Best resistance value for a Spin-a-Split trim pot?

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by heretic, Jul 4, 2013.


  1. heretic

    heretic Member

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    I 'm installing a Spin-a-Split pot on my guitar. I'm intending this pot to be "parked" in one sweet spot position, so I'm planning to use a trim pot that'll live in the guitar's controls cavity. (There's also an unused DPDT push-pull switch which I'll use to engage the tap).

    What value pot should I use? I had a 500k spin-a-split pot before, which worked just fine, but are higher/lower values better?

    The HB in question has a DC resistance of 7kΩ .

    :confused:

    Thanks for your help!
     
  2. fakeox

    fakeox Member

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  3. walterw

    walterw Gold Supporting Member

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    for an external knob i'd go with 500k; any lower and you'll be ever so slightly attenuating one coil even with it on "10".

    now if it's gonna always be at least partially "on" and hidden inside the cavity, you might as well go with a 250k; it'll be easier to dial it in to that "just so" setting, as the sweep will be less jumpy.

    i think you also might want to go with linear taper, to have finer control at the top of its turn where a little change makes a big difference.
     
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  4. m-m-m

    m-m-m Member

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    Based on my recent experience I would agree with that. I recently rewired the tone pot in an HH 's' style guitar I have - the change was very abrupt at at the full-up side of the pot (in my case full up was just one coil). If I were to try it again I would use a 250K linear taper pot. (I'm assuming that the pot I used was a 500k audio taper. Isn't that what's normally used in HH guitars for the tone pot?)

    FYI, I ended up going single volume and a petrucci wired 3-way blade switch for that guitar. The middle position gives me the inner coils from both HBs in parallel. Tons of quack. I was floored. YMMV.
     
  5. heretic

    heretic Member

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    Thanks Walter and m-m-m ! I was thinking along the same lines - a smaller value will give me more precision in finding the sweet spot, while the switch will let me take the pot out of the circuit, so I'm not worried about the value being too low.

    As for the taper, I'm looking at those small 3-legged footstool-looking trim pots that need a flathead screwdriver to operate. Are those usually linear taper?
     
  6. heretic

    heretic Member

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    So, after trying a bunch of trim pots of various resistance, I found that:

    - pots in the 100k range are way too high, the values jump too much...
    - a 5k linear pot would be perfect, but the surplus parts store didn't have one .

    So I settled on a linear 10k pot with 10 detent notches. The sweet spot seems to be in the 2-3 kOhm range, which seems to align with resistor values PRS uses in the DGT.

    Hope this helps someone...thanks again, for all the feedback.
     
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  7. walterw

    walterw Gold Supporting Member

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    so it's wired as an actual potentiometer? in, out and ground? i'm surprised 10k does anything more than almost totally kill the one coil.

    or is it just wired as a rheostat (in and out only), strictly creating in-line series resistance?
     
  8. heretic

    heretic Member

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    The latter - only using 2 out of 3 connectors :)

    I hate having a dangling pot held by 2 wires wrapped in electrical tape inside the cavity, but..out of sight, out of mind :roll
     
  9. m-m-m

    m-m-m Member

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    Interesting. Thank for sharing heretic. Glad u found something that worked.
     
  10. walterw

    walterw Gold Supporting Member

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    OK yeah, that would just attenuate a pinch of signal from the one coil.
     
  11. PawleeP

    PawleeP Member

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    may try this HB103N partially tapped (dial-able) with a 2000ohm pot until i can find a 10k or 25k linear
     
  12. PawleeP

    PawleeP Member

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    So, if it was a regular 3 lug 1 turn rotary pot, i suppose you would wire it (no-load)?
    thanx heretic, p
     
  13. bigtone23

    bigtone23 Member

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    If the trim pot is parked anyway, what if you measured the pot's resistance (at the sweet spot) and replaced it with a resistor of that value? That may be smaller and easier to tuck away in the cavity.
     
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  14. PawleeP

    PawleeP Member

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    have the neck (so far) tapped and ran to a switch, one side is open (for full bucker) then other pole is ran to mounted pot (25k for starters) so you can tap and run partial (to taste) on the fly.
    Am kinda confused about why people are recommending a 4.7k, 1.2k or 2.2k, then someone else recommending a 25k or 50K pot (non loaded)
    If not going with a hard wired resistor to ground (for the red/white tap) wouldn't a 2000ohm or 5k pot be closer to that of the recommended resistors? any help appreciated.

    Have the HB103 in neck already and am trying to decide on a HB103 or HB108 (have both) for the bridge. p
     
  15. fakeox

    fakeox Member

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  16. Terry McInturff

    Terry McInturff 40th Anniversary of guitar building! Gold Supporting Member

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    Is that the old trick of hooking a pot to the coil junction of a humbucker?
     
  17. fakeox

    fakeox Member

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    yes Sir, series to single.
     
  18. fakeox

    fakeox Member

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    So what do you think Terry(or anyone)?
     
  19. Terry McInturff

    Terry McInturff 40th Anniversary of guitar building! Gold Supporting Member

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    Back when I was playing with this idea I did indeed use an outboard/breadboard simple rig to sweep around to find that sweet spot. I seem to recall using a 1 meg trimpot (not at my notes right now). But whatever the pot value was, when I found the fave setting I measured the resistance and rigged a resistor(s) to an Allen Bradley "Mod Pot" (push/pull) to engage the resistor(s). Fortunately, with the advent of the CTS DPDT push/pull we finally again have a pro quality push/pull pot. For many years I was unable to offer such a pot, since the imports were (are) of such poor quality. I lost some biz due to not being willing to use those pots.

    Back to topic: it's a cool idea, but in my experience the true use of it only comes into play when using a humbucker with mis-matched coils, such as what me and Steve Blutcher at DiMarzio came up with in the '90's, which became the TCM Zodiac pickup that I used as standard for a bunch of guitars back then. One coil dominates the other and can truly stand on it's own as a single coil.

    I didn't ever really pursue the idea much (may be time to revisit it?) because under combat conditions (onstage) it never really found much utility for me. I have respect for those who enjoy the sound of a split PAF, whilst I have absolutely no musical use for it. But there are most likely other HB designs that would yield good enough fruit as to be good candidates!
    Here to learn!
     
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