Jaguar: Hum with Both Pickups Off?

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Danley
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Jaguar: Hum with Both Pickups Off?

Post by Danley » Tue Jun 27, 2017 6:30 am

I rewired my MIJ Jaguar long ago, and don't know if it just started doing this or it was always like this... But is it normal to experience hum (like, ungrounded guitar noise) when both pickups are off? Any pickup and knob combination does not have the hum, except the "kill" position. At a glance my schematic matches this:

Would both off actually generate ground hum with this schematic? Or is there anything specific I should look for or a fix for this? All my brass shielding is grounded, plates, pots are grounded etc...

I got a bit practical, hooked a multimeter to the jack tip and checked for continuity to ground. With both pickups switched off, there is no continuity. But per the schematic... Should there even be? Unless I'm reading it incorrectly, I think no? Both pickups switched to the "off" position doesn't ever loop back to ground, it seems... Wouldn't that be a cause for hum? I can kill the hum by turning the volume all the way down with both pickups off if that matters, I guess that only means my knob is grounded.

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molwam
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Re: Jaguar: Hum with Both Pickups Off?

Post by molwam » Sat Jul 08, 2017 1:21 am

According to this schematic, the signal path is not switched to ground, when all pickups are off. I think I shoudn't be humming, at least my bass vi doesn't and its schematic is pretty similar to yours. Can you measure from the tip of the input jack to its sleeve with both pickups off and volume up all the way? It should read 1M, so that the signal path has at least some connection to ground via the volume pot. That would be the first thing, that came to my mind. But since you said that the hum is gone, when volume is turned down, I'm not so confident, that there is something wrong with the volume pot. But It's better to check this ;)

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Re: Jaguar: Hum with Both Pickups Off?

Post by soulgolem » Sat Nov 02, 2019 5:49 am

did you figure it out ? i’m having the same problem with my mustang.

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Re: Jaguar: Hum with Both Pickups Off?

Post by Danley » Sat Nov 02, 2019 7:17 am

I have two Mustangs and they’re fine - no hum with both pickups switched off, and I wired using the instructions I archived from Shortscale.org . I never bothered to try and fix or track down any possible ground issue on the Jaguar, in practical use it didn’t bother me to the degree to obsess over it but maybe I’ll take a look at it again now.
King Buzzo: I love when people come up to me and say “Your guitar sound was better on Stoner Witch, when you used a Les Paul. “...I used a Fender Mustang reissue on that, dumbass!

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Re: Jaguar: Hum with Both Pickups Off?

Post by timtam » Sat Nov 02, 2019 6:00 pm

There are two extant variants for kill switches: one that simply breaks the connection of the hot to the output jack (leaving an open circuit), and the other that shorts the output jack hot to ground. You want the second.
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Re: Jaguar: Hum with Both Pickups Off?

Post by JohninJapan » Sun Nov 17, 2019 4:23 am

Hi there, not sure if anyone has already posted the solution to your question but I have a quick fix for you if not.

If you pop the pick guard off your Japanese Jaguar and don’t see copper shielding plates but instead see black shielding paint then it’s pretty straightforward. Earlier MIJ (first version MIJs) had lots of copper shielding and seem to be largely free from the grounding issues of newer models.

Remove the screws from the lower control plate (the one with the input jack) and flip it over taking care not to break any of the connections.

Cut a length of wire long enough to stretch from the master volume pot to the space in front of the two pickups and thread it through the small hole in the body.

Solder one end of the wire to the volume pot and solder the other either directly to the screw or as I prefer to do a small metal bracket and screw it into the paint.

My CIJ Jag was driving me insane with the grounding noise before I did this and after installing this extra wire it’s absolutely dead silent now. This wire isn’t shown on any of the fender wiring diagrams so I’m assuming this problem will be plaguing a pretty large number of folks out there. I’ve done the exact same fix on a number of friends Japanese Jazzmasters and Jaguars and it’s resolved all of the problems with them.

Hope this helps!

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Re: Jaguar: Hum with Both Pickups Off?

Post by timtam » Sun Nov 17, 2019 5:02 pm

JohninJapan wrote:
Sun Nov 17, 2019 4:23 am
Hi there, not sure if anyone has already posted the solution to your question but I have a quick fix for you if not.

If you pop the pick guard off your Japanese Jaguar and don’t see copper shielding plates but instead see black shielding paint then it’s pretty straightforward. Earlier MIJ (first version MIJs) had lots of copper shielding and seem to be largely free from the grounding issues of newer models.

Remove the screws from the lower control plate (the one with the input jack) and flip it over taking care not to break any of the connections.

Cut a length of wire long enough to stretch from the master volume pot to the space in front of the two pickups and thread it through the small hole in the body.

Solder one end of the wire to the volume pot and solder the other either directly to the screw or as I prefer to do a small metal bracket and screw it into the paint.

My CIJ Jag was driving me insane with the grounding noise before I did this and after installing this extra wire it’s absolutely dead silent now. This wire isn’t shown on any of the fender wiring diagrams so I’m assuming this problem will be plaguing a pretty large number of folks out there. I’ve done the exact same fix on a number of friends Japanese Jazzmasters and Jaguars and it’s resolved all of the problems with them.

Hope this helps!
Interesting re MIJs. While vintage-accurate JMs typically have grounded shielding plates, Squiers commonly have paint-shielded cavities with wires linking each cavity to ground (see below). This is presumably because shielding paint does not typically have zero-ohms continuity from point to point, like with copper foil or each shielding plate. Shielding paint is commonly specified as 50 ohms/10mm2 for example, so there will be a small resistance from point to point across the paint. The question is whether this small resistance really matters as far as shielding performance is concerned; I have not previously seen any testing to say one way or the other. Fender either do know it does matter, or just hedged their bets when they found the non-zero resistance of their paint by specifying ground wires for each cavity instead of just the main cavity (with continuous paint between cavities) on the Squiers, so at least the centre of each cavity is at zero ohms to ground. Your experience suggests that those wires may indeed make a difference for shielding performance. It would be good if the next person to shield their cavities with paint records some sound files before and after adding the cavity ground wires. ;)

I would not call it 'grounding noise' though. It would be the lack of grounded shielding which would allow EMI to enter the guitar's wiring, when in noisy environments; grounded shielding would prevent that. In addition to the guitar's wiring, SC pickups like the JM's of course are also susceptible to such noise (and perhaps the greater noise culprits ?). Recent Japanese Fenders I have seen combat noise by using shielded cabling throughout, which is really a no-brainer, and likely more effective than cavity shielding. The need for cavity shielding could be deemed due to Fender's curious use of unshielded wiring in most guitars.

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"I just knew I wanted to make a sound that was the complete opposite of a Les Paul, and that’s pretty much a Jaguar." Rowland S. Howard.

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