Volume pot taper

Discussion in 'Tele-Technical' started by LKB3rd, Aug 13, 2013.

  1. LKB3rd

    LKB3rd Friend of Leo's

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    I just noticed a Tele has an uneven taper to the volume knob. All of its useful range is from say 5-10 on the dial. Would this be related to the pot, or something like a capacitor?
     
  2. KokoTele

    KokoTele Doctor of Teleocity Vendor Member

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    That's all about the pot taper. You can modify the taper of the pots by putting a resistor across the input and output lugs. This will make the taper more linear, giving you more useable range in the bottom and middle, though the apparent volume increase in the high end of the range is flatter.
     
  3. jamesgmac

    jamesgmac TDPRI Member

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    KokoTele, I'd like to try adding the resistor. How do I know which are the input and output lugs? Any suggestion for resistor value?
    Thanks!
    Jim
     
  4. LKB3rd

    LKB3rd Friend of Leo's

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    So if I got a regular CTS 250k audio taper volume pot and swapped it in this should fix it? If it's an out of spec pot I think I'd rather just swap it out than use a resistor.

    ETA: I just found this via googling
    http://www.thegearpage.net/board/archive/index.php/t-850628.html


    So I'd imagine something like a 200Kohm resistor on a 250k Tele pot would get a similar result... I am warming up to this idea now :)
     
  5. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

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    I believe a linear pot will give you more volume at a lower setting, i.e. the loud covers more of the rotation. An audio pot will allow volume swells, IME
     
  6. LKB3rd

    LKB3rd Friend of Leo's

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    Yes, my googling reveals I probably have an audio taper pot which is too "audio" for my preferences. Taming it with a resistor seems like a good plan if I could verify what value might work to make it less abrupt.
     
  7. KokoTele

    KokoTele Doctor of Teleocity Vendor Member

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    This is just silly. No matter what style the pot is, it has a position that equals a certain resistance. If the guy likes the clean sound he gets when his 250k audio pot is dialed down to, say, 150k, he will get the identical tone as when he dials a 250k linear pot down to 150k.


    The problem with the modern audio taper pot is that they have almost all of their useable range in the last 1/4 of the turn. The problem with a linear pot is that they have almost all of their useable range in the first 3/4 of the turn. Some of the custom taper pots are a little better.

    Try a 250k resistor and see how you like it. The value isn't as critical as you'd think. Try out some others to prove it to yourself. The easiest thing to do is to get some alligator clip leads and clip it in temporarily.

    There are 3 lugs on the pot. One of them is grounded. The middle one is the output, the remaining one is the input.
     
  8. LKB3rd

    LKB3rd Friend of Leo's

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    Thanks Kokotelepeli :D
     
  9. jamesgmac

    jamesgmac TDPRI Member

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    thanks koko, i can't wait to try that tonight. it's the one thing about my tele that i've never liked. sounds like it'll do the trick just fine!
     
  10. jefrs

    jefrs Doctor of Teleocity

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    A linear (lin) pot does what is says on the tin. It is smooth and linear, not a lot happens until you drop to 5, it's more of a fine adjustment knob. I prefer linear, most don't.

    A logarithmic (log) pot tries to emulate a logarithmic curve. They are made by laying four linear tracks end to end. The result is it has steps, sometimes we notice them.
    A mini pot tends to have a more noticeable step than a full-size. Alpha and CTS full size are the same quality but slightly different taper, and different shaft size.

    Putting a resistor of about 0.8 the value of a linear pot between top and wiper makes a very effective and smooth pseudo-log pot.
     
  11. jamesgmac

    jamesgmac TDPRI Member

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    Thanks KokoTele! I just added a 100k (all I had) resistor. The difference is night and day. Before the usable volume was from about 7 or 8 to 10. Now it's from 2 to 10. Just awesome now.
    Thanks again!
    Jim
     
  12. jefrs

    jefrs Doctor of Teleocity

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    Putting a resistor across the top input and the wiper output can drop the load on the pickup when you roll off the vol pot, and turn it into a bit of a tone control.

    A linear vol pot does become nicely logarithmic but also variable load.
    Do try it with the stock log pot by all means, but putting a resistor of 0.8 x the value of the pot was intended for linear pots because the normal log pot is not logarithmic enough for some purposes. The value of "0.8" comes from Morgan Jones "Valve Amplifiers".
    Putting the resistor across bottom ground and wiper output will make a reversed log pot (left-handed not antilogarithmic). Using one on a log pot will probably smooth over the hump between its linear tracks.

    Because the resistor drops the load, to see what work best, you might try (E12 series)
    250k Lin + 180k or 220k (0.8=200k)
    300k Lin + 220k or 270k (0.8=240k)
    500k Lin + 390k (0.8=400k)
     
  13. printer2

    printer2 Poster Extraordinaire

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    Cheaper to make Log pots with two elements. Measured this for a discussion on 5E3 volume controls (being lots of control around 0-3 and then not much change), the relevant curve is the bottom one. It is labeled voltage but I just used voltage to measure the resistance (if you don't understand that just ignore it).

    The bottom plot gives percent output to pot rotation on the bottom. As good a log curve you can get with two straight lines (two different resistive elements in a pot).

    [​IMG]
     
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