Yet another Strat treble bi-pass thread

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by KeithC, Aug 13, 2006.

  1. KeithC

    KeithC Silver Supporting Member

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    My dilemma has been with the Acme type treble bleed mod,which is a 680pf cap in parallel with a 220k resistor, that it actually is brighter when when the guitar volume is rolled down.
    It gives the impression that it is actually cutting the highs at 10 but I assume it is just actually letting more highs pass through at around 5-8.
    I tried taking out the resistor and using just the 680pf cap alone and it does help some but it still a little muddier on 10.

    Do I need a slightly smaller value cap alone or a slightly higher value cap?
    Trying to get it even all the way up to 10

    Thanks
     
  2. Clorenzo

    Clorenzo Member

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    Two options:

    - A smaller resistor. The only problem with this is that it will "linearize" a bit the taper of the pot, but you may be ok with that. I'd wire a 250k pot as the resistor, adjust to taste, measure value in preferred position, replace with corresponding fixed resistor.

    - A smaller cap. This will reduce the effect without changing the taper but at the same time will increase the frequency of the resonant peak, changing the "voice" of the pick up somewhat as you turn the volume down. Try the standard 470 / 330 / 220 pF values, or better still, buy a bunch of 100 pF caps and put as many in parallel as required.
     
  3. KeithC

    KeithC Silver Supporting Member

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    Thanks for that info.
    So you are saying to run some leads off the volume pot and connect them to a 250k pot and see where it sounds the best?
    Would I connect the wiper to wiper and hot to hot?
    Also, how would I measure the resistance at that point?
    I know with my DVM but where do I connect up?

    Thanks
     
  4. Clorenzo

    Clorenzo Member

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    Yes, just use the extra pot as your bypass resistor (together with the cap of course), wiper to wiper and hot to hot. Try it at different possitions till you like what you hear, then remove it from the circuit (careful not to change its position), measure between its wiper and hot and get a fixed R of the closest standard value.
     
  5. KeithC

    KeithC Silver Supporting Member

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    That clears it up perfectly.
    I'll give that a try!

    Thanks :AOK
     
  6. suhr_rodney

    suhr_rodney Supporting Member

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    My money is on a 150k ohm resistor... of course, resistors are cheap! :D
     
  7. justicetones

    justicetones Member

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    Yup. I use 150K resistors and a 680pf cap. I have tried many and recently tried this and I like this the combo best. KeithC email me your address and I will mail you a set of the combo I use. They are very high quality components.
     
  8. suhr_rodney

    suhr_rodney Supporting Member

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    Justicetones, what components do you use and where do you get them?
     
  9. justicetones

    justicetones Member

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    I get them from DigiKey.com.
    For the Resistors

    150KXBK-ND RES 150K OHM 1/4W 1% METAL
    FILM $ 0.10

    -----OR-----

    P150KBBCT-ND RES 150K OHM CARBON FILM 1/2W 5% $ 0.10

    and for the capacitor

    399-1826-1-
    ND CAP 680PF 50V 5% CER AXIAL $ 0.29

    These are the part numbers, specs and cost rounded up to the nearest penny.
     
  10. KeithC

    KeithC Silver Supporting Member

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    Thanks. Email sent. But I'll cough up for the parts and shipping!
    :AOK
     

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