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Log or Linear volume pot in your amp?

Discussion in 'Shock Brother's DIY Amps' started by Uncle Daddy, Apr 17, 2021.

  1. Uncle Daddy

    Uncle Daddy Tele-Afflicted

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    My Fender style amps both have a1M volume pots, but the Princeton Reverb is a bit more manageable at low volume, whereas the Brown Deluxe goes from 0-60 in a heartbeat. Is there a log pot with more of a scoop on the curve?

     
  2. Uncle Daddy

    Uncle Daddy Tele-Afflicted

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    Would adding a resistor between the ground tab and the wiper scoop the curve more?
     
  3. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    The best article I know on taper resistors (and pots in general) is by R.G. Keen. *But* his discussion is about adding resistors to get a log-like taper out of a linear pot.

    http://www.geofex.com/article_folders/potsecrets/potscret.htm

    Smart folks may well know how much resistor to add to a 1ML to lessen the initial slope.
     
  4. dan40

    dan40 Friend of Leo's

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    The 6g3 makes quite a bit more gain in the first stage and has a tonestack that keeps much more of the signal voltage than the one used in the PR. This may have something to do with the very fast volume transition. I have found that using a PEC 1m pot helped to even out the taper a bit better than some of the other brands.

    https://www.tubesandmore.com/products/potentiometer-precision-electronics-audio-slotted-shaft

    I recently noticed a new brand of pot at Antique Electronics that looks promising at a much lower cost. I purchased a few but haven't had the chance to test them out yet.

    https://www.tubesandmore.com/products/potentiometer-tocos-rv24-audio-10-6mm-shaft
     
    King Fan likes this.
  5. printer2

    printer2 Poster Extraordinaire

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    This increases your loading of the previous circuit. And yes, different manufacturers can have different log slopes. More than not you will find the pot only has two slopes to the response to approximate the log response. A shallow slope then a greater slope.
     
  6. radiocaster

    radiocaster Poster Extraordinaire

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    Does Fender really not use logarithmic pots for the volume? The schematics seem to say otherwise, unless I'm missing something.
     
  7. Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    Maybe try replacing V1 in the 6G3 with a 5751.
     
  8. Mexitele Blues

    Mexitele Blues Tele-Afflicted

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    Older Fender amps use J-taper pots instead of log.
     
  9. Uncle Daddy

    Uncle Daddy Tele-Afflicted

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    Funnily enough, I was reading about those earlier. A reverse hump rather than a ski jump curve to ramp up the volume faster.
     
  10. printer2

    printer2 Poster Extraordinaire

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    Looking though some of my threads I found a graph I was thinking about. I took the resistance readings of a pot using a Fender 1010 knob as the way points. The bottom of the graph is the knob positions. The left axis is the resistance. The lower plot is the 'Log' pot. It was a dual pot so that is why the two lines. Not that far out from each other, makes for a good stereo experience. It is easier and cheaper for the manufacturer to have two resistance slopes to approximate a log slope. Not like too many people complain, 3.5 is not loud enough for you, you turn it up to 4.

    [​IMG]

    I had a 10V source feeding the pot. I hooked up two pots the way a 5E3 is arranged and used a 51k resistor to simulate the impedance of the tube plate feeding the pots. The top line is the voltage out of the instrument channel pot with the instrument channel at 10 and stepping the normal channel through its rotation. Full output till you get to 6 and then slopes down to half voltage when you get to 10 because of the other channel loading it down. The blue line in the lower middle is the normal channel on 10 and stepping the instrument channel from 0 to 10. The line above it is the normal channel at 0 and the instrument channel from 0 to 10. It probably would have been good for me to plot the curves with a log scale on the left side to give a response that our ears would hear from the rotations, it was a quickie experiment. I would like to do it with the actual preamp circuit one day and also map out where the amp starts distorting. So many ideas, so little time.
     
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