Additional base plate?

Discussion in 'Just Pickups' started by MadMaxie75, Oct 15, 2019.

  1. MadMaxie75

    MadMaxie75 TDPRI Member

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    I have a V-Mod bridge pup I would like to make slightly hotter and slightly warmer. The pup already has a base plate on it. Could I simply add another base plate to the existing one?
     
  2. Antigua Tele

    Antigua Tele Friend of Leo's

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    The one base plate that is already there barely makes any difference, a second would make no audible difference. In order for steel or ceramic parts to enhance on another magnetically, they need high permeability, which is the same as saying the parts require "low magnetic resistance". It's the same as with electricity, an insulator won't conduct well, if at all.

    AlNiCo pole pieces has a low permeability / high magnetic resistance (reluctance), so base plates don't do much for Fender pickups. The steel plate increases the inductance slightly, but barely enough to be audible. They were put there for shielding purposes, and possibly as a retainer for the AlNiCo poles, not to make the pickup hotter. They weren't intended for that purpose, and they don't really serve that purpose. It's just marketing. At the time, Leo Fender wanted clean head room, not distortion, so he would not have had hot pickups as an intended design goal. The best you can really do is raise the pickup closer to the strings, or experiment with putting low value caps across the pickup to give it a darker resonant peak.
     
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  3. MadMaxie75

    MadMaxie75 TDPRI Member

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    Thanks for the reply. So, for the uneducated, how do I put a cap 'across' the pickup? Is that essentially from the hot to ground? A bit of google suggests 1000-2000pf is a good range
     
  4. jvin248

    jvin248 Poster Extraordinaire

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    I cut Tele plate shapes out of house electrical octagon box covers. They are 1/8th inch thick and magnetic. I've found improvement with those. Thinner steel like from say a computer case (those old PCI knockouts are about perfect Strat pickup backers) are not thick enough to do anything, or have too much hysteresis loss. Many traditional Tele plates are copper clad and other materials meant for shielding against 60 cycle hum not magnetic flux. You'll want to get the steel plate to contact directly with the magnets for best success.

    Strat magnetic pole, looking at the side/end of a pickup.

    [​IMG]
    Tele magnetic pole with steel baseplate, see how the flux is 'reflected' back up for more output where the Strat just goes out the back of the guitar.
    [​IMG]
     
  5. Antigua Tele

    Antigua Tele Friend of Leo's

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    This is an two dimensional FEM model with unknown properties. It appears that there is uniform permeability in the modeled elements where as actual AlNiCo, especially AlNiCo 5, has a low permeability. If so, this will describe a steel poled pickup, but not an AlNiCo poled pickup. The relative peremability of AlNiCo is between 2 and 6 mu rel, where as steel has a nominally listed permeability of 4,000 mu rel, so an accurate depiction shouldn't show the field around the AlNiCo bending this much, under any circumstances.

    But lets say it was accurate, this FEM depiction also doesn't show any significant difference in flux density at the strings, the shades of blue are about the same at the corresponding elevations, therefore there is no reason to look at this model and conclude that it would increase the output. If you decide that the dark blue region is a millimeter higher, then that would imply you could get the same output by just raising the pickup a millimeter closer to the strings.

    The argument has always been that the base plate increases the inductance, which it does, but only slightly. It does this by interacting with the magnetic field of the coil, not the pole pieces.
     
    Last edited: Oct 15, 2019
  6. wabashslim

    wabashslim Tele-Holic

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    Yes, hot to ground. "Across" (usually) means "in parallel with".
    1000-2000pF is right in the ballpark. Results will vary depending on the pickups' inductance. I've tried anywhere from 680 pF to 3000 pF & in between by paralleling values.
    You can also try a resistor across the p'up instead of a capacitor. It tones down the top end a bit smoother. Try a value the same as whatever your volume pot is and go down from there.
     
    Last edited: Oct 15, 2019
  7. MadMaxie75

    MadMaxie75 TDPRI Member

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    Thank you kindly! Much appreciated
     
  8. Antigua Tele

    Antigua Tele Friend of Leo's

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    You would just put the cap across the hot and ground of the pickup. Know how when you turn the tone knob to zero he guitar sounds dark and has a "honk" tone? The idea is to create the same effect, but with a much smaller cap value. A tone control uses a 22 or 47nF cap, but to coerce darker sound from a pickup that is not muddy like a tone control, you would choose a cap value between 1nF and 6nF. Which value you prefer is a matter of taste, as are pickups in general. This isn't a hack either, it's electrically similar, if not equivalent to, what happens when a pickup is wound hotter.
     
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