Input volume pot swap question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by dewman, Dec 7, 2014.

  1. dewman

    dewman Gold Supporting Member

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    Nov 23, 2005
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    NC
    I had to replace a 500k alpha linear pot recently on an amp just before a gig, and only had a 1M log PEC pot lying around. the amp seems to be considerably louder but isn't exactly the same tone, seems more of everything...volume isnt the only thing, the transition to overdrive is definitely quicker and the amp seems to have less headroom before getting all farty. I know the tapers are different, but it just seems like the amp has more of everything.

    Was this to be expected? I tried to google relationships between volume pots and amp tone and gain structure but nothing helpful. I'm well aware of pot values and tone in guitars, but not in amps...Any tech heads care to chime in?
     
  2. pdf64

    pdf64 Member

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    The headroom (ie in terms of the capability to put out the same clean and overdriven SPL) should be pretty much identical, however, depending on the taper, the control resolution to achieve that may be more awkward.
    The stage that feeds the control will likely have a fraction more gain and voltage swing into 1M than 500k, but it's unlikely to be significant.
    Unfortunately many guitarists seem to confuse 'higher gain' with 'decreased headroom (and visa versa), so all bets are off for how you may perceive this
    If your amp performs the same as before when the amp volume is set to max, then any differences between old and new pots are most likely due to the taper.
    Alpha USA audio taper standard tends to be 15%, depending on where you buy them from
    http://www.alphapotentiometers.net/html/taper_curves.html
    http://www.alphapotentiometers.net/html/24mm_pot_12.html
    For PEC, you'll have to check with your supplier, eg http://www.precisionelectronics.com/0-40a-010c.html
     
    Last edited: Dec 7, 2014
  3. Diablo1

    Diablo1 Member

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    You could solder in a 1M resistor across the pot to create a 500K pot. The taper will be different than original, but you can see if you like it better for the original tone.
     
  4. dewman

    dewman Gold Supporting Member

    Messages:
    5,751
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    Nov 23, 2005
    Location:
    NC
    Yeah thanks. That should get me through for long enough to order a replacement pot
     

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