[sdiy] 555 cv level?/Psuedo Random Generator Circuit..wow/questions

[Dan Snazelle]

here is the fixed link

http://www.media.mit.edu/physics/pedagogy/fab/electronics/assignment.html

a very interesting circuit. I am experimenting with adding external control voltage to the clock oscillator (which is the 2nd half of the 556)

i have tried replacing the 556 vco with an external vco but only other +5v sources (like a 40106 i tried) seem to work.
I need to find a way to level shift or buffer signals that come from +/-12 volts to work with this. it seems stuff that is running on a higher voltage WILL NOT work properly with this unit.

any ideas on how to achieve proper buffering?

thanks