Switching a Red Llama with a cd4066

[bubish]

First Post!  WooHoo!

Now that that's out of the way, I am building a Red Llama, and would like to use a cd4066 for switching as described here: http://www.geocities.com/thetonegod/switches/switches.html.
Can I use the unused inverters on the cd4049? Or will that mess with the proper operation of the distortion circuit.

I realize that it would be easier to just use a 3PDT foot switch, but I only have a SPDT laying around, and I scavenged a cd4066 from an old CD player.

Thanks!

[gez]

Can I use the unused inverters on the cd4049? Or will that mess with the proper operation of the distortion circuit.

Presumably, you'd use the inverters for a latch to control the switching (4066).  Not a good idea IMO as all the inverters within the chip share the same power connections.  It's likely that you'd couple switching noise through to the audio chain.

[bubish]

I guess that's why they are left unused
Thanks for the help!

[earthtonesaudio]

First, welcome to the forum!

Second, Gez is correct that the switching spikes will couple into the audio circuit.  However, there are certain ways of arranging the power supply that will make it much less noticeable.  If I recall correctly, the Llama has a resistor between +9V and the 4049's power pin.  This resistor effectively makes all the inverters "less isolated" from each other, and will make crosstalk worse.  If there's a large value cap from Vdd to ground, that will reduce crosstalk, maybe enough that you won't notice it.
Even better, if the power supply goes through a 5V regulator and has a big cap from Vdd to ground.

CMOS inverters are pretty low current devices (especially at 5V), and that's a good thing for minimizing supply line-coupled switching spikes.  Try it on the breadboard, it might work.

Personally, I'm the type who will go to extremes just to use every last CMOS inverter on a 4049, so take my advice with that in mind.   

[gez]

If I recall correctly, the Llama has a resistor between +9V and the 4049's power pin.  This resistor effectively makes all the inverters "less isolated" from each other, and will make crosstalk worse.  If there's a large value cap from Vdd to ground, that will reduce crosstalk, maybe enough that you won't notice it.
Even better, if the power supply goes through a 5V regulator and has a big cap from Vdd to ground.

Good points.  An inverter's 'Class A' current is still relatively high at 5V, though, and you can decouple all you like but there are internal connections that share the same rails so some bleed-through is inevitable.  True, by minimising current (reducing supply), you'll get to the point where spikes will be (pretty much) inaudible/greatly reduced.  That would be around the 3V mark, though (as mentioned in the Art of Electronics), and CMOS distortions sound pretty awful running at that voltage in my experience (your ears may tell you otherwise). 

CMOS inverters are pretty low current devices (especially at 5V), and that's a good thing for minimizing supply line-coupled switching spikes. 

Relatively low at 5V (slightly less than 1mA per inverter), but not so at 9V (a few milliamps per inverter with some chips).