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A problem with pickups, preamp, shielding or...?

Discussion in 'Pickups & Electronics [BG]' started by SoVeryTired, Jul 19, 2012.


  1. SoVeryTired

    SoVeryTired Endorsing nothing, recommending much

    Jul 2, 2011
    Milton Keynes, UK
    I'm a definite non-expert when it comes to matters electronic so please forgive me if my problem is common and/or stupid.

    Background: I play a MTD Kingston Heir 5 (MM-J, 3-band active, all stock electronics) in a church band. No amp, just through my pedal board straight to DI, with IEMs for monitoring. The usual sort of lighting you'd expect in a large hall (500-seater) but no excessive electrical equipment around - no amps on stage at all.

    Problem: I've noticed that I'm picking up the house sound through my bass. I noticed this tonight when an iPod was being played through the speakers but not in monitors. I was getting it in monitors through my bass. When I turned the volume up on the bass, the music got louder. When I turned the blend towards the neck single-coil, louder still. Boost the treble? Even louder. It may be that I've got the bass soloud in my ears that I'm hearing a problem that no-one else will notice, but I'm concerned that this is happening at all.

    I've opened the bass with no idea what I was actually looking for. The control cavity seems tidy, no loose connections and it seems to be pained with what I presume is shielding paint.

    Question: any idea what's most likely to cause this sort of problem? The only tests I can easily run are plugging direct rather than through my pedal board (I'm sure I've tried this before with no difference but will check again) or trying a different lead. After that I'm left with wiring, pickups or pre-amp as the possible problems.

    Thoughts? Any help greatfully received!
     
  2. 96tbird

    96tbird PLEASE STAND BY Supporting Member

    I'm no expert, but pickups are microphones. Feedback is merely pickups picking up the sound from speakers, an active circuit will boost the effect. Pickup windings will also begin to vibrate, just like your undamped strings, if not potted. Just my thoughts, I may be all wet, but I wouldn't worry as long as it doesn't squeal. Is also find out if those pups are potted and do it if they aren't.
     
  3. SoVeryTired

    SoVeryTired Endorsing nothing, recommending much

    Jul 2, 2011
    Milton Keynes, UK
    Okay, next question - how to tell if pups are potted? Is it just a case of removing the covers and looking to see if the windings are visible or covered in wax?

    If not, potting them sounds like a job that's probably beyond my abilities. I can set the bass up but don't know one end of a soldering iron from the other!
     
  4. 96tbird

    96tbird PLEASE STAND BY Supporting Member

    Pull them out. If the covers come off , scrape your fingernail on the inner surfaces of the bobbin plate to see if there's any wax; don't scrape the wire. If the covers are epoxied on, they will usually be epoxy impregnated (potted).

    Potting is easy, but you have to know how to solder to take them out and put them back in.
     
  5. SoVeryTired

    SoVeryTired Endorsing nothing, recommending much

    Jul 2, 2011
    Milton Keynes, UK
    I'll check them out. I have a feeling that the pickups may not be that great. Has anyone else had this sort of problem and solved it?
     
  6. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    If you lightly tap your fingers on the pickup, can you hear it?

    With any pickups, if you put small speakers like earbuds close to the pickups, you will hear the audio. This is normal, and is cause by magnetic inductance.

    But the pickup shouldn't be picking up the house sound.
     
  7. SoVeryTired

    SoVeryTired Endorsing nothing, recommending much

    Jul 2, 2011
    Milton Keynes, UK
    I'll have to check. If I can hear the tapping, what would that mean?
     
  8. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    That would mean the pickup are microphonic and need potting.

    Most pickups will make some sound when you tap them, but you don't want it to be loud.

    This is why many pickup makers use epoxy to make the pickup a solid mass. It eliminates microphonic issues.
     
  9. SoVeryTired

    SoVeryTired Endorsing nothing, recommending much

    Jul 2, 2011
    Milton Keynes, UK
    Right. My mission when I get home is to: see if I can get under the covers my pickups; then plug it in and tap the pickups.
     
  10. SoVeryTired

    SoVeryTired Endorsing nothing, recommending much

    Jul 2, 2011
    Milton Keynes, UK
    Pickups checked - sealed units so I can't see inside but, on that basis, presumed potted.

    Plugged in with headphones and all controls maxed. Tapping with fingertip: not audible. Tapping hard with fingernail: audible.

    And the diagnosis is...?
     
  11. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    OK, so your pickups are not sensing the music because of vibrations.

    If you put small speakers near them, like ear buds, they will indeed pick up that sound because of magnetic inductance. So that's one source of the problem. But you said the music isn't going into your IEMs.

    Another thing might just be the board. You said you are going into a DI first? When you change the control on the bass does it change the music as it comes through the mains, or you just hear it in your monitors?
     
  12. SoVeryTired

    SoVeryTired Endorsing nothing, recommending much

    Jul 2, 2011
    Milton Keynes, UK
    Changing the controls changes the music - that's how I could tell the music was coming through the pickups. Volume, pickup blend and EQ all affect the music in the earbuds, with neck single coil, treble boost producing the strongest signal.
     
  13. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    Changes the music out the mains?

    Are you plugged into a DI box, or direct in the board?

    Where is the iPod plugged into?
     
  14. I suspect the onboard electronics are picking up the signal as airborne electrical noise. Better shielding(metal tape)may help.
    Next time at church, see if changing the direction you and the bass are facing makes a difference. If so, there it is.
     
  15. SoVeryTired

    SoVeryTired Endorsing nothing, recommending much

    Jul 2, 2011
    Milton Keynes, UK
    Sorry, I wasn't clear.

    Changes the music in my ears.

    The i-Pod was plugged into the desk at the back of the hall. I was plugged into a DI rack unit at the rear of the stage. The i-Pod was playing through the house speakers only but was coming through my ears through my bass pickups (as proved, I think, by the sound of the i-pod in my ears being turned on and off with my bass's volume pot).

    Hopefully that's clearer, if no closer to an explanation!
     
  16. SoVeryTired

    SoVeryTired Endorsing nothing, recommending much

    Jul 2, 2011
    Milton Keynes, UK
    I didn't check facing different directions - that's something else to try.
     
  17. SoVeryTired

    SoVeryTired Endorsing nothing, recommending much

    Jul 2, 2011
    Milton Keynes, UK
    I didn't get a chance to replicate the problem on Sunday - Thursday will be next chance to check it out.
     
  18. SoVeryTired

    SoVeryTired Endorsing nothing, recommending much

    Jul 2, 2011
    Milton Keynes, UK
    Okay, I think I've isolated the problem now. I was getting the same issue yesterday so enlisted the help of one of our PA guys who's a fellow bassist.

    We first of all made sure there was an identifiable problem. House speakers turned up with recorded music playing, bass on a stand on stage with all the controls maxed (to exaggerate the effect), listening to the channel with noise-cancelling headphones through the mixing desk. Any other channel: silence. Bass channel isolated through headphones: microphone-like playback of what was coming through the house speakers.

    Next, eliminate the other possible candidates. Different leads? No change. Take tuner pedal out and plug direct? No change. Unplug acoustic guitar and plug into that channel? No change. Change pickup blend from neck to 50-50? No change. Change pickup blend to solo'd bridge? Almost completely gone.

    So, my conlcusion from this (correct me if I'm wrong) is that my neck pickup is microphonic, and the tiny amount of microphonic effect when just selecting the bridge pickup is possibly due to the way the blend pot works, i.e. it still lets a tiny amount of neck signal through.

    So next steps, I think, are potting the pickup if it's not potted already or replacing the neck pickup.
     
  19. SoVeryTired

    SoVeryTired Endorsing nothing, recommending much

    Jul 2, 2011
    Milton Keynes, UK
    And I've had confirmation that the pickups aren't potted and are glued in to the cases.
     

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