DC resistance reading - J-Bass pups

Discussion in 'Pickups & Electronics [BG]' started by El Tedesco, Dec 20, 2012.

  1. El Tedesco

    El Tedesco

    Dec 20, 2012
    Hello All,

    I finally signed up here and like to get straight to the question I have.
    I started changing pickups on my J-Bass. As I was taking readings on all my other Basses, I noticed that, unlike readings on guitar pups, the DC resistance seems to read pretty much exactly 1/2 the value of it is supposed to be.

    Ex: 3.25 Kohms on a low output pup that's supposed to have around 6.5 Kohms. Same on another, reads 4.2 Kohms, while it should be 8.4 Kohms.

    The meter seems to be doing just fine and guitar pups read exactly as they are supposed to.

    Is there something I am missing? I can't wrap my brain around this.

    Now my intro.

    Playing Bass since around 35 years. I'm not a Pro, but some nice R 'n' B.
    This Forum helped me many times, when searching for answers on all kinds of topics.

    I like to thank everybody here, who engages in providing answers to the many questions people have in regards to Bass playing, instruments and other details.
  2. Are you measuring the pickups together? The formula for parallel resistance is R[SUB]Total[/SUB]=1/([1/R[SUB]1[/SUB]]+[1/R[SUB]2[/SUB]]+...[1/R[SUB]n[/SUB]]), thus, if two pickups of approximately equal DCR are parallel, the total resistance will be approximately half.

    Or it could be that you are wiring coils of a series humbucker in parallel, when the DCR is specified per-coil rather than the series total, but that's unlikely.
  3. El Tedesco

    El Tedesco

    Dec 20, 2012
    Hello Line6man,

    the formula makes me dizzy :eyebrow:

    No, the pups are not installed. Even installed, I measure one at a time directly on the wire.

    My procedure for measuring is the same as always, but the result is as described.

    So, I'm just not getting what's going on here ...:crying:
  4. Stealth


    Feb 5, 2008
    Zagreb, Croatia
    El Tedesco, are you measuring the original or the replacement models? What model are they? Maybe they're humbucker pickups like DiMarzio Area Js or similar, which actually have two coils inside one casing, and which may be internally wired in parallel.
  5. El Tedesco

    El Tedesco

    Dec 20, 2012
    They are all single coils.
    American Std J-Bass Alnico V
    3.6 Neck, 3.6 Bridge
    MIM Std J-Bass pickup Ceramic
    5.0 Kohm Neck, 5.2 Kohm Brigde
    MEC Dynamic Correction (Warwick Corvette)
    9.3 Kohm on both with the blend knob fully open on either Neck or Bridge These seem to be the only correct reading, although I have no reference on their value, they are hot, ergo could be 18 kohm each.

    I also have a custom set that is per winder's specs in the low 8's for the Neck & high 8's for the Bridge, both read about 1/2 value (4's) :confused:

    Somebody help me solve this mistery! :ninja:
  6. Stone Soup

    Stone Soup

    Dec 3, 2012
    I didn't know it's possible test a pickup while it's in the circuit. hmmm...
  7. El Tedesco

    El Tedesco

    Dec 20, 2012
    I measure at the wire. It doesn't matter whether they are installed or not. If you have braided cloth push back insulation just push it back and put your meter pins directly on the exposed wire.

    But that's not the issue here.

    It's that my readings show consistently 1/2 the value of what their DC resistance is. I measured them about a dozen times each set. Changed the battery in the meter. Meter is calibrated @ 0.00. Exact same result.
    Unlike my guitar pups, which show exactly as indicated by the manufacturer. Same measuring method.

    If somebody can tell what I am doing wrong :help: ...or is there a reason for it? I wouldn't think so.

    I could just let it go, since it matters very little. I am just stunned with the situation and was wondering if anybody has an answer to this.
  8. Yes it does. If the pickups are wired into the circuit, the resistance of the pots decreases the total resistance, following the parallel resistance formula I posted above. You need to measure them while they are disconnected from the circuit, unless you want to do the math.
  9. El Tedesco

    El Tedesco

    Dec 20, 2012
    You might be right, I don't want to argue this, although, I am getting the same readings of resistance on every solder point, even at the out put jack. That applies for pups in the circuit.

    Again, my question referred to a different objective.
  10. megafiddle


    May 25, 2011
    Don't know if I understand exactly how you are measuring, but if they are in the circuit,
    and connected in parallel (both selected) you can't measure them individually simply by
    moving the probes. If they are wired together (through a selector switch, for example),
    it doesn't matter where you place the probes. You will be reading both in that case.
    And the reading will be around half of each.
  11. This is not true. Soloing a pickup by removing one pickup from the circuit with a pickup selector switch, grounded volume pot, or grounded blend pot, removes the other pickup from the circuit, allowing only the resistance of the pots to apply parallel to the pickup you want to measure. If you have a bass with two volumes, the resistance of the pots can be measured directly by turning both volumes down. In the case of pickup selectors and blend pots, you would have to guess at the pot resistance, based on rated values and tolerances that are known. The resistance of the pots does not have a significant effect on the total resistance when measuring a pickup's DCR, however, so the measure is not critical.
  12. bassbenj


    Aug 11, 2009
    Readings at all solder points won't matter. If you want to measure the DC resistance of a pickup you MUST disconnect at least ONE of the wires from the bass. Testing when connected is only good for finding shorts and things like that.

    This rule applies to testing all kinds of parts. When they are in the circuit there are just too many unknown things to deal with. Whether or not they are "installed" in the bass (as in screwed into their cavities) makes no difference if the wires are still hooked up.
  13. megafiddle


    May 25, 2011
    That is basically what I meant.

    This statement:

    "I am getting the same readings of resistance on every solder point, even at the out put jack."

    indicates that the two pickups just might be connected to each other,
    through a switch and/or volumes at '10'.
  14. Stone Soup

    Stone Soup

    Dec 3, 2012
    No, he IS right. No argument at all.
  15. El Tedesco

    El Tedesco

    Dec 20, 2012
    It's this thing about internet forums, where righteousness is presented and re-enforced even if it's besides the point.
  16. El Tedesco

    El Tedesco

    Dec 20, 2012
    I think that's incorrect. Your reading might be affected by other components, but you still get a reading of the pup's DC resistance.
  17. El Tedesco

    El Tedesco

    Dec 20, 2012
    I think this is confirmative and comes closest to answering the objective question. For installed pups, anyways.

    Here is what I observed, J-Bass 2 Volume, 1 Tone
    Measure the wire at the volume solder point with both pots fully open results in each pup reading 1/2 it's value.
    As soon as I close one volume pot, the one that remains open doubles the value.
    This makes sense.

    Still, my readings on uninstalled pups are exactly 1/2 value on each.
    There's got to be something about J-Bass pups being designed, unlike other pups. At least that's what it's hinting at.
  18. SGD Lutherie

    SGD Lutherie Inactive Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    Those figures seem too low.
  19. As you have noted, placing two pickups of similar DCR in parallel decreases the total DCR to about one-half. When you measured both pickups in parallel while they were wired up, did the DCR drop to approximately one-quarter of the rating for one pickup? Since you have described that the DCR of each pickup is one-half its rating when measured alone, the total resistance should drop to approximately one-quarter of the rating, if both pickups have an approximately equal DCR, when they are wired up in parallel in the circuit.

    Righteousness? What was beside the point?

    What you said was:
    The first paragraph of this statement is the reason for the third paragraph, in this context. That being said, it is very difficult to understand what exactly you are doing, because without further clarification on your methods of measuring the DCR, the behavior you have described either points to you having improperly measured the DCR of a coil in a parallel circuit, with the results supporting the physics of a parallel circuit, or you have pickups that defy the physics in an extreme way. The former is much more plausible than the latter.

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