Massive ground loop?

Dave Sloven

Dave Sloven

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I have just finished wiring up my Explorer and it does nothing but make an enormous buzzing sound. This is the case for any position on the selector switch. Thankfully I used a cheap Roland practice amp turned down low when I tested this. It's late at night and I have a gig tomorrow night so this is very frustrating!!! I am wondering if this can be fixed with either electrical tape or 'liquid electrical tape' ... both of which I have on hand

I constructed a new harness from MilSpec shielded wire with two DPDT switches, one for a blower/bypass switch for the bridge pickup (a push-push on the bridge volume pot that switches between the conventional wiring and a 'straight to jack' setup) and a series/parallel switch for the neck pickup. The series/parallel switch seems to be very well insulated with both liquid tape and electrical tape so I doubt that is the noise issue; anyway the problem seems to exist no matter where the switches are positioned. But the small size of the control cavity and led me to run the shielded wires down the sides of the neck volume pot, causing the shield on those wires to come into contact with the shielding paint on the sides of the cavity. I suspect this might be the cause of the problem. I used liquid electrical tape around the selector switch (which has been moved into the control cavity, in the neck volume position after deleting the master tone pot) and jack channel. I have had problems with shorts on the jack due to the shielding paint in this guitar before, hence why I was especially careful to use the liquid tape around there. The jack seems to not be shorting out as there is definitely a sound coming out. I suspect what I am hearing is a huge ground loop caused by the connection of the grounds for the bridge selector switch wire and the wire back from selector switch to jack (actually to the relevant lug on the push-push pot, which goes between these).

Here are some photos anyway. I will have a go at lifting the harness out and painting the sides of the cavity tomorrow, but I am wondering if this inarticulate constant hum sounds like a ground loop to people. I am getting none of the usual 'donk donk' sound when I hit a metal object on the pickup poles either

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I've pulled it apart again, desoldered those two wires from either side of the pot and insulated them, hopefully when I get up in the morning and test it through the Randall it will sound like a guitar this time.

Here's another photo, this one showing the control layout

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DonP said:
The jack ground doesn't seem to go to the pot ground.
Click to expand...


It DID, it was soldered to the side of the pot (it grounded through the shield) but I've since desoldered it as stated above. I will test it in the morning but you are right, I might need to solder it to the top of the volume pot

You can't see it in the photo above but basically it was soldered to the other side
 
I could solder those two wires to the top of the neck volume pot but I was worried it might get to congested. Also I am not sure they will reach, and I don't think I have time to pull the whole thing apart before the gig

I am also worried that with all this tugging and pulling I might have broken a connection on the selector switch. Can't tell until the morning when I can plug it in
 
Turned out that the problem was with that tricky push-push blower switch. Removed it in favour of another CTS 550K pot like I used for the neck and all is sweet. Had to do a heap of wire work again though, for the selector switch and jack. Only problem I can detect with the wiring job now is that I wired the DPDT for the neck pickup back to front, so that when it is 'off' the parallel mode is engaged. I will fix that later.

The base tone of the instrument now is basically the same as it was previously when I had the push-push tone bypass engaged. I used to always play with that engaged or the tone on 10 anyway so that doesn't make much difference anyway. What does make a huge difference is having the selector switch in a sensible place!!!!

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