1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  
     
    TalkBass.com has been uniting the low end since 1998.  Join us! :)

Can/should I wire a capacitor straight to ground?

Discussion in 'Pickups & Electronics [BG]' started by fourstringbliss, Jun 7, 2011.


  1. fourstringbliss

    fourstringbliss Supporting Member

    Oct 5, 2003
    Puyallup, WA
    I'm wiring up my bass in passive and have a question about capacitors. All of the wiring diagrams I have seen show the capacitor on the tone pot being soldered to the back of the pot. I'm star grounding when I do my wiring - could I just connect the capacitor straight to cavity ground rather than the back of the pot?
     
  2. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Yes, in the normal config, the back of the pot is connected to ground, so you can connect the cap straight to gnd. I think it's just traditional to solder to the pot because that reduces the chances of a leg of the cap getting broken as the wiring gets moved around.
     
  3. madmatt

    madmatt

    Apr 28, 2009
    Yes. You could.
     
  4. Why are you star grounding?

    It makes no difference how you ground, so long as you have 0 Ohm continuity between all ground points. Don't buy into that ground loop NONSENSE.
     
  5. fourstringbliss

    fourstringbliss Supporting Member

    Oct 5, 2003
    Puyallup, WA
    I star ground mainly because it keeps thing simple for me. I don't like soldering to the back of pots because I have burned up pots before trying to get a cap lead to solder to the back of it. I'd much rather connect to a wire from the cavity ground.

    Thanks for the info!
     
  6. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    You should ground the pot cans though, and you should have a ground wire connected between the pots. The cavity ground is shielding, and not a ground plane. Don't use that for ground.

    Star grounding is not easier because you are ganging all those ground wires to one location. You are also adding unnecessary wire length to the ground wires.

    Just scrape p the top of the pot a little and melt some solder on it. Then you can solder your cap or ground wire as quickly as you solder to the pot's lugs. You don't burn them up, do you?

    Also, instead of bending up a pot's lug and soldering it to the case, use a piece of bare wire. That's what I do.
     
  7. Tracebassplayer

    Tracebassplayer Sometimes Darkness Can Show You The Light.

    Dec 15, 2000
    Portland, OR
    +1

    This is "why" you do it that way.

    Wire in an audio circuit is like an antenna for your radio... it picks up RF signals and can pass them to your amp. That's why the cavity and you guitar cables are shielded (to help keep stray RF out) and the pots are grounded (to shunt RF signals to ground where they disappear to the earth).
    If you're getting the pots too hot do like SGD Lutherie said, scrape the pot shiny where you are going to solder. It will make it "take" the solder faster and have a much better electrical connection.... or you're using to hot of an iron.

    Bending the lug more than 3 or 4 times generally will crack it and you will lose connectivity or break it off completely.
     
  8. fourstringbliss

    fourstringbliss Supporting Member

    Oct 5, 2003
    Puyallup, WA
    Thanks for the suggestions, David! These are excellent!
     
  9. If the pots are actually getting burned, your iron is not hot enough. Your iron should be hot enough to quickly make a solder joint without having to hold it to the pot casing for too long.

    If you can't get the solder to stick, you haven't roughed up the pot casing properly.

    +1.
    It is a terrible idea to simply bend a lug back and solder it to the casing. While it eliminates the need for two solder joints, it's difficult to ever desolder the connection to remove the casing later on, if you are unable to securely mount the pot to something while holding the iron with one hand and bending the lug with the other.
     
  10. fourstringbliss

    fourstringbliss Supporting Member

    Oct 5, 2003
    Puyallup, WA
    I never knew about roughing up the casing - that would definitely help.
     
  11. fourstringbliss

    fourstringbliss Supporting Member

    Oct 5, 2003
    Puyallup, WA
    I've wired up my jazz bass using this wiring diagram:

    [​IMG]

    and the tone control is acting like a master volume instead of a tone control. The only differences between the wiring diagram and how I wired it is that all of my ground wires lead to the same spot connected to the cavity shield (which is where the jack and bridge ground wires go as well) and that the capacitor isn't soldered to the back of the tone pot but is connected to cavity ground. The pot shells are all grounded. Both volume controls work like they should.

    I'm using these Bourns audio taper pots and an Orange Drop cap. Any ideas why this might be happening?
     
  12. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    Wow, that diagram is plagiarized from Seymour Duncan!

    Standard Jazz Bass Wiring Diagram

    Why do you have your ground wires going to the cavity shield? That's not good wiring practice. You have a lot of extra wire in there now too.

    It sounds to me like your cap is shorting out on the wrong side to ground, i.e., on the side that goes to the pot. If you have no shorts, then you might have a bad cap.

    Check that none of the lugs from the tone pot, or any other part of the cap are touching ground. Only the other end of the cap should be. Sometimes it helps to put some electrical tape under the pot's terminals so they don't touch the shielding or control plate.

    Try lifting the cap from ground and see if the problem goes away. If it does, try a new cap and don't over heat it.
     
  13. fourstringbliss

    fourstringbliss Supporting Member

    Oct 5, 2003
    Puyallup, WA
    My soldering iron is only a 15v and doesn't get hot enough to effectively solder anything to the back of a pot. I do have too much wire in the control cavity, but I've figured out a way of eliminating some of that without a better soldering iron.

    I thought that the capacitor was supposed to go to ground? It's soldered to the back of the tone pot, but the jack ground and bridge wire are all connected there, right? Doesn't that take the cap to ground?

    Wait, the tone control cap lug shouldn't touch ground, right? I have a wire connecting that lug to the pot shell, which is also connected to ground. This is shorting out the capacitor, huh?
     
  14. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    You have the tone control wired up like a volume control. The tone control lugs should only connect to the signal on one side, and the cap on the other, and then the opposite side of the cap goes to ground.

    None of the tone control lugs should go to ground.

    Look at the diagram you posted. problem solved. :D

    try this one:

    0032.
     
  15. fourstringbliss

    fourstringbliss Supporting Member

    Oct 5, 2003
    Puyallup, WA
    Thanks! I kinda wondered about that wiring diagram. I'm going to get a better soldering iron and start over.
     
  16. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    Just cut that jumper to ground and you are all set.
     
  17. fourstringbliss

    fourstringbliss Supporting Member

    Oct 5, 2003
    Puyallup, WA
    Cut the wire that goes from the capacitor to ground?
     
  18. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    You wrote:

    Disconnect the wire from the lug to the pot shell on the tone pot. It shouldn't be there.
     
  19. fourstringbliss

    fourstringbliss Supporting Member

    Oct 5, 2003
    Puyallup, WA
    Yup. I'll ground the pot shell differently. Thanks!
     
  20. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    Just don't connect any of the lugs on the tone pot to ground. That doesn't ground the pot shell, that grounds the lug! That's why it's turning your signal down to nothing. Your signal is going to ground.

    Disconnect that one wire and you should be good to go.
     

Share This Page