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4046 PLL Frequency Multiplier Module

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  • 4046 PLL Frequency Multiplier Module

    I found an intriguing sketch for a "PAiA Fatman Frequency Multiplier Module" (see link) and thought I could put my 74HC4046A chip and all the flip flops I have laying around to good use by recreating it. Unfortunately, the sketch has me stumped right from the beginning: why is Vcc going to ground and the GND input of the chip to -12V? I understand that it will still work in principle since all voltages are being shifted down by 12V, just not why. Why not connect the usual way with Vcc at 12V and GND to 0V?

    I should add I'm a novice with no experience with Fatman systems.

  • #2
    That is odd. Maybe PAIA powered their modules from -12, and that's the way they use to get positive-power components to work with a negative rail. Any PAIA hobby builders here? They had a lot of kits available in the 1970's.
    This isn't the future I signed up for.


    • #3
      My best guess is the designer wanted to share the load between the + and - power supplies.
      More important though is that the 74HC4046 maximum power supply is 7V. You need to use the MC4046 or CD4046


      • #4
        Ah thanks to you both (including the maximum power hint). I never would have thought about sharing the load as a possibility .


        • #5
          One problem with this circuit is that the input at pin 14 will have to be 0 to -12V. It would be better to run the chips on +5v, then you can use the 74HC series and the input would be 0 to +5v like most other logic.
          Instead of the 324 op-amp at the output you would need one that works on 5V like TLC271


          • #6

            9308 FatMan MIDI Channel Select DIP Switch
            It's All Over Now