Can a guitar have a 'ground loop'?

simoncroft

Still playing. Still learning!
Silver Member
May 30, 2013
19,683
SE England
In Viking_inLA's massively popular Chinese Guitar Review thread, Didger quoted this from GuitarNuts.com - Shielding a Strat(tm).

"Remove any wires which are soldered from the shell of one pot or switch to the shell of another. These wires are ground loops because the bodies of the controls are also electrically connected through the foil on the back of the pickguard."

Now, I'm not an electrical engineer, so I am asking other forum members if I'm correct. Surely 'ground loops' only happen when you have two or more powered audio devices (ie amplifiers, mixing desks etc) in the same audio chain and they are connected to both the same mains ground (Earth if you're a Brit) and through the electrical shielding of the unbalanced audio cables. (That is to say, there are no audio isolation 'balancing' circuits on the I/O to prevent this from happening.)

As far as I understand it, a ground loop is caused in a difference in 'potential' between the AC mains side of the circuits and the audio side.

How could that possibly happen inside a passive guitar, when all you are doing is hooking up a few pot casings two different ways for maximum reliability?

I'd be the last to say anything on a guitar 'makes no difference to the sound' but I've been adding extra ground wires to pots for years and I'm pretty sure I've never created a 'ground loop'.

Anyone prepared to argue the case on a technical level?
 

fumbler

PhD-Stratology
Oct 22, 2009
5,652
New Joisey!
No, you're correct. Ground loops are only possible in an active/powered circuit like an amplifier where you have different gain stages. The "hot" part of the circuit for one stage might be the "ground" for the next stage. Or when you have two different powered devices like you mention.

In a passive circuit like a "normal" guitar ground is ground. You do not need to do star-grounding for example. As long as you have a good continuous ground where everything connects (eventually) to the jack sleeve, you'll be A-OK. Relying on grounding via a shielded pickguard is dicey; shields corrode and nuts loosen up. I also make a proper soldered wire connection to ground with no problems.

You DO, however, want to avoid unnecessary loops of wire. A loop can act as an antenna (for noise). It's conceivable (but unlikely) that a loop might be perfectly tuned to pick up your local radio station! But don't get too crazy. This is all negated with proper cavity shielding.


From wikipedia:
In an electrical system, a ground loop usually refers to a current, almost always unwanted, in a conductor connecting two points that are supposed to be at the same potential, often ground, but are actually at different potentials.
 

Strato67

Former Member
Feb 19, 2011
2,962
Texas
Nope...there can be no "Star Ground"..its a myth...all ground wires go to the output jack...you would have to have two output jacks to two separate amps...Now on the shielding if your going to use tape... aluminum works better from what I have experienced (copper affects the tone to me)..but it will not get rid of the 60 cycle hum...maybe some of the RFs will not be as prominent...but at the same time I think people over think things and really should just be playing their guitars...Most amps have crappy shielding as well...so I guess Faraday away if that's what you want...I like the shielding paint better and you won't slice up you hands and affect the tone....Just my two cents...and that's all I have...lol
 

JohnDH

Senior Stratmaster
Dec 5, 2012
2,229
Wilton NSW Australia
Yes, don't worry about ground loops in a passive guitar. And Ill speak on behalf of the GuitarNuts forum, since I'm a mod there.

When I first joined up, I tested it by trying to create a massive passive ground loop around a whole room! - there was no extra hum or noise.
 

Viking inLA

Most Honored Senior Member
Oct 23, 2013
5,844
Los Angeles
Yes, don't worry about ground loops in a passive guitar. And Ill speak on behalf of the GuitarNuts forum, since I'm a mod there.

When I first joined up, I tested it by trying to create a massive passive ground loop around a whole room! - there was no extra hum or noise.

Hi. Woul u mind having a look at last page of Chinese guitar thread. I shielded everything and added an extra ground from pot to lug in cavity. Still same old hum. Do you have to wire it specifically if your shielding it?
 

JohnDH

Senior Stratmaster
Dec 5, 2012
2,229
Wilton NSW Australia
I dont see any issue with pot cases being grounded by wires, as well as by shielding contact. The wire is the more reliable path. But shielding only takes some high buzz away as picked up by the wiring. Single coils still hum.
 

simoncroft

Still playing. Still learning!
Silver Member
May 30, 2013
19,683
SE England
Gentlemen, thank you all for your input. I didn't think I could have been doing something wrong for so many years without realising. But I'm always open to reasoned argument.
 

Jack FFR1846

Senior Stratmaster
May 4, 2011
3,806
Hopkinton, MA
In my experience, I've found 3 valid places for hum or pops to enter and can give you the solutions.

1) output jack ground (the tube). It becomes corroded and makes a poor connection with the cable. Roll up some very fine sandpaper (400 is good) and stick the roll into the output jack and sand it for a minute or so. This is the solution more than 90% of the time.

2) output jack wired backwards. Do you get a bit of noise and touch the strings and the noise gets worse? Or you play and the noise is there and you stop and it goes away? If you did work on the jack or it's a new/used guitar to you, likely it's backwards. Anyone can wire it backwards. I do it occationally and I have 3 EE degrees and have worked as an engineer for almost 30 years.

3) Aftermarket pickguard static generator. Some Chinese pickguards create a great deal of static electricity when touched. Whack the pickguard with your finger. If it creates a pop, that's the problem. Take it off. Glue on some aluminum foil. I tend to spray the back with adhesive and drop a piece over the whole thing. Then let it dry, cut out the holes (doesn't have to be neat, nobody will ever see it). Now you need a route to get to grounds. On a strat, it's already done because the pots are all grounded. On a tele, run a piece of thin stranded wire to a pot....solder it in place. Now, run a loop under where the pickguard is (on mine, it goes through the tunnel in the body). Bam.

4) Ok, I lied. There's a 4th I remembered. On a tele, the bridge grounding system from Fender is horrible and subject to corrosion. Pull off the bridge, clean the back well. run a bare stranded wire from the back of a pot and loop it under the bridge. Screw the bridge back down.
 

B. Howard

Strat-Talker
Jun 7, 2013
152
Magnolia DE
The term "ground loop" is not really proper in this situation as already noted but there is some truth to the statement about unnecessary wires. If you have a cavity shielded with foil or conductive paint and then also run traditional ground wires from device case to device case what happens is there becomes multiple potentials to ground from each device. While electricity is lazy and always follows the path of least resistance, these differences are very small so sometimes the electricity can get confused and not flow in a smooth manner towards ground and thereby inducing noise from the cycling of this flow into the signal.If the difference in potential to ground is big enough then electricity will flow the shortest path to ground but also can now create a draw on the other potential to ground pulling signal away from another device and it's ground and again causing our signal to degrade.
 

fumbler

PhD-Stratology
Oct 22, 2009
5,652
New Joisey!
The term "ground loop" is not really proper in this situation as already noted but there is some truth to the statement about unnecessary wires. If you have a cavity shielded with foil or conductive paint and then also run traditional ground wires from device case to device case what happens is there becomes multiple potentials to ground from each device. While electricity is lazy and always follows the path of least resistance, these differences are very small so sometimes the electricity can get confused and not flow in a smooth manner towards ground and thereby inducing noise from the cycling of this flow into the signal.If the difference in potential to ground is big enough then electricity will flow the shortest path to ground but also can now create a draw on the other potential to ground pulling signal away from another device and it's ground and again causing our signal to degrade.

Say what?

How could this happen in a passive guitar circuit with extremely low current flowing through soldered copper wire of a few inches in length?

The only issue with loops in such a circuit is the remote possibility of one being accidentally "tuned" to a strong local source of RF noise and picking it up (just like an old crystal radio). And, if all the circuitry is inside a cavity shielded with metal foil or conductive paint, then this cannot happen.
 


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