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Volume output Issues on Seymour Duncan Pickups

Discussion in 'Pickups & Electronics [BG]' started by MCPLBASS, Dec 15, 2018.



    Dec 15, 2018
    I have exhausted myself trying to figure this out, and have brought my bass in to a local repair shop numerous times.

    I built a bass using a Music Man SMB 4A passive pickup and a SJB-3 pickup for the bridge (using 500k pots, 2V, 2T and 3 way switch). Both pickups sound great but they are not very loud compared to my P-bass.

    Using a multi-meter the SMB 4A gives me a reading of 7.5K and the SJB-3 gives a 14K reading. Together they come in around 10-11K. My P-bass has an output reading at 10.5K. The volume, however, is considerably different. The output is comparable when my built bass is at a level 7 on my amp and the P-bass at a level 2.

    There are times where the volume drops even more spontaneously and the tone gets kind of muddy.

    I should mention that the way it was wired, when both pickups are on, if you turn down one volume knob both pickup volumes decrease instead of independently.
    (It is wired in accordance with this diagram: Bass Instructions - Google Drive, with the music man pickup wired in series).

    Can this issue be fixed? Is there a way to test if volume is being lost through the pots or switch?
  2. eastcoasteddie


    Mar 24, 2006
    Does this happen spontaneously?

    Sounds like a definite wiring problem. Both pickups wired to one volume, or both in series with each other rather than parallel..


    Dec 15, 2018
    Each pickup is wired to its own volume and tone knob. Then to the switch, then to the jack. There are times when it seems okay but still not quite as loud as it should be.
  4. ctmullins

    ctmullins fueled by beer and coconut Gold Supporting Member

    Apr 18, 2008
    MS Gulf Coast
    I'm highly opinionated and extremely self-assured
    1. DC resistance is not a measure of pickup output (despite what many people imply). It is just one factor in pickup design.
    2. Spontaneous dropouts indicate faulty wiring, perhaps a bad solder joint or faulty switch.
    3. Your link actually contains several different diagrams, none of which match your verbal description. Got a better link?


    Dec 15, 2018
    1. I did not realize that. I've just always heard that the higher the DC resistance the hotter the pickup. Is there a way to test for output?
    2. Faulty wiring and bad solder joints I am assuming can be checked through visual inspection, but how can I test the quality of the switch?
    3. Sorry, I posted from my phone I thought it isolated the diagram I was copying. Here is a similar diagram. Both pickups were grounded to the back of their own respective volume pots. The SMB 4A is wired series. (Black to volume pot terminal, green and bare to ground, red and white together taped off). Capture.PNG
    ctmullins likes this.
  6. ctmullins

    ctmullins fueled by beer and coconut Gold Supporting Member

    Apr 18, 2008
    MS Gulf Coast
    I'm highly opinionated and extremely self-assured
    I do not know of any standardized test for pickup output. DiMarzio lists output in millivolts, but I don’t know if they publish their measurement methodology anywhere, and if they do, if it’s repeatable with other manufacturers’ pickups.

    A multimeter is really handy for situations like these. I would use one to check for continuity at various points in the circuit. Across the switch, it should read 0 (or very close) when the switch is closed, and “open” or “infinity” when it’s open (no connection). Any variation in resistance while the switch is closed is suspect. Jiggle it around while measuring, to test its robustness.

    Also use the multimeter to make sure that all grounds have (nearly) 0 ohms resistance to the barrel of the jack.

    That’s a pretty standard diagram for a Les Paul-style wiring. You can achieve independent volume controls by connecting the pickup hot to the center lug on the pot, and sending the output to the switch from the side lug (essentially swapping those two wires).
    MCPLBASS likes this.
  7. Laurent

    Laurent Supporting Member

    May 21, 2008
    Napa, California
    Your problem sound like bad wiring, bad solder or perhaps a bad component which is rare but happens.
    You might have to rewire the whole thing to find out. Tedious but generally effective.
    MCPLBASS likes this.


    Dec 15, 2018
    I have finally had a chance to open it up and take a look with a multi meter. Solder joints all look strong (pictures attached for reference). There's resistance from every point in the wiring. At some points the resistance jumps slightly (especially on the switch), but it never shows Infinite resistance. Volume output is still incredibly low (could the basswood be a factor?), And the tone won't stay consistent. IMG_20181229_221811. IMG_20181229_221840.

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