[sdiy] VCO sync question

[Oakley Sound]

> my CGS/EN VCO would only sync to rising ramp or inverted pulse (I don't 
> know why).

Maybe its to do with falling edge timing. Obviously a ramp waveform has a 
fast falling edge, particularly if this is the waveform generated by a 
VCO core, and so should a pulse. But it could be that this is not the 
case if you generate your pulse with a non symmetrical circuit. Perhaps 
the falling edge is not fast enough to reset the comparator.

A simple schmitt trigger should sharpen up those edges nicely.

The other thing to consider is that the pulse output may be loaded by the 
capacitive input on the sync input. This can cause waveform distortion 
from a high impedance output [over 1K] and produce the unwanted slewing 
of the falling edge.

Tony

www.oakleysound.com