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Troubleshoot noise

Discussion in 'Pickups & Electronics [BG]' started by gravyboat, Sep 1, 2005.

  1. Hi, I need some help identifying the source of the noise my bass produces and how to get it fixed (or hopefully, fix it myself). Although I've been playing bass for years, I don't know much about the electronics, particularly active electronics.

    I've got a "prototype" Washburn T35 (made for NAMM or something equivalent) that has a Seymour Duncan SMB5 (MusicMan) pickup, which features a 3-band active EQ with boost/cut for low, mid, high, and the low EQ has a pull-pot for "slap contour". The construction quaility of the bass overall was not too impressive, so perhaps something was not wired properly? (the solder joints look OK).

    The problem is that the treble pot has a constant high hum to it; if I cut the treble all the way it's barely noticeable (but still there). When I boost it it's extremely loud. I've looked at the wiring, and there are a couple of unused wires that are taped at the ends.

    I took my bass to have it setup by a guitar tech and asked him to fix the problem (thinking he could just replace the treble pot). He suggested the problem may be with the preamp, but he wasn't sure, and couldn't find a wiring diagram for it.

    So, how can I go about identifying what the problem is (pup, preamp, pot)? Once identified, how could I fix it (I am fairly handy and can solder).

    Thanks for any suggestions.
  2. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    If the noise is being introduced through a fault in the wiring, like a ground loop, shielding issue, etc. It will typically alter when you touch the strings, bridges etc. Or behave differently in different locals, with different power sources, cables, that kind of thing.

    You have to at least consider the possibility that it is simply a noisy circuit. The way you describe it, it sounds like it may be just that. With an SD preamp and a MM style PU, it does make some sense.
  3. High hum? High as in pitch, or volume? Hum is usually low pitch, likely shielding /wiring problem, but could be bad preamp too, or merely miswired. Try seymour duncan website for wiring diagrams for their preamp.

    Does the hum change as you spin around? Sometimes I get hum facing north/south as opposed to east/west, for example. Has to do with being lined up with the source of the hum. That's being picked up by pickups or wiring. Good shielding would fix it being picked up by the wiring. Pickups could be harder to fix unless they can be wired in humbucking mode.

  4. Thanks for the replies; the 'high hum' is hard to describe -- sort of high-pitched, and turning the treble pot affects it.

    Something else that may help identify the problem is that is stops (or is significantly decreased) when I touch any of the control knobs, but not the strings. I'm thinking a ground problem?

    Unforunately, there are no wiring diagrams available at the SD website -- anyone know other resources?
  5. Le Basseur

    Le Basseur

    Mar 26, 2002
    What you describe here is a ground problem.Eventually,it can be solved in terms of a better ground & wiring layout but it'll remain the same if it's a bad PCB layout.
    The other issue is that,AFAIK,most Washburn onboards are hissy due to a poor components' quality.If you're satisfied with the woodenry and the PU's behaviour,simply replace the existing preamp with a brand one (Bartolini,Aguilar or anything fitting your needs and bill...just beware on the pots' config!).
    What happens to you was my main reason when I decided to buy a passive Taurus T24 wich I lately fitted with a homebrew preamp.Deadly quiet! :hyper:
    Good luck!
  6. Thanks all; I'll try the grounding and preamp options and report back.