The part of the circuit I'm having trouble implementing is the transistor pair that are used to control the output frequency (going into pin 11 of the 4046).Thomas Henry X-4046 Schematic

I have removed the Exp FM, Linear FM, hard sync, 1V/Oct and sine and pulse outputs as I am just interested in creating a triangle, rampoid or sawtooth output with an adjustable frequency. My circuit currently looks like so:

My 4046 Multisim Circuit

However, I am confused about where the output of Q2 should actually be connected. According to the schematic, it should be connected to pin 11, however, the CD4046B data sheet shows that pin 11 is connected to the VCO:

CD4046B schematic

I've tried connecting it to both the LPF output and the VCO output (which is fed back into the phase detector input), but neither of these seem to have any effect on frequency.

I'm not sure if there are other problems with my circuit too, although I've followed the schematic pretty much exactly. If there are I would appreciate them being pointed out, as this is my first time building a synth.

edit: the circuit for the outputs of pins 4, 6 and 7 can be found here: http://www.birthofasynth.com/Thomas_Henry/Pages/X-4046.html#X-4046_VCO_Schematics


1 Answer 1


That 4046 has nothing to do with Thomas H., he just used that chip in his circuit. No need calling it "Thomas Henry X-4046" just "4046 PLL" is sufficient.

Have a look at this datasheet page 11:

enter image description here

There you see that pin 11 is connected to the source of an NMOS. That circuit converts the input voltage from pin 9 (the VCO input) into a current which flows to P1.

So pin 11 is a current input, it wants you to sink a current from it to ground. That's what Q2 does in Thomas H.'s circuit.

Your PLL model very likely only accepts a voltage as input.

The circuit around Q1 and Q2 is for frequency modulation, you can achieve the same by just adding a voltage to the voltage you already apply to the PLL model's input.

How to exactly implement that depends on your circuit and goes too far to describe here.

  • 1
    \$\begingroup\$ I understand that it has nothing to do with him, but it's his circuit that I'm trying to implement in Multisim. \$\endgroup\$
    – Tom_Anks
    Nov 1, 2017 at 10:05
  • \$\begingroup\$ So I could use a summing op-amp to sum the voltage outputted by the transistors and the initial input and connect the output of this op-amp to the PLL input? \$\endgroup\$
    – Tom_Anks
    Nov 1, 2017 at 10:06
  • \$\begingroup\$ Yes that could work. \$\endgroup\$ Nov 1, 2017 at 10:12

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