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Need help with hum on tone knob

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  • Need help with hum on tone knob

    I have 2 different guitars both wired exactly the same, both with humbuckers but one of them has horrible hum when the tone knob it turned up. It sounds like 60hz hum and does decrease when I touch any grounded part but I'm unsure why one guitar works fine while the other buzzes so much more.

    I'm curious if it is a bad pot or cap, the wiring seems fine, as I said it's wired exactly the same as my other guitar and that works fine. The tone pot does also seem sort of "muffled", it doesn't seem to actually change the tone as much as it seems it should but it is hard to tell if that's just a side effect of the louder humming.

    Both guitars have a bit of 60hz hum but it's extremely quiet even with my amp volume maxed and decent gain once i'm touching something grounded the only outlier is the tone pot on the one.

    Any suggestions on what may be happening or what the cause is will be appreciated. I can also provide pictures of the wiring of both guitars if needed but i've checked and triple checked and they are both exactly the same and the one works perfect.

  • #2
    Make sure your bridge ground isn’t open or resistive.

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    • #3
      A picture of the guitar wiring would be helpful in diagnosing the fault in that we can see how it's grounded and how your cap and pot are connected.. It could be that turning your tone pot up is coupling an ungrounded part of the circuit into the signal path. You say it has a terrible hum with the tone pot turned up, but does it completely disappear when the pot is turned to zero? Check the resistance from wiper to ground when on zero (should be close to 0 ohms) and full up it should read the pot's nominal value. Make sure that the grounds are connected (including the pot shell) by measuring with a DMM rather than by sight. A connection that looks good may not be good electrically.

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      • #4
        Thanks for the replies. when i'm grounded and touching any metal part of the guitar, there is virtually no hum when the tone pot is all the way down, but as it's turned up even if i'm still grounded there is a ton of hum, both my guitars have a bit of 60hz hum so I don't expect it to be completely silent all the time i know they could use some better shielding but it is far worse than my other guitar. The wiring seems fine even with a multimeter, all grounds are connected to the shell of the volume and the tone pots resistance seems fine, its around 480k if turned the right way otherwise 0 as it should be.

        Here's a picture of the pot wiring. I will add audio of it soon just waiting for it to upload.

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        • #5
          Try this.
          Set guitar to maximum hum.
          Clean the guitar jack and plug with a cleaner solvent both tip and ring.
          Apply an alligator clip wire (clip on both ends) to the guitar cable ground plugged into the guitar. Put it directly on the cable ground.
          Apply the other alligator clip end to the following:
          Tone pots ground connections
          Volume pots ground connections.
          Humbucker pickups metal frame.
          Metal bridge that connects directly to strings.

          Let us know in any of these touch points reduces the hum?

          Joseph J. Rogowski
          Last edited by bbsailor; 04-12-2020, 06:18 PM.

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          • #6
            Touching any of them made no difference.

            At this point im almost wondering if its just picking up slightly more 60hz hum than my other guitar for some reason and the tone pot is just making it more noticeable at a higher volume. Is there anywhere specific along the wiring that it could be picking up more hum that the tone pot would increase but not necessarily the volume pot?

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            • #7
              Maybe there's a problem with the pickup in the buzzy guitar, such that it isn't actually bucking hum? High setting of the tone control just making that apparent.
              Check for that by swapping in a known good pickup.
              My band:- http://www.youtube.com/user/RedwingBand

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              • #8
                I thought of that as well but switching between the front, back or both pickups seems to make no difference in the level of hum and I figure if it was one of the humbuckers not doing it's job it should only have the hum when that pickup is selected.

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                • #9
                  Was it quieter before? You said the wiring is the same, but are the guitars the same? Same pickups? Same shielding?
                  Unless the guitars are the same, maybe a better question is 'why do some guitars hum more than others'.
                  "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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                  • #10
                    Did we ever get that audio clip?
                    Are you using the same cord with both guitars?
                    Have you tried the guitars in a different room as far from the room they're in now as possible?

                    Nothing about the tone circuit should affect hum. I'm interested also in g1's question. Did this guitar hum less before now?
                    "Take two placebos, works twice as well." Enzo

                    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

                    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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                    • #11
                      Again.. have you checked the bridge ground? If you don’t have a meter connect an alligator jumper from the ground plane to the bridge to test. Also.. those cheap selector switches can cause all manor of random evils.

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                      • #12
                        G1 -- It's the same as when I got it. Both guitars I got second hand for free from my work both in mostly working condition but requiring minor things, (new tuners on one, and a new selector switch on the other). Both guitars are different, ones an Ibanez and one an Epiphone, they do have different pickups and bridge styles so i'm sure there is a difference there. Both have basically no shielding, I plan on shielding both soon but am waiting until I can get a few things so I can do other stuff at the same time while I have them apart. I'm thinking I may just end up replacing both pots in both guitars as well while I have them apart since I'm not exactly sure the condition of them since I wasn't the original owner.

                        Chuck -- I'm trying to upload a clip to youtube but it's stuck at 95% still. I am using the same cord for both guitars, it's a nice big shielded cord I know that's not the problem. I have tried the guitar in other rooms without any real noticeable difference.

                        Olddawn -- The bridges and strings are both grounded albeit not neatly, they weren't grounded when I got the guitars and neither had a good spot I could find to ground them, so they have temporary wires right now, on the Epiphone its running from the bridge to the nut on the selector switch, and on the Ibanez its running from the metal plate on the back where the strings are fed through, to the cable jack nut. Not ideal but they work, I plan on running neater ones when I take them apart to shield them. Also the selector switch was like $12 from a local hardware store, It's actually a mains voltage switch so fairly heavy duty and definitely not the cheapest one I could have gotten, although i did burn it slightly soldering to it but i don't think that's causing me any issues.


                        Thanks again everyone for the help. I'm thinking i'm just going to replace the pots, switches, and jacks when I do the shielding and see how much off a difference that makes. Nothing's jumping out as obviously wrong with it so i'm thinking as G1 sort of said it may just be because they're different guitars, the one is just picking up more hum than the other.

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                        • #13
                          I would find out what's wrong before replacing everything.

                          Try disconnecting the tone pot wiring at the volume pot. Does it hum now? If so the problem isn't likely to be with the tone pot.

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                          • #14
                            Originally posted by DarkDragoon View Post
                            ...... on the Epiphone its running from the bridge to the nut on the selector switch......
                            That's fine if the selector switch body is grounded. Is it? It's best to just measure jack sleeve to bridge and make sure you have good grounds. Also, if you're bridge or tailpiece (whichever the ground wire goes to) is painted or powder coated, you'll need to scrape away some of the finish to get a good ground.
                            "Yeah, well, you know, that's just, like, your opinion, man."

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