[sdiy] Overdriving 4069UB

[Seb Francis]

Well, I've been getting some really nice results with using between 1 
and 3 stages of a 4069UB for distortion.  The MOSFET clipping has a 
really warm sound to it.  (Incidently the 4049 really wasn't so good - 
the clipping was way too asymmetrical.)  Anyway, more on this later .. 
I'll publish the final circuit in due course.

What I'm concerned about in my circuit design is whether it is safe to 
drive the 4069 beyond its absolute maximum input voltage.  The quoted 
absolute maximum range is -0.5V to VDD+0.5V (VDD=15 in my circuit).

The input current is limited by a 10K resistor (with a DC blocking cap 
in series before it), so although the opamp driving it can kick out up 
to 28V ptp, the voltage at the 4069 input gets clipped to approx 17V 
ptp.  This is a bit beyond the quoted absolute maximum, but I guess as 
long as the current through the internal protection diodes is limited by 
the 10K resistor then this is ok??  Is this a safe assumption?

Seb