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Humming Jazz bass


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7/21/1997 6:35 PM
James Humming Jazz bass
I have an early 70's Jazz bass which has this annoying hum. It stops when you touch the strings or bridge. I have gone through and resoldered every joint and no change. No other guitar I own does this:strats,teles,les pauls/single coil or humbucker. The Jazz is totally stock. Any ideas?  
Thanks  
James
 
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7/24/1997 5:11 AM
Bill Bolton

> It stops when you touch the strings or bridge.  
 
That's normal behaviour for a stock Jazz Bass. When you touch the strings your body is grounded through the bridge and acts as a "ground plane" to shield the bass.  
 
If you want it quieter, you'll need to do a thorough shielding job on the whole bass.  
 
Cheers,  
 
Bill
 
7/24/1997 6:44 PM
James
Bill-Thanks for your response. The guitar seems fully shielded from the factory. There are shields around the pickups, under the pickguard, & in the control cavity. Where would you suggest further shielding?  
Thanks  
James
 
7/27/1997 4:53 AM
Bill Bolton

>The guitar seems fully shielded from the factory.  
 
Highly unlikely!!!!!  
 
>Where would you suggest further shielding?  
 
Check out John Atchely's Guitar Shielding and Wiring web pages at:  
 
http://www.johnatchley.com/guitar/index.html  
 
which will give the full run down on what's usually required.  
 
Cheers,  
 
Bill
 
8/11/1997 10:18 PM
Mark Hammer

One other avenue to try is a "dummy" pickup wired in parallel out-of-phase with the existing pickup.  
 
The "dummy" pickup consists of a coil, matched with the existing pickup for the number of turns, but lacking a magnet or pole pieces. It doesn't have to be exactly the same as the original in any other respects (purists will likely disagree).  
 
Putting these two in parallel results in a pseudo humbucker pickup with only the existing pickup sensitive to string vibrations. Both the existing pickup and the add-on dummy coil pick up electrostatic and RF noise, but cancel each other out when wired out of phase.  
 
You can probably stick the dummy coil in the control cavity. I've done this and it works. Not perfectly, but with a noticeable decline in hum.  
 
Where to get a dummy coil? Guitar repair shops sometimes have a box of crappy pickups that customers left with the repair-person when replaced with something higher quality. The most foolproof type would be one with a ceramic magnet glued to the bottom that you could simply yank off. Magnetized polepieces a la Fender could also be removed, but more skill is needed for this.  
 
Wire one lead to ground, and the other lead to the hot lug on your volume control. Check to hear which arrangement results in the most hum reduction. Once you've got it nailed, stuck the cavity with sponge foam or hot glue the coil to the cavity to keep it from boouncing around.  
 
This does not alter the tone of the original pickup.
 

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