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Ground noise

Discussion in 'Pickups & Electronics [BG]' started by CrackBass, Nov 17, 2006.


  1. CrackBass

    CrackBass

    Aug 10, 2004
    huntsville,AL
    hey guys, you know how some basses buzz when you take your hands off the strings and break the ground? well i use elixir stings and that sound will not go away unless i touch the bridge or the knobs. i guess the coating kinda insulates me from making a ground. when i ground the bass by making contact it is dead quiet but as i play there is an annoying hum. is there anyway around this? or do i need some uncoated strings? the bass is a jazz deluxe with the fender noisless pickups and an audere preamp.

    thanks
     
  2. Try totally shileding the control cavity?

    That usually removed all (nearly) noise.
     
  3. Audere

    Audere Supporting Member Commercial User

    Apr 7, 2005
    South Beach, OR
    Owner: Audere Audio
    What is happening is your body is moving up and down (in voltage) at the power line frequency - this gets coupled to the pickups.

    When you touch the uncoated strings you are grounded. The string coating will insulate you...

    Shielding in the pickup cavity can help - this is often more effective than shielding the control cavity which is probably already shielded. This is probably the next logical step.

    But any solution which removes or drains the charge from your body will also work.

    I know of a studio where they made a conductive floor (this is standard technique for electronics assembly areas) and grounded the chairs etc. They also at times used some electronic assembly static protection grounding wrist straps as ankle grounding straps. Maybe a bit over the top but it worked…
     
  4. CrackBass

    CrackBass

    Aug 10, 2004
    huntsville,AL
    well i fixed it. i took off the plate and got a jumper wire. the i methodically grounded every thing i could think might need grounding while the bass was plugged in and listened to see if i could get the noise to stop. (of course i wasn't grounding the bass by touching it) i have no idea what possesed me to ground the pickup mounting screws on the neck pickup but i'll be damned if that didn't shut the noise down completely. it has me completely vexed, yet thrilled that the buzz is gone. i soldered the ground to the ground on the output jack and it's a done deal. absolute silence whether touching the bass or not.

    moral of the story, make sure you ground the mounting screws of the neck pickup on your jazz bass. why? i have no idea.
     
  5. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    FWIW:

    that is pretty strange. Even stranger was someone posted not long ago asking about grounding pups screws - seems it preceded this thread but if not I guess they read this post.

    I was going to say with those pups and a pre there should be no noise but its all relative. So many things cause noise from ground issues alone that the Twilight Zone stuff Audere was mentioning fits right in. Old Fenders frequently have cracks in the shielding on the pg that cause strange variable sounds when touched. It's always sumpthin.
     
  6. Audere

    Audere Supporting Member Commercial User

    Apr 7, 2005
    South Beach, OR
    Owner: Audere Audio
    Interesting that you think capacitance coupling from the human body to the grid voltage is in the Twilight Zone.

    It is trivial to demonstrate with any oscilloscope that your body has an imposed voltage on it so you might ask someone for a demo.
    FYI virtually everyone uses it to make sure they know their scope channel is active...

    If this pickup has a bracket on the bottom and that is connected to the adjustment screw (common on lots of guitar pickups but uncommon on jazz bass pickups which are normally mounted to only a plastic cover) then by grounding the screw he grounded the bracket which created a shield from the noise on his body. Or maybe the cavity had a shield in it already which was not connected to ground before he used the screw as the connection point.
     
  7. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    That wasn't a cut/mock/criticism/choose your term - just a reflection of my response to the technical side of life.

    I'm a plug and play, trial and error, no tech, focus on the end product no capability of comprehending the anatomy of the that sound kind of guy. Hard sciences were never my forte' but I'm glad there's people like yourself - otherwise guess I'd be playing acoustic bass in some mariachi band.

    So for me, "capacitance coupling from the human body to the grid voltage" is in the Twilight Zone. You may as well try and teach a turtle calculus.

    I do understand the part about the screw in effect completing the ground circuit under those conditions. That I assumed was the case given the results obtained but your last post explains why that may be so - and that's something this simple mind will retain for a while.

    Actually not a lot of electrical engineers in this forum though. So what may strike you as very trivial may not be so for the individual(s) you're communicating to.
     

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