Difference between output in mV and DC resistance?

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by robyogi, Aug 2, 2006.


  1. robyogi

    robyogi Silver Supporting Member

    Messages:
    465
    Joined:
    May 26, 2005
    Location:
    Baltimore area
    If a pickup manufacturer gives both values - output in mV and DC resistance - what do the two values really explain? Not so much in electromagnetic terms, but more in terms of the way a pickup would sound or play. Is one the likelihood of the pickup to break-up versus stay clean, and the other the relative volume? Do either say anything about the tone? Does either value provide any meaningful info at all?
     
  2. Clorenzo

    Clorenzo Member

    Messages:
    1,940
    Joined:
    Jun 16, 2004
    Location:
    Munich / Madrid
    The output in mV gives you an idea of the pickup loudness compared to other pickups from the same manufacturer.

    The DC resistance tells you nothing, really. For a given magnet, pickup shape and wire gauge, higher DCR means more turns in the coils and hence higher output, but only if those other factors are the same, as in a manufacturer offering over / underwound versions for a particular model. But you can have a high DCR pickup with a weak magnet and a low DCR pickup with a strong magnet and the latter could well have higher output than the former. Higher DCR can also mean thinner wire, so it would actually be possible to have fewer turns with a higher DCR value, in which case, even with the same magnet, the high DCR pu could be quieter.

    There's one thing that makes DCR relevant and that's what happens when you combine pickups. There's an interesting, counterintuitive effect when you have for example your typical combo with a PAF in the neck position and a high output, high DCR humbucker in the bridge position (like the usual Jazz / JB combo, 8k / 16k). When both are selected, the PAF contributes a lot more to the overall tone than the hot humbucker, the tone being much closer to the PAF on its own than to the hot HB on its own. The reason is mutual loading: the low DCR PAF is loading (in a sense "shortcircuiting") the hot HB a lot more than the other way round. Interestingly, if you have separate volume controls and turn EITHER of them down a bit, the contribution from the hot HB increases, because the resistance of the vol. pot sort of "isolates" both pu's and prevents this loading effect. This is also responsible sometimes for the lack of "quack" of certain pu combinations in a Strat where there's a big mis-match between their DCR's.
     
  3. rooster

    rooster Member

    Messages:
    2,123
    Joined:
    Mar 9, 2005
    Location:
    Arizona
    Well, sort of. As the post one more up the page mentioned, output and tone have much more to do with the construction of the pickup. The inductance, which varies with frequency, is more of a determiner of output and tone than anything else. The inductance is a function of the windings and the magnetic field, and we use XL =2(pi)fL to determine the inductive reactance. There will also be capacitive reactance which will interact with the inductance and create various resonant peaks.

    Usually the rule of thumb is that the higher the DC resistance, the more output, but not necessarily so.

    rooster.
     
  4. rooster

    rooster Member

    Messages:
    2,123
    Joined:
    Mar 9, 2005
    Location:
    Arizona
    Exactly. Which is why some pickups read very high on DC resistance on an ohmmeter and put out what would be heard as "normal" volume levels, some sound muddy when would with high DC resistance, but some sound great. For a good primer on how the pickup characteristics interact, the bill lawrence (real BL, not BL USA) website has a nice "pickupology" section that kind of details it.

    The bottom line is that some people make good pickups, some don't. And, you cannot determine the tone by price and rarity, although many try to do that.

    rooster.
     
  5. rooster

    rooster Member

    Messages:
    2,123
    Joined:
    Mar 9, 2005
    Location:
    Arizona
    Yes. Couldn't have said it better, unless maybe we added some unnecessary profanity for the metal crowd.

    rooster.
     

Share This Page