do negative voltages really destroy cmos?

synthesist

I build the adsr-generator circuit from nicolas and it's supposed to spit out about -3 to +3 volts.
I also build a VCO out of the cd4046 cmos chip, it is powered by +9 volts and ground. It has an CV input where I fed the signal of the adsr circuit. Everything seems to work fine though.
But it shouldnt, or? everytime the signal reaches down to the negative voltage it is like the cmos chip gets poled the wrong way.
Or can I assume that it will break after some time?

Clack · Posted: Mon Sep 26, 2011 12:10 am Post subject:

it probably isn't going low enough to pull the input of your VCO negative (but then I hav'nt seen your vco's layout so who knows)

A diode pointing from GND to your input should protect it

synthesist · Posted: Mon Sep 26, 2011 3:30 am Post subject:

thanks for your answer.

Yesterday I connected the adsr- signal to the anode of a diode, the cathode is pointing to the CV input pin of the vco circuit. Works fine so far.
Is this also a way to secure it from the neg. voltage?

Clack · Posted: Mon Sep 26, 2011 10:55 am Post subject:

yes that will also work , although you will experience a voltage drop of around .6 which wont really be noticeable with an envelope generator > VCO

synthesist · Posted: Mon Sep 26, 2011 12:50 pm Post subject:

you are right, the voltage drop isnt really noticeable.

by the way,
here is the schematic of the VCO. I used a second cd4046 VCO to feed a pretty high audio range signal into pin 14.

the output sounds like a ringmodulation. a pity that it comes with a constant anoying high tone. I think it's caused by the internal vco. If you turn the potentiometer you can pitchshift the audio input.

there are so many things to do with this IC. The perfect chip for a newbie to start with.

I saw this circuit at a homepage from "flo kaufmann". A similar one is also published in a nicolas collins book.

4046schmo.pdf

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synthesist · Posted: Thu Nov 17, 2011 1:53 pm Post subject:

meow!

I just record something. A super psycho lfo modulates a 4046 vco wich modulates the circuit above.

sounds disgusting!!!
Cool

cd4046_vco_thing_modulated_by_sup.mp3

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CJ Miller · Joined: Jan 07, 2007 Posts: 368 Location: 127.0.0.1

Rule of thumb is that you should not use signals which are less than the VSS/ground pin. So if your ground is actually zero volts, negative voltages coming into the chip can destroy it. I just played with some CMOS chips and powered them from -5V to +5V. So the total supply voltage is 10V and the chip doesn't care what I call it.