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"Loaded" Pickguard Hum While Outside Of Guitar Body

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  • "Loaded" Pickguard Hum While Outside Of Guitar Body

    Hi all,

    I'm working on building a loaded pickguard from scratch. This is the first time I've done anything more than an PUP swatch. I have learned a lot and I'm nearly at the finish line to put it into my Strandberg.

    However, I've run into dreaded hum.

    While testing my wiring, I notice that I have what seems like a ground loop hum. I am 99% confident that my solder joints are good and that I only have 1 single path to ground from each component.

    I'm not sure if I have a ground loop or if I am getting this hum only because the guitar is outside of it's faraday cage home inside a shielded cavity -- and it's not actually grounded to the trem claw yet.

    In a nutshell, my question is:

    Is a 'loaded' pickguard as quiet as it will be INSIDE of a guitar while it is OUTSIDE of a guitar?

    When I touch the output jack or the active lead on the switch(es), the hum goes away -- so it _seems_ like a ground loop.

    As a newbie, though, I'm not sure if this is "normal" for when a pickguard is OUTSIDE of a guitar?

    Here is a video showing the hum and some troubleshooting "touches":
    https://www.youtube.com/watch?v=3iW1mfqPucg

    Some more troubleshooting data that I do not have in the video:
    - When I turn the volume pot down below 10, starting at 9 the hum gets significantly louder. It's much quieter when the volume pot is max'ed. Video here: https://www.youtube.com/watch?v=USwcP8RQzRA
    Last edited by tmbridge; 10-30-2020, 01:33 PM.

  • #2
    It is quite impossible to get a ground loop problem in guitar electronics wiring. Also ground loop hum wouldn't change when touching.

    I suspect you have a missing ground connection. Do you get zero DCR between shielding foil and ground pin of the jack?

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    • #3
      Run jumper wire ground to strings or bridge.

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      • #4
        Originally posted by Helmholtz View Post
        It is quite impossible to get a ground loop problem in guitar electronics wiring. Also ground loop hum wouldn't change when touching.

        I suspect you have a missing ground connection. Do you get zero DCR between shielding foil and ground pin of the jack?
        Thanks for the reply.

        No, when I test DCR between foil and ground on the output jack, i get infinity. However, when I do this test, the hum disappears. Does this mean the jack isn't grounded? Video: https://www.youtube.com/watch?v=Op4ii2UpSCE

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        • #5
          Originally posted by mozz View Post
          Run jumper wire ground to strings or bridge.
          This is how it will be once I put the pickguard into the guitar -- so are you saying that the hum I have no is a by-product of the fact that the pickguard is not mounted in a guitar yet?

          I did try hooking up the ground 'nexus' to the trem of a guitar (without actually mounting the pick guard into it) but the hum persisted.

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          • #6

            No, when I test DCR between foil and ground on the output jack, i get infinity. However, when I do this test, the hum disappears. Does this mean the jack isn't grounded? ]
            That's what I guessed.

            Either the foil or the jack isn't properly grounded. Why is the green ground wire not soldered to the foil?
            For convenience you may just wire an additional wire from your "star" ground the jack's ground pin.

            As I cannot exclude a wiring error, check if you get a signal when lightly tapping the PUs with a steel object (e.g. screwdriver) after installing the additional ground wire. A vibrating tuning fork held closely over the PUs should produce a nice(r) signal.
            Last edited by Helmholtz; 10-30-2020, 03:56 PM.
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            • #7
              Originally posted by Helmholtz View Post


              That's what I guessed.

              Either the foil or the jack isn't properly grounded. Why is the green ground wire not soldered to the foil?
              For convenience you may just wire an additional wire from your "star" ground the jack's ground pin.
              Thank you so much!

              The problem boils down to probably what is the most common mistake in guitar wiring -- a reversed output jack.

              I'm using an integrated clean buffer/output jack and am also wiring it on/off in the push/pull volume. This made the output jack install more complex than normal



              I flipped the blue and brown -- and, boom, silence.

              Now, to hope I can actually fit this Redeemer + 9v into the cavity of a Strandberg -- i don't think it's likely that it'll fit but I might try to replace the 9v with 3x3v Lithiums. if not, I'll just use a regular output jack and, hey, I learned a lot getting it working!

              THANK YOU!

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              • #8
                If it has not been mentioned before, make sure your (ground) connections have a single path back to the jack's ground- and that includes the switch pots!!!

                The attached photo shows how the foil was removed around the switch, pots, pickups etc. I created a "moat" of dead space. Let's talk about the pots. You can see the black wires making a ground connection between the pots. The pot with the most glob then has a single wire that will go to the jack when I install the cover back on the guitar. The jack will then have a second ground wire that connects to the foil. So in the configuration shown, I do NOT have a connection between the case of the pots and the foil. Test with a meter to confirm infinite resistance. The same is true for the switch. That too has a black wire connecting the case of the switch to the pot with the glob!!

                In this particular (cheap) guitar, I used aluminum foil. Is it any better or worse than copper foil? Eh, who really knows. But it was an experiment on a project guitar. And I do believe it helped reduce the noise. I had to keep in mind that these were not the best pickups in the world. But I think you will get the idea.

                Good luck...

                Click image for larger version  Name:	Inside Pick.JPG Views:	0 Size:	695.4 KB ID:	916920

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                • #9
                  If it has not been mentioned before, make sure your (ground) connections have a single path back to the jack's ground- and that includes the switch pots!!!
                  I understand the problem was solved.

                  Apart from that, multiple ground connections ("ground loops") - though unnecessary - are no problem inside a guitar as there are no considerable hum/ripple currents in the ground wiring. Simply because there are no strong nearby hum sources.


                  Last edited by Helmholtz; 10-30-2020, 06:40 PM.
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                  • #10
                    Originally posted by TomCarlos View Post
                    If it has not been mentioned before, make sure your (ground) connections have a single path back to the jack's ground- and that includes the switch pots!!!

                    The attached photo shows how the foil was removed around the switch, pots, pickups etc. I created a "moat" of dead space. Let's talk about the pots. You can see the black wires making a ground connection between the pots. The pot with the most glob then has a single wire that will go to the jack when I install the cover back on the guitar. The jack will then have a second ground wire that connects to the foil. So in the configuration shown, I do NOT have a connection between the case of the pots and the foil. Test with a meter to confirm infinite resistance. The same is true for the switch. That too has a black wire connecting the case of the switch to the pot with the glob!!

                    In this particular (cheap) guitar, I used aluminum foil. Is it any better or worse than copper foil? Eh, who really knows. But it was an experiment on a project guitar. And I do believe it helped reduce the noise. I had to keep in mind that these were not the best pickups in the world. But I think you will get the idea.

                    Good luck...

                    Click image for larger version Name:	Inside Pick.JPG Views:	0 Size:	695.4 KB ID:	916920
                    Thanks. I was curious about this exact issue and considered "moating" my components as well but I went on to read up on it and I found that, since there is one terminal point for the ground (at the output jack), it's impossible to have a 'true' ground loop in a guitar itself. I was unsure what to believe until I did it myself and I now have a quiet pick guard, without component moats.

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                    • #11
                      Sorry, I don't understand what "moat" means in this context (foreign language).

                      You can have ground loops in guitar wiring. But generally ground loops only cause a hum problem if there is a strong hum source that feeds a hum current into the loop.
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                      • #12
                        Oh, I was referring to TomCarlos' use of "moat". I took it to mean an area around each component with out the foil -- so the component is not grounded to the foil directly by touching it. You can see it in his photo.

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                        • #13
                          Originally posted by tmbridge View Post
                          Oh, I was referring to TomCarlos' use of "moat". I took it to mean an area around each component with out the foil -- so the component is not grounded to the foil directly by touching it. You can see it in his photo.
                          Thanks for explanation.

                          The method shown doesn't make sense to me. Especially the switch should have a ground contact via the foil.
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                          • #14
                            Yes... "moat" means the area around the pots and switch where there is no foil. The switch is grounded through the black wire that goes to the pot. So we have a single path for ground. I prefer to do that instead of relying on the foil to provide the ground connection.

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                            • #15
                              The point is that there’s no need or benefit from the moat, it’s not a problem to have multiple paths for 0V.
                              Consider that in the instrument cable, would you cut all the screening wires bar one?
                              My band:- http://www.youtube.com/user/RedwingBand

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