Hot!using digital pot rather than analog pot

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brownt
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2018/06/14 00:28:15 (permalink)
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using digital pot rather than analog pot

Hi,

I would like to use a digital pot in place of the analog pot in this circuit. However, it does not work properly. There are some very tiny sound fluctuations but that is all. I wonder what needs to be done, or why its not working as expected, or how I can work out what the problem is.

thanks

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#1

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    DarioG
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    Re: using digital pot rather than analog pot 2018/06/14 01:38:46 (permalink)
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    Hmmm should work, more or less...

    GENOVA :D :D ! GODO
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    brownt
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    Re: using digital pot rather than analog pot 2018/06/14 01:55:13 (permalink)
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    hmmm, yes less in this case. The fluctuations are what one would expect from a wah wah circuit (bandwidth filter changes), but the freq range change is very small and short, more like a "thip thip" than a "waaaaah waaaaaah".
     
    perhaps something to do with the power supply for the digital pot???
    #3
    DarioG
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    Re: using digital pot rather than analog pot 2018/06/14 02:02:20 (permalink)
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    Yep I know a wah-wah more or less :) even if I never built one.
     
    I considered that thing about power at pot legs getting past what it accepts but... since there are capacitors in place then it should not happen.

    GENOVA :D :D ! GODO
    #4
    qɥb
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    Re: using digital pot rather than analog pot 2018/06/14 02:07:22 (permalink)
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    How is the pot powered?
    The signal must NOT go outside the power supply levels, so your power supply must share a ground reference with the signal.

    This forum is mis-configured so it only works correctly if you access it via https protocol.
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    #5
    brownt
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    Re: using digital pot rather than analog pot 2018/06/14 04:06:55 (permalink)
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    The power supply is 0 - 5 volts, and the signal, because of the caps, is AC and so sometimes below 0 volts. So, do i need a positive & negative supply so the signal does not go outside the power supply levels?
    #6
    DarioG
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    Re: using digital pot rather than analog pot 2018/06/14 04:16:17 (permalink)
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    Ah well yes, in this case I think you should bias the "signal" sides with some 2.5V

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    brownt
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    Re: using digital pot rather than analog pot 2018/06/14 04:22:18 (permalink)
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    So, I need a couple of equal value resistors from VDD and VSS to the signal line.
    Is that on the pot side of the caps, or the other side.
    #8
    DarioG
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    Re: using digital pot rather than analog pot 2018/06/14 04:35:43 (permalink)
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    all, that is floating - so I'd say the other except (obviously) ground

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    rpg7
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    Re: using digital pot rather than analog pot 2018/06/14 04:54:46 (permalink)
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    Also if the pot is going to change rapidly on could experience the "zipper" effect.
    https://www.sweetwater.com/insync/zipper-noise/
    #10
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