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Grounding on back of pots

Discussion in 'Pickups & Electronics [BG]' started by Alowishus, May 4, 2005.


  1. Alowishus

    Alowishus

    Feb 28, 2005
    Why shouldnt I do this? Is there any downside to grounding on the back of potentiometers? Should I just send everything directly down to the ground line?
     
  2. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    It's not that you shouldn't do this, as it is generally the standard practice.

    But it's not optimal practice for two reasons.

    First, it's better for each component to have an individual path to a common ground point. This prevents ground loops and keeps things quieter.

    Second, and this is especially important with stacked pots and pots that contain push/pull switches, if you don't solder the pot casing, the inside of the pot won't overheat. This can easily happen with the pots listed above or any pot with plastic parts inside.

    Note that doing individual ground wires costs maybe 5 cents' worth more wire and takes maybe 10 minutes more per instrument. For an individual doing the work on their own guitar, that's nothing and the results are well worth it. For a manufacturer, 10 minutes and a few cents more per instrument adds up, so they don't bother to do it.
     
  3. SirPoonga

    SirPoonga

    Jan 18, 2005
    Ground loops occur when there is multi paths to ground and you get feedback. I'd think the chance of a ground loop is higher if things aren't daisy chained. So with more wires going to ground there's more paths to take. With daisy chaining there's only one path to ground, there's no other ground paths to feedback on.

    You get this problem alot with subwoofers in home theater systems. Both the amp and the sub have a three prong plug two two gorund paths. You get the ground loop hum from the sub because electricity from the amp found less resistance going out to the sub, through the woofer. The usual cure for this is either get a 3 prong to 2 prong convertor for the sub or ground the amp better. Then, essentially, the sub's ground is daisy chained with the amp's ground via the ground of the cable between them, one path for the electricity to go.

    However, that's for high end electronics. for the pots and such in your bass it probably wouldn't be a problem so it really doesn't make a difference. At this scale grounding the pots individually to the output jack or grounding to pot case is essentially the same thing. So you really don't need to worry about it, do whatever way you like and are comfortable with.

    Also with ground to pot casing the tiny bit of static generated from handling the plastic knobs has some plce to go :)
    Plus then if you shielded your electronics cavity it will automatically be grounded.
    Plus to the electophobe less wires usually means less resistance, though that tiny bit doesn't effect anything of that scale.

    To a rookie solderer this would be a problem. But if you solder correctly this shouldn't happen. Your iron would not be on the pot long enough to heat it up. Takes less than half a second to solder
    But yeah, I could see how one would avoid it in that case.
    The bad thing about grounding to pot casing, then running a wire between each casing (like my friend's les paul, but that uses cable sheilding for ground so this won't be a problem) is if the ground wire inbetween componants breaks/goes bad everything that grounded to that won't work. While doing them individually only the parts that has a failed ground won't work. So maybe the wire between the tone pot's cap and ground came loose, say faulty soldering. You loose tone control but still have volume.

    So, really, there's pros and cons for each way.
     
  4. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    Except that's not the case. With each component individually grounded, each component only has one path to ground. Daisy chaining, particularly in a Jazz where the control plate also passes ground, can lead to ground loops.
     
  5. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    In Les Pauls and similar instruments I remove the pots and use heavy copper shielding in the cavity so once the pots are screwed down, they are grounded together.

    And I'm perfectly capable of soldering to a pot case, and have done it when a pickup only allows that option (like a Kinman). But in general I avoid daisy chaining and try to separate shield from signal negative except at one common point.

    Pot ground lug = signal negative.

    Pot casing = shield.
     
  6. Alowishus

    Alowishus

    Feb 28, 2005
    My sx has a brown wire running to the bridge of the bass that serves as a ground. I realy dont want to remove the bridge in order to get to the ground point. My sx is currently grounded in a daisy chain fashion and it seems fine to me, but if you realy recommend against it Lyle then could I just send everything along that one brown ground wire?
     
  7. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    No, the bridge is not the ground point. The bridge is grounded via that wire to the ground point. The ground point should be in the control cavity so you can access it.

    I'm not saying that daisy chaining grounds is bad. I'm saying it's not optimal. When doing a new circuit from the ground up, I do recommend star grounding. But if you're just modifying an existing circuit and you aren't 100% sure what you're doing, then leave things as they are.
     
  8. Alowishus

    Alowishus

    Feb 28, 2005
    I guess, Ill just install a grounding lug in the control cavity and then ground each individual component to it. Also, since the brown wire runs to the back of one of the pots im going to remove, could I just solder it to the grounding lug i'm going to install? Thanks for your help lyle and sirpoonga, please bear with me :) .

    PS. I'm following your Volume-Blend-Tone with a 3PDT switch for series/parallel diagram lyle and I just wanted to thank you for making it. :D
     
  9. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    Yes, just solder the bridge wire to the common ground lug. Always glad to share what I've learned.
     
  10. MAGUS®

    MAGUS®

    Dec 23, 2004
    UK
    What is STAR grounding ?

    Is that a universal term or American ?
     
  11. SirPoonga

    SirPoonga

    Jan 18, 2005
    That's an interesting way of grounding. I suppose then everything touching the shielding is grounded, including output jack if it is in the cavity too. Would make for a clean looking cavity, and allow more room if you want to add a preamp or a battery for your own active electronics.
     
  12. SirPoonga

    SirPoonga

    Jan 18, 2005
    No, it shouldn't. Ground loops are caused because the signal found a path of least resistance to ground that goes through a componant causing feedback. Wires add resistance. Individual wire could induce ground loops. Each componant has it's own "ground" so to speak, simular to how a gorund loop hum occurs in the home theater example.
    What could happen is say one pot's ground wire is longer than another but it connected to the other pot. Maybe the signal finds that it is less resistance to go back through the signal wire to the other pot and out that pot's ground, being there is short enough ground wire and signal wire that there is a significant difference in resistance.


    Now daisy chaining (assuming not your jazz bass situation) the least resistance will most likely be directly to the pot's casing then follow the daisy chain to output jack, instead of through another componant.

    With the jazz bass situation (or cavity shielding) one could use that common metal as a ground plate. ground everything to that, don't run gorund wires from one componant to the next. Then you shouldn't have ground loops.

    For a passive bass either way probably wouldn't be a problem. Introducing power into the system could change things though.

    It would be easier for me to draw a picture to explain but I don't have a drawing program with me right now :(
     
  13. On my '67 Thunderbird, I put copper foil in the entire cavity and both pickup cavities, with a wire from each pickup cavity to the control cavity. The ground wire from the bridge was soldered directly to the foil. The wire that typically is needed to hook all the pots together was not needed at all! Just the 'hots' to make it all work. Talk about a clean and simple wiring job! And, no hum, no loops, and clean looking.
     
  14. Alowishus

    Alowishus

    Feb 28, 2005
    Out of curiosity, why does the bridge have to be grounded?
     
  15. mrelwood

    mrelwood

    Dec 15, 2004
    Finland
    'Cos You have to be grounded! :)

    No, seriously, the player is a part of the grounding in a guitar/bass with passive pickups.

    The basic idea of a pickup picking up vibration, is to have a grounded object vibrating in the magnetic field. Although, some sound will come out if the strings are not grounded.

    Using EMG's or other active pickups, (PICKUPS, not preamps!) string grounding is not needed.


    -Aki.
     
  16. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    String grounding is also not needed if the instrument is fully shielded.
     
  17. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    I don't think you're arguing against what I've actually said. In my examples (see my pictorial in the pickups FAQ) there can be only one path to ground from each component. All components have 0 resistance to ground. Star grounding is well-established good practice.
     
  18. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    FWIW:

    in regards to shielding, what worked well for me was to simply run 5/8" strips of shielding between the pots to eliminate the ground wires with an accesible strip to solder the strip to the jack wire ground and you need no ground wires to pots at all. Alternative to soldering to the strip you can solder a ring connector to the bridge/jack ground (whatever) and simply screw them down through the shielding. You can check all ground connections with a meter to verify good grounds.

    Really cleans up the cavity and considerably reduces trouble shooting when a problem arises cause the problem is typically a grounding issue. Also eliminates the problem encountered with blends and stacks already mentioned.

    The pots have to get pretty hot to solder ground leads to pot backs which not only creates potential damage to the pot but is the biggest challenge for the novice in soldering. And nothing looks more amatuer than some bourgeoisie slagged up potback.

    I found shielding the entire cavity time consuming, a pain, and of little or no benefit. Shielding the entire cavity also creates optimal opportunity for shorts. I threw strips of electrical tape below all pot lugs and along the wall anywhere a hot pot lug was close to contact since any hot lead that contacts the shielding will go to ground.