This is the Dual VCO PCB, a dual-frequency playground based on the classic CD4046 Phase-Locked Loop (PLL) chip. Each IC acts as a Voltage-Controlled Oscillator, producing a frequency that changes with input voltage — perfect for driving tones, modulating patterns, or creating pitch-reactive effects.

Most VCO circuits use one chip and a few fixed inputs. I went the other way: this board includes two independent CD4046s, each with 10 input points that you can patch any way you want — ideal for pairing with the Decade Sequencer, Hex Oscillator, or Quad Modulator. All 10 points eventually feed the same pin on each IC, meaning you can combine triggers, mix voltages, or send chaotic logic signals into a single control input.

The result? Unpredictable, musical, and totally alive.

How it came to life

When I first revisited the CD4046, I noticed how rarely people explored its full potential. So I decided to double it up — two VCOs side by side, each free to react to whatever voltage chaos you throw at it. It’s a circuit that doesn’t tell you what to do — it invites you to experiment.

You can treat it as a pitch generator, a voltage-to-frequency converter, or even as a modulation engine for your existing logic synth modules. The Dual VCO loves being clocked, fed, and confused.

What makes it special

• Two independent CD4046 VCOs — dual sound sources in one board.

• 10 patchable inputs per VCO — ideal for pairing with the Decade Sequencer.

• Voltage-controlled madness — feed it any control voltage, pulse, or logic pattern.

• Cross-modulate or sync both oscillators for rich evolving tones.

• Maker-friendly layout — large pads, clean silkscreen, forgiving spacing.

• Runs on 9 V DC — standard modular or battery power.

• Educational & hackable — explore how voltage turns into frequency.

What you get

• 1 × Dual VCO PCB (silkscreen + drilled).

• PDF including schematic and BOM.

Who it’s for

• DIY synth builders, educators, and experimenters.

• Makers exploring voltage control and sound synthesis.

• Anyone who wants to turn logic pulses into evolving tones.

Collect all 6 modules to create your own Audio Sequencer with modulation!