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Shielding not stopping grounding issues - help me troubleshoot please...

Discussion in 'Pickups & Electronics [BG]' started by C-5KO, Aug 17, 2007.


  1. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    Hi guys,

    I'm in the middle of installing Nord DC's into my bass. After installing the first pickup, I found that I'm getting grounding hum (absent when touching strings, metal knobs, etc).

    I have checked continuity, and get a reading of 0.30 with my multimeter set on Rx10 (pretty much everywhere - shielding to shielding, shielding to jack, etc). Being a beginner at this, I'm guessing that anything but 0 is bad. What's the best way to go about isolating the problem? For some reason, I have a hunch that the problem lies in the shielding.
     
  2. Jonny B

    Jonny B

    Nov 5, 2006
    WI
    Are you grounded to the bridge?
     
  3. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    Yes. There's a ground wire coming from the bridge connected to the shielding.

    I feel that the shielding may be suspect because the grounds for the pickup and the bridge are connected in different places. Also, the shielding is tack soldered, but in many places... which I've seen avoided before.

    Edit:

    Just dropped the second pickup in, and it's out of phase... reversed the lead by accident! Whoops. Anyways, buzz is still there. I did plug in my bass with no pickup connected and the buzz was still there also (gone when I touch metal).
     
  4. kipsus

    kipsus Physicist

    Sep 18, 2005
    Vilnius, Lithuania
    0.3ohm is ok, I think shielding with conductive paint gives tens of ohms and it's still ok most of the time..
    Hum might be caused by a very EMI intensive devices like monitors, lamps etc. I had an old CRT monitor that made any bass hum when near, no matter what. Just that shielded humbuckers hummed less..
     
  5. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    Yes, where I practice is really bad for EMI, and the power is really dirty too.

    I always got the impression, that if the bass were properly shielded/grounded, all grounding hum should be eliminated. If I need to touch the strings for the hum to go away, doesn't that mean that the grounding is faulty, and I'm being used as a ground? Therefore if I improve the grounding in my bass, I won't be used as a ground when touching the strings.
     
  6. Rodent

    Rodent A Killer Pickup Lineā„¢ Commercial User

    Dec 20, 2004
    Upper Left Corner (Seattle)
    Player-Builder-Founder: Honey Badger Pickups & Regenerate Guitar Works
    is your soldering iron plugged into the same circuit as your amp?

    don't ask me how I know this can be the issue :rolleyes:

    all the best,

    R
     
  7. kipsus

    kipsus Physicist

    Sep 18, 2005
    Vilnius, Lithuania
    I think it's the grounding of the shielding. Try shielding pickup cavities and the pickups too if possible, then don't mix shield/signal grounds anywhere but output jack, use a good quality cable, reasonable gauge wires etc. Having star-ground scheme in any noise-prone circuit is a good idea
     
  8. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    I think you're right also. The fact that the pups were not connected, and I still was getting hum, I would assume means that it has something to do with just those components (shielding/ground). I'll have to check and see if the shield/signal grounds are mixed together. Is this the typical way to ground? not to mix shield/signal grounds?

    I've though about reworking the shielding too. I should connect the bridge ground to the control cavity shielding, the pup route shielding to the control cavity shielding, and the control cavity shielding to the jack.

    Then, take all signal grounds (pots, pups) and wire them to the jack also.

    I think I have either 18 or 22 wire...
     
  9. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    Hmm... actually no. The amp is connected to a different outlet (which is on a different circuit breaker).
     
  10. kipsus

    kipsus Physicist

    Sep 18, 2005
    Vilnius, Lithuania
    Have a look:
    http://www.talkbass.com/forum/showpost.php?p=4543725&postcount=38
    You can easily count 4 wires+cap soldered straight on the jack. I think only the bridge ground wire got soldered to the shield itself but hey - 0,5mm copper sheets have less resistance than any reasonably thick wire :cool:
     
  11. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada

    Thanks for the link.

    I made a quick trip to the local computer parts/junk store, and they had this neat roll of adhesive aluminium foil. It's sort of the size of a roll of duct tape. Anyways, this stuff is really easy to work with! One small problem though: I'm having the hardest time getting them to tack solder together. The solder doesn't want to transfer to the aluminium. Is there an easy way, or something I'm missing here in tack soldering?
     
  12. kipsus

    kipsus Physicist

    Sep 18, 2005
    Vilnius, Lithuania
    The easiest way is to use foil with conductive glue. Copper foil solders easily so that's ok too. And aluminum foil can be soldered but a special flux is needed. It's much more messy that way and I'm not sure about availability of that thing.
     
  13. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    Hmmm,

    I've isolated the shield/signal grounds from each other, and the hum is still there...

    Any suggestions as to what to try next? My guess would be to take the shielding out, and do it over...?
     

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