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Reducing Locational Hum?

Discussion in 'Pickups & Electronics [BG]' started by Matthew_84, Nov 22, 2018.


  1. I picked up a new bass today (an Ibanez SRF705 "Portamento" fretless, with two Bartolini MK-1 split-coil magnetic pickups and piezo-pickups under the bridge saddles).

    It's great, but when I sit in front of my computer and turn up any of the magnetic MK-1 pickups and set the treble pot anywhere except for full-cut, I get a pretty nasty hum.

    I don't think it's a single coil hum because the hum is the same whether one pickup is on, or they are both at max. It also doesn't seem like a shielding issue because it doesn't matter if my hand is on or off the strings, bridge, or potentiometers.

    However, if I spin around in my chair and face in a certain direction, the hum pretty much completely goes away, even if I fully boost the treble pot.

    Is there anything I can do so that the hum is gone no matter which position I'm sitting?

    Thanks!
     
    Last edited: Nov 22, 2018
  2. Check for continuity between the bridge & the output jack.
    You'll need a Ohm meter or a multi-meter that can measure Ohms.

    Those MK1 pickups are quiet. I just had a SR600 for one night that had MK1 installed & it was very quiet, even in my noisy environment.
    The noise is probably being induced into the controls cavity & not the pickups.

    My G&L L-2000 was noisy in front of my computer, until I connected the foil on the controls cover to the cavity shielding.
     
    Matthew_84 likes this.
  3. Thanks KBD! I’ll check that out tonight.
     
    Killed_by_Death likes this.
  4. tektsu

    tektsu

    Nov 8, 2018
    My new SR375EF has exactly the same issue. I'll be checking out that continuity. Thanks!
     
    Matthew_84 likes this.
  5. @Killed_by_Death, so I have about 650 ohms (which I realize is too high) between the bridge/strings and the jack. I have about 1.2 k ohms (on average, these numbers bounce around a lot) on the pots.

    I opened up the control cavity and first was happy to see the back of the plate covered in foil tape, and the cavity painted black (which I assumed was conductive paint), but there's like 1.1 k ohms between the paint an inch apart, so it's just normal paint.

    That explains the problem... If you're going to paint it anyway, I don't understand why you wouldn't use conductive paint... Seems pretty silly on a $1300 (CAD) instrument.
     
  6. On my G&L L-2000 there was 500 Ohms between two points only 20mm apart, but the shielding worked.
    There shouldn't be so much resistance between your bridge & your output jack, however.

    Make sure the foil of the cover is contacting the shielding paint.
     
    Matthew_84 likes this.
  7. It’s only making contact by the pressure of the three screws holding the plate down. There isn’t a wire or anything to ensure a good connection. I’ll look into adding something. Thanks @Killed_by_Death, I appreciate it!

    I added a picture of the cavity if you or anyone else is interested.

    9E181D59-E21C-487A-86B0-391719008F26.
     
    Killed_by_Death likes this.

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