Bad 4046 Audio Circuit

A project log for Zappotron Super-Sequencer

NES Zapper Controlled drum sequencer

Russell KramerRussell Kramer 03/22/2017 at 03:280 Comments

Now that the control voltages are working I need something to control. A vary popular chip for electronic music hobyists is the CD4046 voltage controlled phase locked loop oscillator. It generates a 50% duty cycle square wave controlled by the VCO input voltage and with max and min frequencies set by two resistors and a capacitor.

I hooked up the standard circuit and it worked; but I didn't like the sound. It was too simple and clean. It was the kind of simple beeps I'd expect from a microwave or a printer that wants more paper. Purely by accident I discovered that disconnecting the Vcc pin from 5v produced a much more interesting dirty sound. I'd have never thought to try that deliberately. Shouldn't the chip just be off if it's not getting any power? I'm assuming it's drawing power from the VCO control input because there isn't anywhere else it could come from.