?

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Re: Grounding of a Jazzmaster

Post by jetset » Tue Dec 26, 2006 8:27 am

Flourescent lights can cause huge hums in single coil guitars.  My basement practice space is terrible with 'em.
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Re: Grounding of a Jazzmaster

Post by Aug » Tue Dec 26, 2006 8:29 am

lapsteel wrote: So is it normal that the buzz increases when I touch the polepieces?
Yes...in fact, I just tested it out on my Jaguar...

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Re: Grounding of a Jazzmaster

Post by lapsteel » Tue Dec 26, 2006 8:35 am

Thanks! I'll sleep better tonight :D

For a while I was suspecting one of those dreadful franken-rewounds

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Re: Grounding of a Jazzmaster

Post by Sauerkraut » Tue Dec 26, 2006 8:51 am

My JM makes a lot of noise on it's own. It's all because of the pickguard (allparts) as it was dead quiet with the original (which has foil on it). I'm a bit too lazy to do something about the pickguard, I'm trying to figure out how to get the tremolo working nicely first. There's a grounding wire going to the tremolo cavity, like there's supposed to be, and now I'm wondering if I could decrease the hum by putting some aluminium foil in that cavity instead of under the pickguard. Does anyone know?

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Re: Grounding of a Jazzmaster

Post by Aug » Tue Dec 26, 2006 8:54 am

not sure if it'll really do anything, but I do prefer to use copper-shielding tape (www.stewmac.com) for under the pg and the very bottom of the cavities.  As for the ground wire to the tremolo, I always open that up (during a setup) and loop the wire around the nearest body screw.  This guarantees it'll never move/shift/whatever.

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Re: Grounding of a Jazzmaster

Post by Orang Goreng » Tue Dec 26, 2006 1:59 pm

Sauerkraut wrote: I'm wondering if I could decrease the hum by putting some aluminium foil in that cavity instead of under the pickguard. Does anyone know?
There isn't anything that can pick up hum in the tremolo cavity, so my guess would be "no".
In the land of the blind, the one-eyed man's a freak.

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Re: Grounding of a Jazzmaster

Post by Sauerkraut » Wed Dec 27, 2006 1:17 am

thanks, I'm really an idiot when technical matters are discussed.

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