[sdiy] Ken stone's synthacon filter

[Roy J. Tellason]

On Sunday 12 September 2004 01:33 pm, Karl Ekdahl wrote:
> I found something very strange in my circuit; i use a
> SPST switch and a 4066 + 4001 to select HP, BP or LP
> mode. That is configured something like this (bad
> ascii art coming up):
>
>              / o---o------------o HP (to 4066)
>    +9v ----o/ SPST |
>                o-o--------------o LP (to 4066)
>
>                  | |    ___
>                  |
>                  | o---\   `.
>                  |
>                  |     | NOR >--o BP (to 4066)
>
>                  o-----/___,´
>
>
> and then delivered the signal through the 4066 to the
> VCF. The thing is that starting of at the BP mode (no
> switch active) works. But while switching to another
> mode, there's a loud *click* and the circuit dies.
> Switching back to BP mode and direct-injecting a
> high-level signal into the circuit makes it run again.
> Being in LP or HP mode and direct-injecting doesn't
> give any results whatsoever. Funny thing is that it
> also died while turning of my soldering iron and i
> made it take in radio as well.
>
> Any thoughts?

You don't show any resistors going to the gate inputs that are connected to 
that switch...

The switch supplying +9 volts,  you should have some resistors to ground in 
there.  NEVER leave a CMOS gate input "floating",  weird stuff happens.

For a much more detailed treatment of how to use these parts see if you can 
snag a copy of Don Lancaster's CMOS Cookbook.