Understanding how ground works in guitar wiring

[sonikelectrik]

Looking to either confirm or correct my assumptive thinking on how ground works in guitar electronic wiring. As Im working on a couple of projects and encountering problems, I need to know its down to faulty assumptions on my part.

As I understand it, all metal components in the system (bridge, pots, switch, pickups, jack) need to be grounded to earth. This is achieved by connecting those components to the jack, which passes the ground signal to the amp, which in turn sends it to the AC mains and on to the ground/earth circuit of the house/building.

The ground side of the system 'completes' the circuit and so if anything is not connected to ground it won't work.

When copper shielding is used in the cavity, that can be used as common ground, where all components can be connected to. I use a lug washer screwed into the cavity, with all ground wires soldered to the lug.

I look forward to being proved right, or proved wrong and shown the error of my ways.

Thanks
Adam

[newey]

Mar 21, 2021 13:32:40 GMT -5 sonikelectrik said:

As I understand it, all metal components in the system (bridge, pots, switch, pickups, jack) need to be grounded to earth. This is achieved by connecting those components to the jack, which passes the ground signal to the amp, which in turn sends it to the AC mains and on to the ground/earth circuit of the house/building.

OK, let me preface this by saying that this is all quite a bit of oversimplification. Ground cannot really be thought of as a fixed entity or a fixed location. But we talk about it as if it were, just for ease of conversation.

In the above statement, you are conflating two separate things. First, we have to "ground" our signal-carrying circuit, running through our pickup coils, through the various switches and pots, then, as you say, to the output and ultimately to the amp, etc. If not grounded, we do not have a complete circuit and won't get a signal from the pickups to the amp/speakers.

But the bridge, metal pot cases, switch frames and so forth are typically grounded so as to reduce noise that they might be inducing into one's signal. These things do not have to be grounded, your guitar will work perfectly well if you didn't ground the bridge or the cases of the pots, etc. It just might be noisier. Or not, it depends on a lot of things, but the possiblity that noise might be induced by not grounding those items leads all manufacturers to do so.

Many of the old hollow-bodied "Jazz box" guitars did not ground the bridge. Of course, they weren't being played through some hi-gain pedal into a 100 watt amp either . . .

When copper shielding is used in the cavity, that can be used as common ground, where all components can be connected to. I use a lug washer screwed into the cavity, with all ground wires soldered to the lug.

That is what I do as well, with the proviso that you are running a wire from the lug washer to the jack sleeve lug. You are most emphatically NOT using the shielding as a common ground, you are using the lug washer as a common ground, and the washer is then wired to the output jack.

The idea is that we don't want our guitar signal running contiguous with our shielding until the shielding side meets the signal side, in our case at the lug washer right before the jack. The cavity shielding is then grounded via contact with the lug washer, connecting to the jack via the wire from the lug washer. And, as you say, all other ground wires are collected there as well.

[sonikelectrik]

Mar 21, 2021 13:56:44 GMT -5 newey said:

In the above statement, you are conflating two separate things. First, we have to "ground" our signal-carrying circuit, running through our pickup coils, through the various switches and pots, then, as you say, to the output and ultimately to the amp, etc. If not grounded, we do not have a complete circuit and won't get a signal from the pickups to the amp/speakers.

But the bridge, metal pot cases, switch frames and so forth are typically grounded so as to reduce noise that they might be inducing into one's signal. These things do not have to be grounded, your guitar will work perfectly well if you didn't ground the bridge or the cases of the pots, etc. It just might be noisier.

Ah, see I knew I had parts of it confused. Did not know that. So one could begin with just grounding the 'circuit' and see where one was to keep things simple to begin. Then ground the components once the audio signal was confirmed as working.

You are most emphatically NOT using the shielding as a common ground, you are using the lug washer as a common ground, and the washer is then wired to the output jack.

Indeed, poorly worded by me, I knew that

So one question I have with this set up, when components (pots/switches/etc) come into contact with the shielding isn't the idea that they are now grounded? Does that negate the need for a wire? Does adding a wire introduce a ground loop?

The idea is that we don't want our guitar signal running contiguous with our shielding until the shielding side meets the signal side, in our case at the lug washer right before the jack. The cavity shielding is then grounded via contact with the lug washer, connecting to the jack via the wire from the lug washer. And, as you say, all other ground wires are collected there as well.

As always newey your advice is greatly welcomed and deeply appreciated.
Adam

[unreg]

Mar 22, 2021 0:25:31 GMT -5 sonikelectrik said:

So one question I have with this set up, when components (pots/switches/etc) come into contact with the shielding isn't the idea that they are now grounded? Does that negate the need for a wire? Does adding a wire introduce a ground loop?

hi. “Ground loop” does not exist inside a guitar. Star grounds, just like your washer, are possible bc guitar electronics are ground-loop-free.

If the shielding is grounded directly to your jack then, yes, anything that comes in contact with your shielding is grounded. (As long as your shielding is conductive.) “Directly to your jack” bc you always, like newey said, should avoid running shield ground through signal grounds. Shield and signal grounds should remain unconnected until they reach the jack so as to avoid unwanted noise in your guitar circuit. 👍


Sry, I withdraw my struck-through statements bc they are wrong 😔, as newey and reTrEaD point out below.

[newey]

Mar 22, 2021 0:58:31 GMT -5 unreg said:

hi. “Ground loop” does not exist inside a guitar. Star grounds, just like your washer, are possible bc guitar electronics are ground-loop-free

Well, no, ground loops can (and do) exist in a guitar. They just aren't a matter of concern.

So one question I have with this set up, when components (pots/switches/etc) come into contact with the shielding isn't the idea that they are now grounded? Does that negate the need for a wire? Does adding a wire introduce a ground loop?

Yes, and that's typically what I do, not because I'm worried about ground loops but because I'm worried about soldering to the backs of pots. And why wire superfluous connections?

However, be cautious with this and check the grounding of each component with a multimeter before buttoning things up. I check grounding across the shielding, point to point, and then from each pot or switch to the output jack sleeve. Grounding something by contact is not as sure as soldering a wire, so one needs to be sure the grounding is good.

And I always run a separate wire from the bridge ground to the grounding point, I don't rely on the shielding to carry that ground. No reason why the bridge ground couldn't just be soldered to the shileding, I suppose, but in rebuilding already-existing guitars, the wire is usually there already anyway, and I've just gotten in the habit of running that wire all the way to the grounding point, seems more secure that way. IDK.

So one could begin with just grounding the 'circuit' and see where one was to keep things simple to begin. Then ground the components once the audio signal was confirmed as working.

See above re: using the shielding to do the grounding. Whether one runs wires or uses contact with the shielding, you're going to do it eventually anyway, or at least you should do so. Again, guitar manufacturers are not just wasting wire for no reason. So might as well take care of it while you're doing the job instead of having to go back in later. If this is a Strat-ish type guitar, if you are using the shield to ground things, the pickguard has to be mounted before that contact is made, so if you're testing the circuit with the pickguard off, then the pot shells, etc aren't grounded yet anyway.

[reTrEaD]

Mar 22, 2021 0:58:31 GMT -5 unreg said:

hi. “Ground loop” does not exist inside a guitar. Star grounds, just like your washer, are possible bc guitar electronics are ground-loop-free.

If the shielding is grounded directly to your jack then, yes, anything that comes in contact with your shielding is grounded. (As long as your shielding is conductive.) “Directly to your jack” bc you always, like newey said, should avoid running shield ground through signal grounds. Shield and signal grounds should remain unconnected until they reach the jack so as to avoid unwanted noise in your guitar circuit. 👍

If you understood how ground loops work, you probably wouldn't make such bold (and incorrect) statements.

A ground loop exists in virtually all guitar/cable/amplifier systems. Fortunately the currents in shielding circuit are low and the resistance in the ground circuit is very low, under normal circumstances. But faulty solder connections can introduce enough resistance to make the ground loop issue a significant problem.

[sonikelectrik]

Mar 22, 2021 6:18:03 GMT -5 newey said:

Yes, and that's typically what I do, not because I'm worried about ground loops but because I'm worried about soldering to the backs of pots. And why wire superfluous connections?

Indeed. This is my motivation too. I'm a bit (lot) OCD and I like a tidy cavity (don't we all mate wink wink). I also learned to do this when I had a cheap low power iron that was not capable of getting the back of a pot hot enough to melt solder. Old habits and all that.

However, be cautious with this and check the grounding of each component with a multimeter before buttoning things up. I check grounding across the shielding, point to point, and then from each pot or switch to the output jack sleeve. Grounding something by contact is not as sure as soldering a wire, so one needs to be sure the grounding is good.

Yeah that's what I did. In fact if you see my other thread with my problem installing my sons active pickups I have some meter readings that check from shielding to various components. I'm assuming a continuity beep, and no/low resistance is desired result here? Is there a condition/result on the meter that would suggest a bad/weak ground?

And I always run a separate wire from the bridge ground to the grounding point, I don't rely on the shielding to carry that ground. No reason why the bridge ground couldn't just be soldered to the shielding, I suppose, but in rebuilding already-existing guitars, the wire is usually there already anyway, and I've just gotten in the habit of running that wire all the way to the grounding point, seems more secure that way.

Yeh the bridge ground is not an issue as you point out. Its already there and theres enough wire to get directly to the jack.

If this is a Strat-ish type guitar, if you are using the shield to ground things, the pickguard has to be mounted before that contact is made, so if you're testing the circuit with the pickguard off, then the pot shells, etc aren't grounded yet anyway.

Well I HAVE done this on my Strat and yes understand that the pick guard will create that cage of copper once sealed. In this case its my sons BC Rich which is like a Les Paul with cavity accessed from the back. Pots go thru the front wood so are always in contact with the shield. Good point though.

So the question about the ground loop I raised I was thinking about the pot that is in contact with the cavity shielding - assuming the connection is good and the meter gives a continuity beep - is any other ground wire superfluous? No wire needed from the 3rd lug? Or is that grounding the internal wiper?

Thanks a bunch, this has been quite an educational thread
adam

[newey]

Mar 24, 2021 0:47:16 GMT -5 sonikelectrik said:

No wire needed from the 3rd lug? Or is that grounding the internal wiper?

As you turn the knob, yes. That connection is part of your signal chain. You need that one.

I'm assuming a continuity beep, and no/low resistance is desired result here? Is there a condition/result on the meter that would suggest a bad/weak ground?

Yes. Your meter should show no more than a few Ohms. If it gets up into double digits, could be a faulty connection.

[sonikelectrik]

So one thing I’ve been struggling to understand the past few days is why the bridge needs to be grounded. It doesn’t carry an electrical charge does it? So why does it need a ground?

i know I’ve read stories of gutrarists getting electrical shock from poorly grounded instrument and I imagine the bridge has a role to play there. I just don’t understand how that happens, and would like to understand better.

thanks
adam

[reTrEaD]

Apr 9, 2021 11:02:01 GMT -5 sonikelectrik said:

So one thing I’ve been struggling to understand the past few days is why the bridge needs to be grounded. It doesn’t carry an electrical charge does it? So why does it need a ground?

Since you're usually touching the strings while playing the guitar, that's a convenient way to ground your body. This is important because your (ungrounded) body can help couple electromagnetic hum and noise from the environment to the guitar, particularly the pickups.

John S. Atchley had an article on the original Guitarnuts website. Here's a reprint of that article:
You're just a big ol' Bucket O' Noise

[sonikelectrik]

Apr 9, 2021 11:19:02 GMT -5 reTrEaD said:

Apr 9, 2021 11:02:01 GMT -5 sonikelectrik said:

So one

Since you're usually touching the strings while playing the guitar, that's a convenient way to ground your body. This is important because your (ungrounded) body can help couple electromagnetic hum and noise from the environment to the guitar, particularly the pickups.

John S. Atchley had an article on the original Guitarnuts website. Here's a reprint of that article:
You're just a big ol' Bucket O' Noise

Ah fascinating, so it’s more to do with the human element. So without that bridge ground, touching the strings could/would introduce hum, buzz, noise from the environment through the ungrounded human body. Thus, if that phenomenon happened it would/could be a good indicator of a bad bridge ground.

I ask as this was a problem a while back on one of my strats

Cheers
Adam

[newey]

Apr 9, 2021 16:32:59 GMT -5 sonikelectrik said:

So without that bridge ground, touching the strings could/would introduce hum, buzz, noise from the environment through the ungrounded human body

If the bridge ground is functioning properly, the noise level should reduce if you touch the strings- as reTrEaD said, you're grounding any noise that is being "channeled" by your body. If there was no bridge ground, you should hear the same level of noise whether you are touching the strings or not.

[unreg]

Mar 24, 2021 5:31:04 GMT -5 newey said:

Mar 24, 2021 0:47:16 GMT -5 sonikelectrik said:

I'm assuming a continuity beep, and no/low resistance is desired result here? Is there a condition/result on the meter that would suggest a bad/weak ground?

Yes. Your meter should show no more than a few Ohms. If it gets up into double digits, could be a faulty connection.

hi again Adam,

I remember having a conversation in a guitarNuts2 thread where I learned that even something like 0.6% resistance was too high/not conductive enough for grounding. I think resistance is different from continuity, but either can be used for ground checking.


I experienced a problem where, after soldering a wire between my two potentiometer-cases and soldering a wire from my vol pot’s case to its ground lug, my multimeter measured 0.6% resistance between either pot and my guitar’s jack.

Thought you may be helped by reading what I discovered in a conversation with wise frets (this is me speaking):

While following the ground path, I removed the paperclip from the wall so I could check it. The second to last wire on that star ground paperclip went to my volume pot, and it registered a 0.6% resistance. So, I heated that tiny loop and applied a bit of solder; there wasn’t much solder there to begin with; now the resistance to either pot from the jack is 0.0%! 😀

Now my guitar is nice and silent! 😀 Hope this helps you.


Oh, yes, the star ground paperclip, newey’s idea, is just screwed into the painted cavity wall; tons of ground wires, including the jack’s ground, are soldered to it. Wise frets had me add those wires that ground the pot cases.