New Pots = More Hum

Discussion in 'Pickups & Electronics [BG]' started by johnson79, Feb 25, 2013.


  1. johnson79

    johnson79

    Joined:
    Jan 8, 2010
    Location:
    East Petersburg PA
    I put some new pots in my passive PJ bass yesterday. First things first, it is not shielded, so I am used to hum.

    After a few hiccups I got it working and it sounds great. The only issue is there is more hum than before. I am running a volume for each, no tone control, with 500k pots.

    Just curious if, other than shielding, I may need to look at the wiring again to reduce the hum. Shielding is my next project, but for now it was pots and a new jack.

    Any thoughts are appreciated.

    And I can post some pics later if that would help, but it's the standard PJ set up.
  2. Cadfael

    Cadfael

    Joined:
    Jan 4, 2013
    Location:
    Germany, EU
    Did you have 250k pots before?

    500k pots give more high frequencies - but also more humming.
    Did you have a tone pot before? Removing the tone pot totally also gives more high frequencies ...

    The "right" lug is soldered to ground as it should?

    The P PU alone doesn't hum?
  3. johnson79

    johnson79

    Joined:
    Jan 8, 2010
    Location:
    East Petersburg PA
    The bass did have 500k previously. The right lugs on both are connected to the back of the pots. I had removed the tone pot from the chain a few weeks ago and didn't notice
    a change.

    Could it be the new, higher quality pots are just making it more noticeable?

    I really need to get it shielded, so this may be enough motivation to do it soon.
  4. BogeyBass

    BogeyBass

    Joined:
    Sep 14, 2010
    Only other thing i could think of is when you rewired it.

    Is you might have cold solder connections to ground, or the ground wire going to the bridge got pulled out slightly and is no longer touching the bridge.

    you do have regular hum reduction when you touch the strings and bridge right. if not then you need to reset the bridge wire.

    also the humbucker pair as said, solo should have less hum, then if you bring up the single coil volume. Hum will increase no way around it. Sometimes wiring can cause more hum and improving wiring can have a bigger effect on hum reduction than shielding can.
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  6. johnson79

    johnson79

    Joined:
    Jan 8, 2010
    Location:
    East Petersburg PA
    It is reduced when I touch the strings and such, so it seems to be grounded. I'll check my pot ground solders. The P seems ok.

    I'll digg around some more tonight.
  7. Cadfael

    Cadfael

    Joined:
    Jan 4, 2013
    Location:
    Germany, EU
    Maybe the new pots are not worse but better?!
    Becoming worse might mean, that the new pots enable things to be heared that weren't heared before ...

    Guitar players won't use bass cabs as bass cabs make thing hearalbe that guitar cabs don't reproduce (high or low frequencies). The Fender Bassman has only become a famous guitar amp, because it was such a lousy bass amp ...

    It might be a wiring fault - but it might also be a too good "reproduction" of what really is ...
  8. johnson79

    johnson79

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    Jan 8, 2010
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  9. johnson79

    johnson79

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    Jan 8, 2010
    Location:
    East Petersburg PA
    Well, I re-soldered the back of the pots and now I do have a ground issue. I checked the bridge ground, and it was fine. Back to square one I guess.
  10. wvbass

    wvbass Supporting Member

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    Mar 1, 2004
    Maybe you should star ground it. :bag:
  11. parsons

    parsons

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    Feb 22, 2008
    Location:
    Maryland
    You should have next to 0 hum with both pickups on full. Every PJ I own is wired to two volumes and doesn't hum when both pickups are full.
  12. uOpt

    uOpt Supporting Member

    Joined:
    Jul 21, 2008
    Location:
    Boston, MA, USA
    The shielding protects against electrostatic buzz. It does nothing about the 50/60 Hz cycle hum that is induced into single coil pickups magnetically. You have a Jazz pickup, it's gonna give you 50/60 Hz hum unless it's a hum-canceling J design.

    If you have more hum now then there's a bunch of possibilities:
    - not grounding the pot's case
    - using more amounts of unshielded wire in an unshielded cavity than before
    - use of unshielded wire between pickups and cavity where it was shielded before
    - selective memory
    - by coincidence the amount of interference is now more

    Unshielded wire in unshielded parts of the bass pickups up a lot of that random buzz.
  13. Matthew_84

    Matthew_84

    Joined:
    Nov 7, 2010
    Location:
    Toronto, ON, Canada
    Then you had a humcancelling J pickup. If a PJ bass has a single coil Jazz pickup, then it will hum as soon as as it's turned up at all, whether the P pickup is on or not. The split P pickup hum cancels itself, it does not effect the single coil Jazz one bit.

    I'm thinking it's just the new pots are clearer and you can hear it more. This happened with a jazz I installed new pots in a couple of months ago.
  14. walterw

    walterw Supportive Fender Gold Supporting Member

    Joined:
    Feb 20, 2009
    agreed, PJs all hum unless the J pickup is itself a humbucker.
  15. Bassamatic

    Bassamatic keepin' the beat since the 60's Supporting Member

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    Location:
    Studio City, SoCal, USA
    Just fyi- The "quality" of the pot does not affect the quality of the sound. Only the value affects the sound. A cheap pot sounds exactly the same as a good one, just won't last as long.
  16. johnson79

    johnson79

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    Jan 8, 2010
    Location:
    East Petersburg PA
    I'm assuming it's my lack of soldering skills. I need to just get the shielding tape and a wiring kit and start from scratch.

    At the time of my first post it was just 60hz hum, which was not audible when I touched the strings/bridge. Now, after attempting to clean up what I assumed was a cold solder joint I have a constant buzz which means I have a bad ground connection somewhere. After trying to fix it twice it is still there. Could I have fried the pots?

    Should I have continuity between all grounded points? I do, which is why I can't seem to pinpoint my issue.

    Thanks for the brainstorming guys. I'm getting super frustrated...
  17. johnson79

    johnson79

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    I bought Alphas for $1.75 on Amazon. The old mini pots must have been totally shot.
  18. SGD Lutherie

    SGD Lutherie Banned

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    If it's the buzzing that goes away when you touch the strings, then the grounds in the bass are fine. But the grounds where the amp is plugged into might not be. Check the outlets. Shielding can help that too.

    If it's the hum you get when the J is soloed, that's something different. That's from single coil pickups.

    The high pitched buzz and the low pitched hum are two different things.
  19. uOpt

    uOpt Supporting Member

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    Jul 21, 2008
    Location:
    Boston, MA, USA
    No, it's either or. If you screwed up this round of soldering and the bass was fine before there is no reason going with the shielding tape. You fix the soldering you are back to old hum levels. if they were fine before they are fine now.

    And again, the shielding tape only helps against the electrostatic random buzz, not against the 50/60 Hz cycle hum from the AC power in the house.

    Can you describe a bit more what kind of pickups with what kind of wires you have there?

    So you did no changes except new pots? Did you change from one control layout to another?

    You can fry a pot easily. You should test with some crocodile clips.
  20. johnson79

    johnson79

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    Jan 8, 2010
    Location:
    East Petersburg PA
    The issue now is the low pitched hum. The single coil buzz was the original issue, but in typical fashion I have made things worse. Now, the issue is the low pitched hum, which is not relieved by touching a string.
  21. johnson79

    johnson79

    Joined:
    Jan 8, 2010
    Location:
    East Petersburg PA
    I have a set of PJ Quarter Pounders. I used the SD diagram for standard PJ, which is the same as it was already wired from the factory. I used 22 g unshielded wire for everything.

    I'll check my pots and confirm they are still OK.

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