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Control multiple A/R circuits with one potentiometer set

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  • Control multiple A/R circuits with one potentiometer set

    Dear everyone,

    This is my first post in the forum, so I hope I'm doing it right.

    I have managed to get an A/R (Attack / Release) circuit working (credit to synthnerd ) in which I input a square wave, can control the attack with one potentiometer and the release with another one and get the more or less expected shaped wave. This works fine:
    Click image for larger version

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    My question is: is there any way I can use the same 2 potentiometers to shape multiple waves? I could just replicate the same circuit for each wave, but I would like the same Attack values to apply all the waves as well as the Release ones. In that case, with one pot for Attack and one for Release I could shape 4 or 5 waves. Combining the waves into one is not an option as I later need to process them separately.

    Thank you very much in advance!

  • #2
    You could use Pulse Width control. Start with a triangle wave oscillator of 0-5V at maybe 10KHz, feeding 2 comparators the other inputs are from 0-5V pots. The comparator outputs control 2 analog switches.
    I can make a more detailed schematic if you want, but that is the general idea.

    Click image for larger version

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    • #3
      Wow, thank you very much for this great info. There are a few new concepts for me here and I've been researching a bit on them.

      I've been trying to follow the logic and there are obviously things I cannot yet see. Using a 5v single rail power supply I'll create a virtual ground and feed the comparators with +2.5v and -2.5:
      - comparator will output -2.5v for a certain period of time (depending on the pot shaft's position). Then it will output +2.5v. This would happen for both pots, sometimes they can overlap (+2.5v out from both comparators) and sometimes not.
      - switch will sometimes receive +2.5v (ON) and sometimes -2.5V (OFF) which will let the square signal flow or not.

      This logic takes me nowhere, so I'm sure I'm not understanding

      Could you explain a little bit further and / or show how & where 2 or more square input signals would be hooked and controlled only by 2 pots (Attack & Release)?
      Thanks a lot and apologies for my noobness, I'm very much learning.



      • #4
        The comparators have on one input a 10KHz triangle wave, on the other a voltage from the pot.
        The output of the comparators is a 10 KHz variable pulse width wave, the width dependent on the position of the pot.
        When controlling an analog switch it creates a virtual resistor.
        What is the voltage range you want at the A/R output?

        I've added limiting resistors, R1 would be 100 ohms and R2 is 1M. The short pulse on the left would create a high value resistor, the long
        pulse on the right a low value. A square wave would be half way between R1 and R2 or 500K.

        Click image for larger version

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        • #5
          Thanks for your answer once again,
          I am currently receiving 1V - 5V out from the A/R (depending on the position of the pots), so that would be more or less the expected value from each of the 4 waves.

          I'm still trying to follow your logic so I tried to put together a diagram to double check if I'm getting it (I apologize for this, I'm very amateur, self taught).
          Is the triangle wave combined with the pot, then sent to the 4 control pins of the 4066 to open and close and somehow work as resistances? So all the 4 switches within the 4066 would act as resistors (with the value specified by the pot)?
          I'll go and buy some 4066 and start putting it all together; I hope I can use TL072 op amps (as they are dual so I can use one chip for both A & R).
          Click image for larger version

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          • #6
            I am also self-taught starting at age 10, 54 years ago.
            Your diagram looks correct. Pin 7 of the 4066 would go to ground, pin 14 to +5v.

            The comparators in the first circuit would need to be 393 (dual) or 339 (quad) with pull-up resistors on the outputs.
            The triangle wave goes to the inputs of the comparators. When the wave goes above the pot voltage the output goes high (+5V),
            when it goes below the output goes to 0.

            Here is a easier way of generating a pulse wave using a 555 timer. Build two of these, one each for A and R

            Click image for larger version

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            • #7
              Thank you very much for your help, you definitely have a lot of experience in the field! I have started "learning" a bit more seriously only a few years ago (3 or 4 aprox.) and I'm 37...!

              I have tried the circuit with only one 555 (sending the square wave to both comparators) and it didn't work. Later I realized that you instructed to make two 555, so this is something that I still have to test. Unfortunately at the moment I am going thru hard personal issues and I'm being uncapable of working on it, but I will get back with an answer as soon as I can. Thanks again!



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