Mustang finished - major 60 cycle hum

jbone

New member
Messages
3
I just finished my first project: a Warmoth Mustang body and neck, Dakota red.  I'm very happy with it, except that it's humming like crazy.  I noticed in the wiring instructions that it shows a ground wire to be connected "to brass".  I did a little research and found some pictures that show the brass plates in the bottom of the pickup and control cavities, but can't find any detail about what they are (thickness etc.) and exactly what function they serve (shielding, tone effect).  I think it's a shielding issue because it goes away when I touch the control plate.

If anyone has some info on the proper way to shield/ground the cavities, I would be most appreciative.  I've shielded a couple of Teles and Strats, so if it's just a repeat of that method, it shouldn't be a problem.

Thanks in advance.

Jay
 

exalted

Senior member
Messages
723
I have a Jazzmaster with Mustang switching options.

I wired it up and had horrible hum - even with humbuckers. I finally took it into a luthier, put new pickups into it, new switches, new pots, new wires...and it still hummed like crazy.

The luthier said he thought it was the low-quality switches. These were Switchcraft, mind you, and the most expensive ones I could find.

It might just be an idiosyncrasy of the wiring method/switch type.

Eventually I just bored out one of the tone pot holes and added a Les-Paul style switch. Humming gone. Unfortunately, my JM is rear-routed, so I'm stuck with those ugly switch holes...but oh well.
 
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8,318
You could take it to Europe, their hum is only 50 cycles.  I joke of course.  Sounds like a grounding/shielding issue, but that's what single coils do.
 

Keyser Soze

Senior member
Messages
206
Is there any way you could post a diagram (drawn from the actual wiring - not a stock schematic) or photo of the wiring job?

When you get 60 cycle hum from a humbucker there is a problem with the wiring, typically it is a faulty ground, or a grounding wire that is mistakenly connected to the output.

Any shielding that is not properly grounded may also reflect noise into the  circuit, making things worse than expected.

 

exalted

Senior member
Messages
723
Yeah, I know. Like I said, the Mustang switches that are out there are terrible; one physically broke right after I pulled it out of my guitar (I had used it maybe less than two dozen times).

My luthier has been in the business since the late '70's, so I trust him well enough. If he says it's the switches that aren't grounding properly...then it's probably the switches.

Especially if I was able to rewire the whole thing and eliminate the problem. My soldering is horrid.  :laughing7:
 

jbone

New member
Messages
3
The switch issue is an interesting thought.  I'm going to try shielding the cavities (similar to the standard Tele/Strat type shielding method) and hope that it takes care of the issue.  If that doesn't work I'll look hard at the switches.  Is there a way to measure something on the switches to see if they are bad?

I'll try to get some pictures of the wiring job.  I actually built this for my 9 yr old son, and had him do most of the actual soldering (after I made all of the wire connections).  I watched him very closely and I don't think there are any cold solder joints that might be causing it, but I could be wrong.

Thanks for the help!

-Jay

DSCN4247.jpg
 

blue313

Senior member
Messages
2,824
There is a way to measure the hum, but it requires more than the average multimeter can handle.  Bypass the switch terminals and see if it still hums.
 

Keyser Soze

Senior member
Messages
206
Are those single coil sized humbuckers?  Or have you wired them in series as an effective humbucker?  The reason for the question being that while two single coils wired properly can become a humbucker often the result is something less than ideal. 
Any difference between the two coils (say one -ie.the bridge - PU has more winds) and the hum cancellation is not perfect.  Ninety percent hum rejection still leaves ten percent hum - which sounds just like 100% hum when the strings are otherwise silent.

Also, if they are true single coils then you really should do a complete shielding job on the cavity.

Your OP also notes "I think it's a shielding issue because it goes away when I touch the control plate," which also indicates something somewhere is not properly grounded.  Do you have a multimeter?  Anything that is not signal needs to be in continuity with ground.  Preferably with no ground loops.

http://www.guitarnuts.com/technical/noisebucket.php



 
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8,318
Touching the strings (not just the control plate) should eliminate the hum, apparently all metal parts not electrically continuous.  Also, the humbucking effect works in parallel, not just series.  It just yields a different output, but still humbucking nonetheless.
 

jbone

New member
Messages
3
I fixed the problem yesterday.  I used copper tape to shield all cavities and underside of the pickguard.  I also cut a piece of the copper tape and placed it so that it was located over one screw hole from the control cavity, the bridge, and the pickguard.  This tied all three together, and grounding the bridge at the same time (which, as Keyser Soze noted, could not have been grounded previously).

Also, I did have a bad solder joint, and it wasn't one that my son did (unfortunately I can't blame him).  I was having a hell of a time soldering the ground wire to the casing on the switches.  I ended up putting a big gob of soder directly from the lug to the tab on the casing (bad idea).  When I put a multimeter on it (yesterday) and moved the wire, the continuity dropped out.  So I ground down a spot on the side of the casing to remove the plating and soldered the wire correctly. 

It is very quiet now and sounds great!

Thanks to everyone for the help.

-Jay
 
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