Guitar Grounding (Metal Control Plate)

MitchMev

Member
2015-12-06 7:03 pm
So as I was tightening the nut on the jack on a jazz bass at the school where I teach, I noticed the ground lug had no wire connected. I took it home to fix it, but I realized that the bass wouldn't work if the jack had no ground connection. I noticed that the control plate is conductive and that in fact it is the "central" ground point. The pickup grounds are connected to the back of their respective volume pots which are electrically continuous with the shafts which are connected to the control plate. The bridge ground is connected to the back of one of these pots and the jack is connected to the control plate via the mechanical connection, just like the pots.

So my question is, should I just leave it as is (if it ain't broke, don't fix it) or is it worth rewiring this to improve the grounding? I don't want to mess with it and create ground loops if there is no need.
 

turk 182

Member
2012-10-26 3:03 pm
as someone who's done some guitar tech work over the years i would add a ground wire from the output jack to the volume pots and ensure the volumes are also interconnected. relying on a mechanical connection to maintain a good low resistance connection on something like a jack that can work loose (if proper hardware isn't used) is the quick way to a bad/high resistance/intermittant ground.
you said it was a jazz model but did not mention the manufacturer most would assume that where talking Fender but most school budgets wouldn't cover the real mcoy...
 

MitchMev

Member
2015-12-06 7:03 pm
as someone who's done some guitar tech work over the years i would add a ground wire from the output jack to the volume pots and ensure the volumes are also interconnected. relying on a mechanical connection to maintain a good low resistance connection on something like a jack that can work loose (if proper hardware isn't used) is the quick way to a bad/high resistance/intermittant ground.
you said it was a jazz model but did not mention the manufacturer most would assume that where talking Fender but most school budgets wouldn't cover the real mcoy...
Yeah it's a Fender Standard (made in Mexico) Jazz. It looks like everything is stock but I'm not totally sure.

I was having the same thought myself. The jack was in fact loose so that's why I had the bass opened up.

So I think I am going to go with your advice. Do you think that I would risk creating ground loop issues?

Also should I look into making a ground bus or some other type of star ground or is it good to just go from pot to pot to jack?
 
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Hi Guys

The wiring you described is typical and quite wrong. Truk's advice is correct - change the wiring to have grounds with proper integrity.

The pickup wires should go to the pots, then from the pots to the jacks - with the switches (if any) interposed where they should be. The ground from the bridge should go to the jack.

If the pots have metal backshells and bushings, they should be bolted to a metal plate to provide some shielding with all of these metal bits tied to ground. You often see foil inside the control cavity and this is better than nothing. Ground loops in the guitar are not an issue, and the sequential wiring described above avoids them anyway.

Have fun
 

Gnobuddy

Member
2016-03-01 4:10 pm
That he certainly did!

A Premier Guitar article on Paul Bigsby described Fender this way: "...Leo Fender was not a great inventor, but he was a great innovator, meaning he took existing items and made changes to them that enhanced their performance."

I think that is closer to the truth, particularly if you replaced "enhanced their performance" with "lowered their cost of manufacture without substantially lowering their usability". That lower manufacturing cost probably enabled Leo to stay in business, while many brilliant competing inventors went bankrupt or closed up shop.

Back on topic, there are some strange grounding schemes in old Fender guitar amps too. There were some amps with pots grounded haphazardly through incidental contact with a brass plate. After some years of corrosion and tarnish build-up, the grounds would become unreliable, resulting in symptoms varying from increased hum to receiving mild shocks via the guitar cable. :eek:

-Gnobuddy