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Combined ground wires

HERSCHEL

Member
Messages
5,485
One of the things I have a tough time with is the ground "wad" on the back of the volume pot. With my current project, it's also a fair distance from the pickups to the pots. Has anyone tried, or had issues, with combining ground wires from the pickups and running a single wire to the pot for grounding? That could turn seven solder joints at the pot down to three or four four.
 

specialidiot

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Platinum Supporting Member
Messages
3,485
One of the things I have a tough time with is the ground "wad" on the back of the volume pot. With my current project, it's also a fair distance from the pickups to the pots. Has anyone tried, or had issues, with combining ground wires from the pickups and running a single wire to the pot for grounding? That could turn seven solder joints at the pot down to three or four four.
In theory it would work but it is possible to introduce a ground loop. You really want a common place to run all grounds to home.
 

specialidiot

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Platinum Supporting Member
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3,485
there are no ground loops inside a passive guitar, that's not really a thing. ground is ground, wherever is convenient and reliable to connect ground is fine.
until you plug it in to something. Chances are the amp is in proper shape but not always.
 

testing1two

Platinum Supporting Member
Messages
2,477
You can use a solder lug washer that screws into the body in the control cavity like this:


Or you can get a lug washer that actually fits on the vol/tone pot like this:
 

walterw

Platinum Supporting Member
Messages
37,588
until you plug it in to something. Chances are the amp is in proper shape but not always.
that's not really a factor; there is only one ground potential in a guitar, and that's the shield of the cable. there's also no voltage or current to speak of in there, so electronically it doesn't matter how the internals connect to that potential, as long as they do.

amp problems are a separate issue
 

Timtam

Member
Messages
2,070
I never solder everything (or indeed anything) to the back of pots. To me it just reeks of 1950's "quick and dirty". Never seen it anywhere else in electronics. OK if people understand the issues and deem it the least onerous approach, but a lot of people just do because everyone else does. Instead, create a common ground point (or several) nearby, like a tab screwed into the cavity shielding. Run all your grounds to it. You can even give each ground wire its own tab and screw them all down with one screw at one point. Easy to remove if ever needed.

And as others have said, that's nothing to do with (avoiding) ground loops. You can't draw from situations where there can be a potential difference between ground points (eg with two different wall socket ground potentials) to ones where there can't, ie in a passive guitar circuit. Just having a physical loop (if you do) does not make it a hum-producing ground loop.

On guitars with pickguard shielding or metal control plates, the pots themselves are grounded if connected to the grounded shielding/plate. So your pot bodies don't actually need separate ground wires in that case. You'll see some Fenders like that (as if the wiring designer tossed a coin ... "Ground wires between pot bodies in this one ? Heads or tails ?"). Some people worry about the pots coming loose, but if pots come loose you have a bigger problem (that you know how to fix) ... before loss of ground becomes an issue. Most pots in electronics are grounded to the case that way. But if you really want to ground your pot bodies with a (redundant) wire, use a solder lug washer as suggested earlier.
 

ylo

Member
Messages
702
"I never solder everything (or indeed anything) to the back of pots. . . "

Thank you. Now I know I'm not the only one, and I'm not crazy. To me, it always seemed like a good way to toast the pots!
 

Alanko

Member
Messages
191
To answer OP's question, I wouldn't so it. I like having explicit, individual ground wires for every pickup, bridge and shielding. Splicing two grounds together would be a nice space saving idea, but it gives you more work to do if you want to replace one of the pickups or have to flip the phase of one pickup. You might want to differentiate between the ground for the chassis/cover of the pickup and the wire from the end of the pickup coil.

In theory it would work but it is possible to introduce a ground loop. You really want a common place to run all grounds to home.
I've always been skeptical of the issue of ground loops in passive instruments. I think it stemmed from that Guitarnutz webpage, where an electronics engineer took a look at Strat wiring and reasoned that the typical Strat contained ground loops. I don't recall anybody worrying about them before that.

Saying that, I try and star-ground my guitars where possible as it is a neat way of checking that every ground wire is present and correct.

with good pots, a good iron and proper technique not at all, and it's turned out to be reliable in guitars for oh about seventy-five years now

mechanical connections come loose and oxidize over time, unstressed solder joints are forever
I stopped trashing pots when I got a hot iron. I used to have a small Weller iron you plugged straight into the wall, and it took ages to heat up the back of the pot enough to get solder to adhere. This usually lead to me using too much solder as well.

A good hot iron means you can get in and out quickly.
 

walterw

Platinum Supporting Member
Messages
37,588
I stopped trashing pots when I got a hot iron. I used to have a small Weller iron you plugged straight into the wall, and it took ages to heat up the back of the pot enough to get solder to adhere. This usually lead to me using too much solder as well.

A good hot iron means you can get in and out quickly.
me too, but also there are key techniques i was missing that make it possible to get good joints even with a less than awesome iron without cooking the pot.

for those playing along at home, the three lesser-known "secrets" if there are any to soldering are
1 the solder bridge
2 the life cycle of flux
3 solder flows towards the iron

1 the solder bridge is a hanging liquid drop of extra solder that you put on the iron right before you hit the work; this droplet will be as hot as the iron and will thus transfer heat to the part way faster than just a dry iron tip contacting the part at one tiny point. it's like how food cooks faster in a frying pan with some kind of oil to better transfer heat.

2 flux has to be in the mix while the solder is being melted, otherwise the solder won't flow in and make a clean joint; flux also "cooks" and goes away as soon as the solder does melt, after which the solder will just blob on top and not stick right. (that's what the fumes are, cooking flux)

that's why you're supposed to have the parts touching, then have the iron in one hand and the solder in the other; you're running in fresh solder while the parts are together, that fresh solder has flux inside it, and with that flux the solder will flow in and make a good joint. this is why you can't just make two solder blobs then afterwards hold them together and re-melt them with the iron, all the flux is cooked away and they won't flow together right.

a trick for that situation is to add a little flux, like from a bottle or even a flux pen (like a sharpie with solder flux instead of ink); do that and you can re-melt old solder and have it flow into a good joint.

3 the solder does in fact flow towards the iron, which is why you have the iron on one side of the joint and the solder coming in from the other side; done right (solder bridge droplet on the iron, fresh flux present) the solder will "soak in" across the parts on its way towards the iron and make the joint fast and pretty.

this is my crude explanation of what i learned from the Soldering Mega Thread stickied at the top of this forum, everybody should spend some time watching @John Coloccia's excellent tutorials about how soldering is really done
 
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Timtam

Member
Messages
2,070
I've always been skeptical of the issue of ground loops in passive instruments. I think it stemmed from that Guitarnutz webpage, where an electronics engineer took a look at Strat wiring and reasoned that the typical Strat contained ground loops. I don't recall anybody worrying about them before that.
Yeah I remember that. Wasn't he also the guy that wanted to put a high voltage capacitor on every guitar's output jack to reduce electrocution risk ? I'm not saying he was definitely wrong, as he probably has more formal qualifications in electronics than I do, but sometimes people take what they know really well from their specialist area and try to apply it somewhere else, and miss the mark somewhat, because the context is different. For example, guys who want to apply amp wiring practices to guitar circuits.

We had an EE here some time ago that felt there was a risk of a ground loop in a guitar generating current flow (ie hum) in the ground lines by EM induction (IIRC) - ie the loop could act as an antenna. That is, different to the common mechanism that most audio engineers are familiar with - different ground potentials at different mains power sockets.

Unfortunately we don't have good experimental research to prove or disprove some of this stuff. Yet we have people like some pickup manufacturers repeating ground loop hearsay on their websites. When it would be dead easy for them to demonstrate it if it's true .... just connect up a guitar with a loop in a noisy electrical environment, record the noise level, then break the loop, then record again, then post on youtube. ;)
 

walterw

Platinum Supporting Member
Messages
37,588
Yeah I remember that. Wasn't he also the guy that wanted to put a high voltage capacitor on every guitar's output jack to reduce electrocution risk ?
that's a thing i remember, but the idea was to put the big cap between the string ground and ground so as to avoid shock when touching a mic or whatever while holding the guitar

i tried it on my tele a long time ago, and i found that it took like two 1μF caps in parallel (for 2μF) to actually make the buzz go away when touching the strings, otherwise it wasn't much different from having the string ground disconnected entirely.

i long since got rid of it, the days of weird ungrounded PA systems are mostly over
 

Timtam

Member
Messages
2,070
There are also the EEs who say we should separate 'chassis' ground and signal ground in guitars. ;)
 

Mark Robinson

Platinum Supporting Member
Messages
8,379
“the Solder bridge” indeed Walter. I was told it’s a good idea to place the pot in the middle of travel, supposed to allow the heat to do less harm?
 

walterw

Platinum Supporting Member
Messages
37,588
There are also the EEs who say we should separate 'chassis' ground and signal ground in guitars. ;)
i remember that one, i'd actually tried it at the same time!

the idea was to isolate all the metal bits on the guitar off ground with the cap, so that everything including shielding, the bridge and strings was on the other side of the cap and only the pickup returns themselves directly connected to the cable ground.

i don't recall it making a damn bit of difference in noise level
 

John Coloccia

Cold Supporting Member
Messages
9,580
re: "ground loops" or anything else in "passive" instruments.

In what sense can anyone consider an electric guitar a passive instrument? Maybe if you play it acoustically and amplify it with a mic?

Otherwise, it's plugged into an amplifier of some kind. Do you think it makes a difference to the electrons and photons that the guitar isn't somehow bolted to the amplifier? Do you think it makes a difference that an "active" pickup somehow lives in the guitar as opposed to living in the amp?

Exactly in what sense is a "passive" guitar passive? Because there's a physical wire? If the amp were in the guitar would it then be "active?"

This is very simple. Once you plug your instrument into an amplifier, your instrument is no longer "passive." It doesn't matter that parts of the electronics live at the end of wire. They ALWAYS live at the end of a wire. If you think that making the wire longer makes any difference, you're right only in that it can only ever make matters worse, not better.

There ARE more prevalent problems with so-called "active" instruments, only is as much as the people that install those devices are often not qualified to do so, do a lousy job, and essentially botch up installing an amplifier in the guitar....and the amplifier outside of the guitar will only happily amplify the screwed up signal and make it even worse.

And it's also more difficult to botch up a "passive" guitar because the amp is generally not optimized to behave as a tuner and therefore generally doesn't. It's not like you just toss a bunch of wires and tubes together and all of a sudden you get something that behaves like a radio, other than by accident.

But there is no such thing as a "passive" guitar unless it's not amplified except by acoustic microphones. Yes, if you have ground loops, you increase the chance of your guitar acting as an antenna that can pick up unwanted signals. Guaranteed? No, of course not. That would be FANTASTIC! Radio manufactures would have gone out of business. Just randomly toss together some wires in a loop and listen to radio. LOL.

Increase the risk? Yup.

Easy to avoid? Yup.
 

Alanko

Member
Messages
191
There are also the EEs who say we should separate 'chassis' ground and signal ground in guitars. ;)
I only figured this out when I wanted to swap the phase of the neck pickup in my Telecaster. If you simply swap the hot and ground wires you end up with the pickup cover being live, which can introduce noise if you touch it. Uncoupling the link between the ground wire and the cover ground allows you to keep the cover grounded, separately, regardless of the phase of the pickup coil.
 




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