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JMP-1 encoder mod

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  • JMP-1 encoder mod

    Ive read in other forums about fixing the data wheel issue in the JMP-1 Marshall preamp. I just got one and the patches jump around when turning the control. I guess this is common in these units . They are adding a de-bouncing chip. No one mentions "how"

    here : https://www.mouser.com/ProductDetail/863-MC14490DWG

    https://www.mouser.com/ProductDetail...CW1J-C36-CC24L


    so the encoder is 3 pins and the chip is 16 pins.

    Has anyone done this mod? Is there a scem , or can someone tell me how to do this ??

  • #2
    When the encoder ages it tends to be unstable, making the adjustment difficult.
    When it is new, its precision is total.
    Sometimes I have cleaned them and they work better, but if the degradation due to use is excessive, it is enough to order a new one.

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    • #3
      "The circuit I used was just the standard circuit in the MC 14490 data sheet, and I attached the PCB to the back of the encoder with foam tape."

      http://www.marshallforum.com/threads.../#post-1167049
      Originally posted by Enzo
      I have a sign in my shop that says, "Never think up reasons not to check something."


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      • #4
        i found some help--thanks though

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        • #5
          Debounce? It didn't need debouncing when the parts were new. Seems like a lot of extra effort to get around replacing a worn control.
          Education is what you're left with after you have forgotten what you have learned.

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          • #6
            Apparently the datasheet for the encoder shows a recommended debounce circuit. Not sure if that means it is recommended to use one, or if it means if you are using one, here is the recommended version.
            Originally posted by Enzo
            I have a sign in my shop that says, "Never think up reasons not to check something."


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