what does this resistor do in this diagram

Discussion in 'Just Pickups' started by hopdybob, May 21, 2019.

  1. Dennyf

    Dennyf Tele-Afflicted

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    To be fair, since they chose a 300-ohm pot when they clearly had 250s available, my guess would be that it changes the taper in some desirable way.

    FWIW, audio taper is actually a kind of "tempered" log taper. I personally prefer true log taper ("D" taper) pots on my guitar, especially if I'm in a "gainy" mood.
     
  2. simoncroft

    simoncroft TDPRI Member

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    I know this probably isn't the answer you seek @hopdybob, but if you connect the resistor to a couple of wires long enough to go past the edge of the pickguard/scratch plate and add a small toggle switch, you'll be able to put the guitar back together for test purposes. Then you can find out whether the resistor makes any difference to you, and if you prefer the circuit with or without.

    To me, that would be more important than the theoretical issue of what the resistor is supposed to be doing in the circuit. Then again, I have no idea what the answer to that is! :twisted:
     
  3. Asmith

    Asmith Friend of Leo's

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    I'm not disputing that the changing the load value by 10% wont make a difference, it's just that unless they're sorting through the pots going into these guitars to ensure they get 300k pots with a 5% or less tolerance (then throwing the rest) that 10% or 25k ohms is out of thier control. The load can still be anywhere 220k and 325k, they may as well buy 250k pots or 300k pots and just sort through those to find the ones with a 275k value out of the pick. It's a marketing gimick so they can say they spent time modifying the electronics.

    If I was serious about a consistant load value I would put in a multiturn 5Meg Trimmer inside the guitar and twiddle with that till the pot value and the trimmer make the ideal value.
     
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  4. mitchfinck

    mitchfinck Tele-Holic

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    Change the taper and frequency response a little bit.
     
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  5. Antigua Tele

    Antigua Tele Friend of Leo's

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    John probably said to Paul "can you make it 5% brighter?" and Paul said "anything for you, John!" , and there's your resistor.
     
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  6. Teleterr

    Teleterr Friend of Leo's

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    1 Sure the pot values might be off, so the same % of the ( pots + resistor ) circuit values will be at or near the target 275 K or whatever, value as Fender's standard circuit.
    2 The taper will be different. I ve never noticed that it made a difference the times I ve added the resistor, but then again I'm fine w linear or audio , theres a difference, but I don t care.

    Maybe John liked both the new loading and taper after the new resistor was added. So instead of explaining that it might or might not be important due to tolerences of pots being crappy, they just added it to placate him.

    In summary pot/resistor value chosen to be a value different from standard pots. It can vary , but thats always the case w 250-500 pots as well. New contour that may be desired or coincedental. No way to know w-out asking.
     
  7. Antigua Tele

    Antigua Tele Friend of Leo's

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    Don't make too much of the pot taper, because in the same respect that pots have imperfect resistances, they have imperfect tapers as well.

    [​IMG]

    Most log pots are segmented into linear sections that loosely trace the ideal curve, and those segments are not consistent from one pot to the next. In the manufacturing process, the carbon strip of log pot is applied in segments, and so these linear runs correspond to those difference segments.

    Here's a video where someone plots at the actual curve of a cheap log pot



    Also this is a really good read http://www.geofex.com/article_folders/potsecrets/potscret.htm
     
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  8. Rob DiStefano

    Rob DiStefano Poster Extraordinaire Vendor Member

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    forget the silly vol pot added resistor - look at the .1uf tone pot cap. mud city sweep, and if that tone pot isn't a no-load the overall tone will be affected.
     
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  9. garrett

    garrett Tele-Afflicted

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    Agree with all that it's negligible.

    My fave tweak is that they leave the control cavities unpainted to allow the wood to breathe. o_O:lol:

    They sound darn good, though.
     
  10. JuneauMike

    JuneauMike Friend of Leo's

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    Yeah, I'd say its a volume contour resistor. At that value it would keep some highs from bleeding off. I don't think it affects the value of the pot. Kind of a sparkle mod, I guess.
     
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  11. Antigua Tele

    Antigua Tele Friend of Leo's

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    Seeing as how the pot is 300k, it would have more sparkle without the resistor.
     
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  12. JuneauMike

    JuneauMike Friend of Leo's

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    Hmm, I went the wrong way. Then it would make a 300k pot a 272k pot. That would make a 250k pot slightly more sparkly. Maybe 300k was too much with those pickups.
     
    Last edited: May 21, 2019
  13. Antigua Tele

    Antigua Tele Friend of Leo's

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    According to this LTSpice model, using values from the diagram along with reasonable approximations, the resistor would not make an audible difference. The change in the resonant amplitude is only about 0.2dB.

    [​IMG]
     
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  14. JuneauMike

    JuneauMike Friend of Leo's

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    Why would amplitude be the measured variable? Just curious.
     
  15. hopdybob

    hopdybob Tele-Holic

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    Rob, do you mean that you will get a very dark sound, darker than the sound off Mayer sound in hiss own version off crossroads?
     
  16. hopdybob

    hopdybob Tele-Holic

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    i thought about that to trying it out, but its with a strat clone so a little more trouble than with a tele.
    but maybe i will try that
     
  17. Antigua Tele

    Antigua Tele Friend of Leo's

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    The pickup puts out a voltage, so it all comes down to amplitude by frequency.
     
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  18. teleaddicted

    teleaddicted Tele-Holic Gold Supporter

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    That big resistor is basically wired in parallel with the whole pickup circuit, going from the switch output to ground.
    For testing purpose you could just apply the resistor on the output cable jack lugs not needing to open the controls plate/pickguard.
    It's effect should be like using a TBX passive tone pot dialed on "10" although I find 3M ohms to be a little overkill (the TBX dialed on 10 is basically only a 1M ohm wired in parallel with the whole circuit).
    The effect will be subtle, but it's there and will be more effective with low wind low capacitance/inductance single coils than humbuckers: it should clean up some of the bass and slightly enhance treble.
    I permanently applied a 1M ohm resistor on the output jack lugs of my Bullet Strat (cheap ceramic pickups) and a 2M ohm resistor in my hombrew Affinity Cabronita (overwound japanese old Filtertrons) with good results.
    The effect is there also taking the vol/tone pots totally out of the equation, that is going straight from the switch to the output jack.
    I can't figure out the math of it, but it works and it saves buying a TBX to put in a cheap guitar if all I want is that resistor.
    Just my couple of scents...

    .
     
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  19. Rob DiStefano

    Rob DiStefano Poster Extraordinaire Vendor Member

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    NO. mayer is fuzzed out and flesh picking, which will mask the inherent treble of the guitar. a .1uf cap kills treble Fast, little to no sweep of shunting treble to ground. a .022uf to .015uf cap allows for a usable range of treble killing and stops the tone pot from becoming a treble on/off switch. better yet, make the tone pot into a no-load.
     
  20. Chunkocaster

    Chunkocaster Poster Extraordinaire

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    It's just some minor protection added against lightening strike.
    I recently rewired one of my tele's and clipped some resistors off the volume pot because I like to live dangerously.
     
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