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P pickups do I have to shield them? comon! really?

Discussion in 'Pickups & Electronics [BG]' started by kpolki, Aug 7, 2012.


  1. kpolki

    kpolki

    Jul 7, 2011
    On to my second build and I am installing some nordstrand P pickups np5. The pre amp is a ACG pre amp.
    When it comes to electronics Im not that clued up so take it easy on me.
    After I installed them there was a major buzz, (note: no strings on at this stage) I thought P pickups were supposed to be Hum cancelling? I had already shielded the cavity and grounded that and the pre to the output jack. So next I did an expieriment, I removed and roughly wrapped the the pickups in silver foil (around the outside of them) and then grounded across to one of the control knobs. Good that removed the the bad buzzing, almost dead quiet now. So its a shielding problem right? or have I missed something. As I said I thought P pickups were hum cancelling? Do I really have to go to the trouble of trying to somehow shield these pickups now? comon! really? I wouldnt know where to start. Please tell me Im a dumb ass and missed or did something wrong.
    I know this is probably not enough info so fire away.
     
  2. kesh

    kesh

    Jul 9, 2012
    Brighton, England
    maybe they messed up the wiring and didn't put the coils out of phase.
     
  3. bassbenj

    bassbenj

    Aug 11, 2009
    There are TWO kinds of hum! The first kind (electric) is the kind that goes away or gets less when you touch ground (the strings). It is eliminated by shielding.

    The other type of hum is magnetic and does NOT go way when you touch ground. This is the kind of hum that hum-cancelling pickups (like a P-bass or a J-bass with both bridge and neck pickups on full) eliminate.

    You have to deal with BOTH kinds of hum. Shielding the cavity is a good start, but you ALSO have to shield the pickup cavity and the WIRES going to the pickups. All this will pickup hum!

    Ideal would be to enclose the pickups in a sealed metal enclosure to shield them, but this isn't practical because the tops have to stick out. So what you need to do is shield the bottom and sides of the pickup cavity PLUS shield the wires going to it (I often make a copper foil tube I shove through the wire hole and solder to shield on both ends). Also you should have copper foil on the back of the pickguard that acts like a partial "lid" to the pickup cavity. That foil also needs to be grounded. usually you run it over to a pickguard mounting screw and you run the cavity foil up to the same screw so when you screw down the pickguard it makes contact. (or you could just solder a wire to it and be sure)

    On the other hand if you've got hum that does NOT go away when you touch ground but changes when you rotate the bass around, then your hum-cancelling isn't working right and you'd look for reversed wiring on the pickup coils.
     
  4. kesh

    kesh

    Jul 9, 2012
    Brighton, England
    one of my beefs with many pickups is them not using screened cable. especially ones taking the authentic vintage thing pointlessly too far.
     
  5. Schmorgy

    Schmorgy

    Jul 2, 2012
    Canada
    So based on the post above (My squier P bass is having hum issues on one of the pickups) I should be able to fix my hum with more shielding? Whenever I get hum, by touching the strings it instantly goes away. Should I just shield with tin foil as per the instructions above?
     
  6. kpolki

    kpolki

    Jul 7, 2011
    Ok, yes the hum/ buzz does go away when I touch ground (controls) so it is a shielding problem I guess. shielding the cavity is easy enough but what about the pickups themselves , I dont have a pickgaurd I can sheild so wont interference enter through the top of the pickup ? . I suppose I could line the inside of the pickup covers with foil or copper but does this alter the tone ? do I have to put a break in it to stop a complete loop as Ive read that this acts like another winding ? Does everyone else have this problem with these pickups and have to shield them ?
    these pickups better be worth it as I didnt have this problem with my bart single coils on my first build.
     
  7. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    Did you have the ACG preamp in your first build? In my experience, the ACG has the capability of boosting the highs quite a lot, and it can be really picky about grounding and shielding on the pickups.
     
  8. Well first off, I assume you have checked the cheap stuff, your wiring, and made sure everything is OK, maybe bypass the circuitry and hotwire the pickup straight to the jack and the hum is still there. Then you could go 3 ways:

    1. Send the pickups back to have them make sure they're up to snuff, or ask them what values you should see on your multimeter, and ask about how they're wound, if they do hum a bit or if they're supposed to be dead silent.

    2. If you feel like messing with it, and the problem is that the coils don't match enough to humbuck, you could try the Bill Lawrence ones for 4/5/6 that use 2 identical coils at http://wildepickups.com/Bass_Pickups.html

    3. If the pickup tests out OK or they tell you you have to accept some hum, pay once, cry once. The Ilich large coil noise canceling system will work http://www.ilitchelectronics.com/largecoilnoisecancelingsystem.htm
     
  9. kpolki

    kpolki

    Jul 7, 2011
    Yeah, good idea I will hook directly to the jack and see what happens.
    The hum/buzz I was getting was way unacceptable so hooking directly to the jack should tell me if its a pre amp/ wiring prob or faulty pickups,
    if Im still getting unacceptable amounts of noise after going drectly to the jack then its a pickup problem right ? and I should send them back ? After all P pickups should be hum cancelling, I dont mind a bit of hiss but not the offensive hum/ buzz I was getting.
     
  10. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    +1

    All pickups should be internally shielded. The fact that they aren't is because it wasn't needed 50 years ago. Our environment is noisier now as there are a lot more electronic devices around. Pickups should also use shielded cable.
     
  11. kpolki

    kpolki

    Jul 7, 2011
    I wish I had known this before I purchased the pickups. My barts were half the price and obviously came shielded. So Im a bit surprised the manufactorer dosent shield them or at least inform the customer that they need shielding.
    Can anyone give me a step by step guide on how to internally sheild pickups. I cant find any info out there.
    Please help!
     

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