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mysterious wire

Discussion in 'Luthier's Corner' started by Alex, Nov 11, 2005.


  1. I was snooping around inside my bass to under stand the electronics today. I opened the control cavity and then took off the pickguard on my bass. There were 3 wire leaving the control cavity. 2 left it in the direction of the pup, and one randomly exited toward the bridge. Once the pickguard was off I saw that the pup had 2 wires running from it (u have an OLP w/ an mm pup, and there are 2 pup volume controls, so it makes sense) So, this leads me to wonder: where does that other wire go? (It was the wire from the tone knob, if it makes a difference) Is it connected to the bridge for some reason. Help out a novice! :confused:
     
  2. I'm no expert on the subject either, but I would imagine it's probably the ground wire.
     
  3. LajoieT

    LajoieT I won't let your shadow be my shade...

    Oct 7, 2003
    Western Massachusetts
    Sounds like your bridge is grounded. Is it soldered to one of the pot posts or directly to the body of the pot itself?
     
  4. As the others have speculated, this would be for grounding the bridge.
     
  5. grounding the bridge???
     
  6. Frank Martin

    Frank Martin Bitten by the luthiery bug...

    Oct 8, 2001
    Budapest, Hungary, EU
    Let me ask, you have no idea how electronics work, right?
     
  7. I have a basic understanding. could you please explain it to me? :ninja:
     
  8. mahrous

    mahrous

    Aug 13, 2005
    Egypt
    most pickups have two wires (some have 4 or more). there is the live wire and there is the ground wire. the ground wire is where all the hum/buzz/noise go. you need to connect that ground wire to some metal (conductor) to suck all the hum.

    the two wires from the pickups (usually black and white. white is live and black is ground). the white is connected to the volume knobs, the black is soldered to the back of a pot. then you ground the pot to its back. then u connect the back of that pot to the second pot. ground the pot to its back. connect the back to the third pot. ground the pot to its back. then finally ground the last pot to its back and send a wire to the bridge (a nice metal conductor to suck all the buzz). also, you need ground your output jack too!

    what's said above is one way of doing things.
    many people dont like ground pots to their backs and prefer to ground directly to the bridge or similar grounds. i myself have used apartment keys, chains, coins and all sorts of different metals to ground to instead of the bridge. dont like drilling nasty holes back and forth in my body!
     
  9. ahhh, I totally get it now. ty so much.
     
  10. Hookus

    Hookus

    Oct 2, 2005
    Austin, TX

    Close, but not correct.

    The ground is part of a closed loop, which includes your strings, guitar cable, electronics, and amplifier. That ground from the bridge is there to put your strings, tuners, and bridge into the loop. Keys, coins, and the like will not do the trick. The ground is not where the hum goes, but rather is a place it will come from if it is bad, or if there is a ground loop problem. Which could be created by not grounding your bridge.

    Every single piece of metal that is not involved in the processing of tone should be connected together. This is the ground we speak of.
     
  11. LajoieT

    LajoieT I won't let your shadow be my shade...

    Oct 7, 2003
    Western Massachusetts
    I've actually heard many people mentioning that the bridge does not need to be grounded to reduce hum. I agree that it does help, and everything I've ever owned has been grounded, but they say that if the electronics are done right and shielded well the bridge (and by conduit, the strings) do not need to be grounded. Also if you aren't running wireless you have a very real potential of electric shocks if the grounding on the outlet your amp is plugged into is not the same as the grounding on something else (like a Mic or your guitarist's strings) and you touch them at the same time.
     
  12. That's why I have a receptacle tester in my gig bag.

    I've also heard it said that if the shielding is done correctly that the bridge ground is unnecessary, but I've never actually seen this case.

    I've seen schemes involving various capacitors between the bridge and ground to attempt to alleviate the risk of electric shock as well.
     
  13. but grounding it on anything else wouldn't do anything? Are you guys in a consensus that grounding is unneccessary? :eyebrow:
     
  14. I wouldn't say that's the consensus. Every bass I've seen has had reduced hum with a bridge ground.

    Also, what do you mean by grounding on anything else? Grounding the bridge does not mean that the bridge is the ground, rather it is connected to ground through the electronics.
     
  15. I have a P-bass copy with EMG active pups...no bridge ground necessary...no noise...

    what a bridge ground does is that it provides a path to ground for your strings...in return, the strings will then act as partial faraday cage around your pickups and help eliminate the pickups from picking up noise.
     
  16. mahrous

    mahrous

    Aug 13, 2005
    Egypt
    you have to ground your electronics and pickups or else you will hear nothing but HUM!

    i grounded to a spare apartment key and various metals such as coin (i think i said that above) rather than the bridge. the bridge is by no means grounded whatsoever and i have literally ZERO hum!

    try out different things till you get whats comfortable for you.
     
  17. Sorry, am I understanding this correctly, there is a potential of a shock if the bridge is grounded? :confused:
    Nearly got blown apart in the rain when I was a roadie, although I think we were running phantom power.
     
  18. nateo

    nateo Schubie Fan #1

    Mar 2, 2003
    Ottawa, Ontario
    Ha ha, I'm overeducated.

    Anyway, yes there's a chance you can get a shock with a grounded bridge. Certian faults in your bass or microphone amp or faults in the power systems they're plugged into can cause the grounds to be at different levels, allowing current to flow from one to the other. There have been a number of cases where singers burnt their lips because their strings weren't grounded the same as their microphone. I'm sure more severe things can happen, but I haven't heard of any deaths. On the other hand, the vast majority of instruments have grounded strings and most of us have never had a problem.

    Grounding the strings is, in my opinion, a redundant step in the reduction of hum (provided you've shielded your cavity and spent some time making your wiring pretty) with some unlikely but serious risks. Just about any cheap production bass you pick up will have a ground wire to the bridge in lieu of full cavity shielding or high quality electronics (high quality basses like a bit of redundancy to make sure there is no hum whatsoever). Grounding the strings not only allows the strings to act as a faraday cage in front of the pups, it also causes your body to act as a faraday cage across the back of the instrument. I believe this is why some people experience hum when they're not touching the strings on their instrument.

    Try a Google search on guitar wiring or grounding. I know the topic has been covered in great depth at various points on the internet.

    -Nate
     
  19. Are you saying that you are using the key as a point for a star ground? If so, this isn't what we are talking about. That isn't what the bridge ground is for.
     
  20. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    US-NY-NYC
    Close but not quite. AFAIK The strings are not providing the cage/shield to any significant degree. They are providing an electrical link to your body, which then acts as a shield across the entire back, and part of the front (by way of the plucking hand) of the bass.

    I haven't built a bass yet, but I will, and I definitely do not intend at this time to ground the bridge. I've been "bit" several times, and I don't feel like dying any time soon.

    This might be of interest.
    http://www.guitarnuts.com/technical/electrical/safety/index.php