Liberation

Liberation is a ridiculous modulation machine. Based loosely on the Moog Liberation “ring mod” implementation of the 4046 CMOS PLL chip, but I couldn’t stop myself from turning the ugly up to 11.

Plug sound sources into In 1 and In 2, and you have a garden variety “ring” modulation effect: Input 1 + Input 2 + ??? = Magic. If I had stopped here, this would have been a handy little module. Yeah, and? Let’s kick it up a notch by mixing in the oscillator from the 4046, with CV over the rate, to add another layer of frequency modulation. Switchable timing caps allows for variety in the frequency range of the PLL oscillator.

We’re on a roll. No point stopping now.

Don’t have a second sound source? No worries, Liberation has you covered. Input 2 is normalled to a secondary internal oscillator. And not just any ol’ oscillator, but a stepped tone generator (aka Atari Punk Console). The STG has two CV inputs: one to modulate the reference voltage of the first oscillator stage on the 556 chip, with external CV input; one to modulate the frequency range of the second oscillator stage. There’s additional DC offset adjustment to the second CV, to shift a bipolar LFO up to unipolar, or just move the waveform around to achieve different modulation intensities.

Schematic

As with any schematic found on the internet, exercise caution when building. Test the build before plugging it into your case. If you find mistakes in the schematic, or you have recommendations for improving the design, feel free to contact me and let me know.

BOM

• Resistors
  • 100R (1) – R4
  • 1k (5) – R5, R8, R17, R19, R27
  • 6.2k (1) – R22
  • 10k (6) – R6, R7, R18, R24, R25, R26
  • 33k (1) – R10
  • 100k (12) – R1, R2, R3, R9, R11, R12, R13, R14, R15, R16, R20, R23
  • 300k (1) – R21
• Capacitors
  • 10nf (1) – C3
  • 100nf (3) – C1, C2, C4
  • 10uf electrolytic (1) – C5
• Transistors
  • 2N3904 (2) – Q1, Q2
• ICs
  • CD4046 (1) – U4
  • LM556 (1) – U1
  • TL072 (1) – U3
  • TL074 (1) – U2
• Potentiometers
  • 10k (2) – RV2, RV6
  • 100k (1) – RV1, RV5
  • 100k trim (1) – RV7
  • 500k (2) – RV3, RV4
• Switch SPDT (1) – SW1
• Audio Jacks (5) – J2, J3, J4, J5, J6
• Switched Audio Jack (1) – J1

Design Notes

The seed for this module was planted quite a while back, when I picked up an old PLL Synthesizer Cookbook at a second hand store. I was interested in the concept, but all the chips covered in the book have long been out of production. Fast forward to January 2026, when I stumbled on a YouTube demo for a Doepfer PLL module.

“Ooooo” says I, as the sounds poured forth from the little glowy box. “I want to go there.” A little poking around later, I discover that it is based on a 4046 chip. Hrm. Why does that sound familiar? Ah, yes, because I built one of these awesome modules by Barton Musical Circuits. And I happened to have some spares lying around to play with.

I’ll start by saying that there’s a lot going on in this circuit that you don’t need. If you want to simplify it, there are certainly features that could be cut, without losing any of the original modulation charm.

In the schematic, everything in the Stepped Tone Generator box can be ditched, if you don’t want to have an internal alternative to a second signal source. Replace Input 2 with a standard audio jack and disregard the APC label.

You could also get rid of the VCO range switch and use a single timing capacitor between pins 6 and 7 of the 4046 chip. Play around with it and find the range that works best for your needs.

For that matter, you don’t need to feed the VCO output on pin 4 back into the signal path. You could eliminate that mix pot and still have a very ugly modulation effect.

The output at pin 2 of the 4046 can go straight to an output jack, through a 1k resistor, if you’re not picky about your output waveform. Because the 4046 operates on a single, positive, power supply, it outputs a unipolar waveform, that is around 12v peak-to-peak.

I’m running this through an inverting op amp to tame the amplitude, then through another op amp where the noninverting input is connected to the positive and negative power supplies, through a 100k trim pot. This trim pot is used to introduce a DC offset to shift the output down to a bipolar signal that’s roughly 10v peak-to-peak, centered on 0v. If you don’t mind having a hot, unipolar waveform at the output, feel free to skip those last two op amps.

Likewise, if your input signals are unipolar, you can probably get away with skipping the NPN transistors in the input stages. These convert a bipolar waveform into a unipolar signal that the 4046 can work with. If all of your signal path is unipolar, you likely don’t need these.

Demo

Coming soonish