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Impedance and Pickups Question

Discussion in 'Pickups & Electronics [BG]' started by gard0300, Feb 5, 2013.

  1. gard0300

    gard0300 Supporting Member

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    Does the resistance of a bass pickup affect the sound or just the output volume?
  2. steve_rolfeca

    steve_rolfeca Supporting Member

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    Pickup construction is something of a black art.

    Magnet type and placement, pole piece type and placement, height and width of coils, straight or scatter-wound, various noise-cancellation arrangements and a host of other factors affect tone and volume. Along with the number of winds of magnet wire, which is the main factor in the DC resistance of a pickup.

    About the only place where resistance numbers are really useful, is in pickup types where the other factors are tightly controlled, like repro vintage PAF humbuckers for guitar.

    In those situations, resistance does give you a general guide to tone and volume, with higher numbers tending to be louder, but darker-sounding.
  3. gard0300

    gard0300 Supporting Member

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    Higher numbers would be louder? I would have thought higher impedance numbers would be a lesser output as compared to a lower number.
  4. khutch

    khutch Praise Harp Supporting Member

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    There are so many variables in pickup construction that resistance measurements mean almost nothing. If every pickup ever made used the same gauge of wire, same coil dimensions, and the same strength magnets then the resistance reading would tell you the number of turns and that would tell you the output level. None of those three IFs are true though. All you can say is that generally a higher resistance means more turns and more output but there are many exceptions. Pickups are lightly loaded so within reason increasing resistance does not lower the output level because the increase in Voltage produced by the extra turns dominates. High resistance pickups will have a lower corner frequency with any given load capacitance so they do tend to sound darker. Keep in mind that any discussion of impedance which centers on resistance and ignores inductance is only going to be partially correct.

    Ken
  5. steve_rolfeca

    steve_rolfeca Supporting Member

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    First off, as Ken pointed out, higher numbers are ONLY relevant if everything else stays the same. In real-world applications related to bass pickups, the numbers don't mean much, in some cases even when looking at pickups made by the same manufacturer.

    Secondly, the numbers that you see quoted on spec sheets and in ad copy are for DC resistance, not impedance. We're connecting the pickup to a high-impedance voltage amplifier, not trying to drive a loudspeaker.

    It's got little to do with achieving the most efficient energy transfer, and everything to do with the voltage. In this situation, IF and ONLY IF everything else is equal, a coil with more turns will produce more output.
  6. steve_rolfeca

    steve_rolfeca Supporting Member

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    I'll go further, and say this:

    There's a lot of snake oil being sold when it comes to pickups. If you dig through the thousands of TB posts on the subject, it should quickly become obvious that you can find one or more fans for just about every pickup on the market.

    If the differences were easy to quantify, you wouldn't see all those contradictory posts about the best pickup for metal/country/whatever.

    This creates a huge problem for the people marketing pickups, and they have found that DC resistance numbers are one of the pieces of folklore that they can exploit to move you closer to a purchase decision. That's about all those numbers are good for.

    The truth is, that as long as it isn't microphonic, or has other mechanical or electrical faults, there's no such thing as a bad pickup. Pickup wizards like Bill Lawrence are able to design pickups that are clearly superior in terms of specific technical issues, but the fact that they can produce a technical improvement, doesn't guarantee that a given customer will be looking for it.

    To use a bad analogy, pickups are like salad dressing. Sometimes I want the ranch, and sometimes I want the balsamic. Meanwhile maybe the thought of balsamic makes you want to hurl.

    We're making a salad here, not striving for world peace, so there are no right and no wrong answers...
  7. Cadfael

    Cadfael

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    There is no DIRECT connection between impedance and output (as both others already wrote).

    But there is an INDIRECT connection.
    You can say that PUs with a higher impedance have a higher output as you can say that cars with more HP have a higher speed. In most cases this is true - as long as you don't include tractors or tanks.

    On a Jazz Bass (or Stratocaster +++) normally all PUs are made of the same material (Coil wire, magnets). But the nearer to the bridge, the higher is the impedance (to equalize the smaller getting amplitude of the strings).

    You can't compare the specs of different PUs and say that a 8.2k Ohms PU has a higher output than another 7.8k Ohms PU. But I would bat that a 12.4k Ohms PU has a higher output and more mid-punch than a 7.2k PU (for same position in the bass) ...
  8. SGD Lutherie

    SGD Lutherie Supporting Member

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    Disclosures:
    Owner, SGD Music Products
    To add tho these excellent answers; The more wire you wind on a pickup, the louder it gets, and after a certain point you will have an accentuated low end, the resonant peak will get lower into the upper mids, and then the treble rolls off.

    So, more turns of wire is louder, and the DC resistance is higher. It can be said that the impedance (AC resistance) has also increased, but that's more complicated. AC resistance increases with frequency, so if you take a measurement, it will be at 1,000 Hz, or what ever.

    Now something to bear in mind with DC resistance measurements is that thinner wire has a higher resistance per foot. So on something like a Jazz bass pickup, 8,000 turns of 42 gauge wire would be about 7,600 ohms (7.6k), while the same number of turns of 43 gauge wire would be about 9,500 ohms.

    The 9.5k pickup will not be louder, but it will sound different. Thinner wire has a tighter low end and more mids. Larger diameter wire has a rounder tone and less mids. If you wind the pickup up to 9.5k with 42 gauge wire (about 9,700 turns) it will be fatter and darker sounding, and louder than the 8,000 turn pickup. This is because it has more turns of wire on it.

    Other factors is the inductance of the pickup, which is a combination of things, such as the core of the coil (steel, alnico, ceramic, etc), the amount of wire and so on.

    Magnet strength and the type of magnet affect the tone, as does the geometry of the coil.

    Pickups are complicated little things because every little change affects something, and they all interact. And then at the same time they are simply some thin copper wire wrapped around a magnet. :D

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