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Thread: what resistors to make a 500K pot into a 100k? please

  1. #1
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    what resistors to make a 500K pot into a 100k? please

    Hiza, I picked up a Armstrong Rock Treble pickup and it needs to see a 100K volume & 200K tone. Would anyone be so kind as to tell me what resistors i need for each so i can use a couple of my handful of 500k sitting in my parts box? Oh and to what lugs would they go?

    Cheers, J

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    Senior Member Enzo's Avatar
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    If I had a 500k pot and wanted to make it 100k, and I was not up to doing the math, I would do it empirically. I would take another of my 500k, and with a couple clip wires to one end and the wiper, connect it in parallel the original 500k. I'd connect my ohm meter probes across the original pot too. Now I dial the new pot down until my ohm meter says 100k. Now don't move anything, but unclip the wires, and measure the resistance set on the new pot. That would be the resistance you;d need. Chose a resistor of the nearest standard value to that.
    Education is what you're left with after you have forgotten what you have learned.

  3. #3
    Supporting Member Jazz P Bass's Avatar
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    Just a thought, but paralleling a resistor, usually messes with the taper.

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    I don't own an ohm meter...

    I'm ok with it messing up the taper as long as it basically works...

    anyone?

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    Supporting Member The Dude's Avatar
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    125K for the volume and 333K for the tone. Whatever standard values you have close should be fine. This is simply an answer to your specific question. I'm not making any judgement as to whether it's necessary or a good idea.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

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    Senior Member Enzo's Avatar
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    Specifically then 120k and 330k are common standard values close to those. That assumes also that your 500k pots actually measure 500k resistance. Pots notoriously have poor tolerance - in my experience.
    Education is what you're left with after you have forgotten what you have learned.

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    Supporting Member The Dude's Avatar
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    I'll add: If you're trying to copy the old Dan Armstrong electronics, I believe you have it backwards. The Volume should be 200K and the Tone should be 100K, but then I'm not 100% sure what you're up to. As an example, see the first diagram here:

    Dan Armstrong Registry FAQ - DA Registry
    “Yeah, well, you know, that’s just, like, your opinion, man.”

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    Whoa... thanks. I knew it was something like that! So does that mean i add 125K resister for the volume and 333K resister for the tone to get them each close to 100 and 200k? Or, are you saying there are readily available pots of 120k and 330k... ?

    sorry, i just play the damn things!

  9. #9
    Supporting Member The Dude's Avatar
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    125K (or standard value of 120K) with the 500K will get you close to 100K.
    333K (or 330K standard value) with the 500K will get you close to 200K.
    There are 100K and 200K pots readily available if you wish to forget about paralleling resistors.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  10. #10
    Supporting Member Jazz P Bass's Avatar
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    I agree.
    The chances of having oddball resistors to get the final results are probably slim. (unless we are dealing with a well equipped shop)
    Just buy the correct pots.

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    As Enzo points out, pots have a slack tolerance and I doubt that the difference between a 333k and 330k resistor would be audible. I have some 250k guitar pots that read 218k, and some 500k that read 570k.

    A Suhr guitar I recently worked on use a Superswitch to reduce the 500k pots to 250k when switching from humbucker to single coil. They just parallel a resistor across the outer lugs of the pot to reduce the value and it works just fine.

  12. #12
    Senior Member Enzo's Avatar
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    And for that matter, 333 is less than 1% off 330, so a common 5% 330k might well measure 333k anyway.
    Education is what you're left with after you have forgotten what you have learned.

  13. #13
    rjb
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    Quote Originally Posted by Jazz P Bass View Post
    Just buy the correct pots.
    That.

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    Thanks much!!

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