Buzz persists after thorough shielding

Discussion in 'Pickups & Electronics [BG]' started by Renegade Riff, May 17, 2020.

  1. Renegade Riff

    Renegade Riff

    May 10, 2020
    Guys, help please. This is my circuit. I had buzz that went away when I placed my hands on the strings. Therefore, it was a shielding problem. I shielded the cavity thoroughly (as you can see). The same buzz persists. I thought it was the jack touching the shielding, producing a ground loop. I put tape around the parts that made contact. Problem got worse! I am out of ideas. I see the "star grounding" is on the tone, not volume pot. Is that it? I was worried that if the shielding touched the pots, I would get a ground loop, so I placed white insulating tape beneath them (and kept the black ground cable from volume to tone pot). Did I screw up? Any help much appreciated my circuit.jpg
  2. tzohn


    Apr 26, 2015
    Maybe the blanks around the pots? Is it copper tape with conductive adhesive? Or you should try shielding the pup covers too. Why did you cut so many tiny pieces instead of just covering the pickguard with 2-3 stripes and then just cut the pot holes?

    Edit: just realized this is white tape, not blanks.
  3. Renegade Riff

    Renegade Riff

    May 10, 2020
    Well, I'm sort of learning as I go along. I had read that the only thing to avoid in grounding was "ground loops", so I was worried that if the pots touched the shielding a ground loop would happen. So I tried to keep the bottom parts of the pots blank... later realised that an insulating tape would be even better, so I added that on top.

    Yes, the copper tape is adhesive on both sides.
  4. Doner Designs

    Doner Designs Steve Doner Gold Supporting Member

    Jun 2, 2012
    Metro Chicago Area
    Doner Designs is an alias for Steve Doner
    I have never had a "ground loop" cause a problem in a bass.

    The main thing is to make sure that everything is well grounded including bridge, jack body, pot bodies and pickup pole pieces.
  5. tzohn


    Apr 26, 2015
    Is it copper tape specifically for guitar shielding? The pots are grounded anyway with the soldered black wire so try covering the whole pickguard with copper tape and leave no blanks around the pot holes
  6. Gilmourisgod


    Jun 23, 2014
    Cape Cod MA
    Buy a cheap multimeter with a “beep” feature for continuity. Dirt cheap at HF or Amazon. Put the probes on various points to see if the copper tape ground is continuous, no beep = a break in the ground path. You can tack solder pieces of copper together at the seams, you shouldn’t have to if the the foil is conductive adhesive, but sometimes it doesn’t work, which is why it’s better to use wide foil and as few pieces as practical. Do you have the bridge ground wire in good contact with the bridge, and is it wired to ground? Check all the solder connections. Re-flow any that look dull or loose.
  7. dwizum


    Dec 21, 2018
    It looks like you were very thorough in the control cavity. What about up by the pickups? Does the shielding extend all through the routing under both pickups? What kind of pickups are they? Do they buzz in all positions/combinations? If they're typical single coil jazz pickups, you will inevitably have some buzz with either pickup solo'd. I'm assuming p bass from the pickguard but it's worth pointing out.

    Also - what's your environment like? My music room is a section of a finished basement. My wife has her home gym equipment at the other end. We put a really bright dimmable LED light fixture above her section. If that light is on, ALL of my basses have at least some buzz, even the well shielded active humbucker basses. That light is like a disturbance in the force. Obi wan can probably feel it. Try going around your house and turning lights off or checking for other contributing factors. On my more sensitive basses, some brands of LED bulb will make them buzz and others won't (so I just hoard the "good" bulbs for use downstairs!)

    And what equipment are you playing through? If you've got pedals, preamps, power amps, etc and they're plugged into different circuits in your home wiring, you may have a real ground loop, not just a tiny one in your bass.

    You said the problem got worse when you insulated the jack from the copper shielding. Double check the solder joints on the ground wire running to the jack and the rest of the ground path from shielding to jack. The shielding and the jack should already be connected (through the ground wire from your tone pot to the shielding, and from the tone pot to the jack). Changing the connection directly between the shielding and the jack and having that cause a change in the buzz may mean that there's a problem in the "real" connection between the shielding and the jack.

    And at the end of the day, you could just try swapping the jack. I've had more bad jacks (even from good brand names) than I care to count. Sometimes they're bad out of the box, other times they're only bad with certain cables, or they go bad after a year or two... it can be frustrating to troubleshoot a bad ground only to discover it's a jack that has a poor connection even though it visually looks fine or is brand new. Also try a different cable! Sometimes it's the simple things.
    janesaid likes this.
  8. You have tape around where the jack goes through the pickguard. Is there any place where the copper tape is connected to ground? If not, the shielding isn’t doing anything and can, in fact, act as an antenna. Also, what Gilmour said, make sure there is continuity through all of the shielding. It looks like you have some overlapping from the cavity in the body to the top so it will make contact with what’s on the pickguard but make sure you have some kind of connection there also.
    scuzzy likes this.
  9. Killed_by_Death

    Killed_by_Death Snaggletooth Inactive

    Take all that insulating tape OFF!
    You can't have a Ground-Loop in a single device, that happens when you have more than one device connected with different potentials to Ground.
  10. Renegade Riff

    Renegade Riff

    May 10, 2020
    Wow... thanks a *lot* for taking an interest. Let me go by parts:
    - it is indeed a P-bass and pickups are as thoroughly shielded as everything else
    - yes, the environment. True what you say, but I compared the P-bass with how my telecaster sounds (same amp, same room). And the Tele is silent.
    - the equipment is just an amp but as I say, with he Tele it's silent
    - I will definitely have a closer look at the jack. And as you say, maybe it's just a faulty jack... could well be. Something to investigate.
    All the best, will let you know, many thanks!
    Thegrandwazoo likes this.
  11. Renegade Riff

    Renegade Riff

    May 10, 2020
    Yup, shielding is connected to ground. But I guess I could connect and additional cable from the cavity to ground and not rely on the connections with the pickguard. Something to consider... thanks.
  12. Renegade Riff

    Renegade Riff

    May 10, 2020
    It sounds like you know a lot more about electronics than me, so I will do as you say! It's the only thing that I did which I came up with by myself. I haven't seen this anywhere else. So makes sense to take it off. Thanks.
  13. Renegade Riff

    Renegade Riff

    May 10, 2020
    Yup, I have good ground contact between bridge and the circuit. I take note that sometimes the adhesive does not work... will look out for this. And looks like I need a multimeter too ;-)
    Thegrandwazoo and Gilmourisgod like this.
  14. Renegade Riff

    Renegade Riff

    May 10, 2020
    I don't know if specific to guitars, but it is definitely conductive on both sides. I will do as you say and just cover the whole pickguard with the tape. Thanks.
  15. Renegade Riff

    Renegade Riff

    May 10, 2020
    OK, well that's good. I'll forget about the whole ground loop thing. Nobody seems to be bothered by it. Thanks.
  16. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism

    Contrary to what Stew-Mac tells you, that isn't a thing. Copper foil tape is all the same, whether you use it for a guitar or stained glass. You can also use aluminum foil tape for ducting or just kitchen aluminum foil.

    I am assuming that this issue is limited to one bass and isn't coming through the power or another piece of gear. If not, test the bass elsewhere. Other than that, I don't have much to add here, lots of good advice in this thread.
  17. tzohn


    Apr 26, 2015
    It seemed initially he did not understand the "conductive" part so that was another way to ask him if the product he used has conductive adhesive. I don't buy from StewMac anyway but what you mean is that all adhesives are conductive?
  18. Hectobar


    Nov 10, 2016
    +1,000. Had a p bass I couldn't tame. Shielded the whole thing and still buzzed like a 1972 clock radio. Turns out it was led lights. Yep. Music stuff is upstairs over the kitchen w led lights. Lights in kitchen on, buzzes like hell. Lights off silent. I soldered, taped, resoldered, cussed, banged head, etc.

    Could be outside source of interference.
    projectapollo likes this.
  19. Killed_by_Death

    Killed_by_Death Snaggletooth Inactive

    False, shielding tape has conductive adhesive.
    It is cheaper to get shielding tape from somewhere besides Stew-Mac.
    paco facile likes this.
  20. T_Bone_TL


    Jan 10, 2013
    SW VT
    Since it goes away when you touch the strings, I'm going to be very suspicious of your bridge ground, even though you say it's "in good contact." Others have already cleared up the "ground loop" red herring.

    Other possibility depending on your level of experience is that you have achieved a cold solder joint somewhere, and what appears to be connected is actually insulated by a layer of rosin flux. The (need not be expensive/fancy) multimeter you now have on your shopping list would help you to find that.

    Personally, I hate the "standard guitar practice" of soldering to the back of pots - they are not designed for that, and it's difficult to do well (there's no mechanical connection), as well as possible to damage them by overheating them while trying to do that. You can get star washers with solder tabs that connect mechanically to the shaft. But I'm very much in the enginerd minority on that subject.
    Last edited: May 17, 2020
    mcnach, 16notes and Thegrandwazoo like this.