[sdiy] sync on a triangle core vco?

David G. Dixon dixon at interchange.ubc.ca
Sun May 17 20:53:17 CEST 2009


I modified the Thomas Henry VCO-1 triangle core for sync.  In that case, I
intercepted the buffered triangle output on its way to the discrete schmitt
trigger and put it through an inverting unity-gain summer.  To this summer I
also added a sync input through a passive high-pass filter to convert it to
spikes.  Hence, either a saw/ramp or a pulse wave can be fed to the sync
input -- anything with sharp edges.  Since the schmitt trigger flips at
+/-5V, it will reset whenever the pulse plus the triangle equals or exceeds
this voltage.  I put the sync input through an attenuator to get spikes of
varying height, and this makes the sync less likely and gives interesting
harmonic effects.  However, because I inverted the triangle on its way to
the trigger, I had to switch the inputs at the current-sourcing OTA to
correct the polarity.

I don't have a website, but I'd be happy to send anyone who is interested a
copy of my schematics in .pdf format, along with the original VCO-1
schematic for comparison purposes.  I can say that either version of the TH
VCO-1 works exceedingly well, and I'm also very pleased with the sync

> this is something i have been wondering about
> i know you can do it on a sawcore by injecting a pulse into the cap. but
> what about in a tri core? i do not understand WHERE it would go and i cant
> think of any schematics off hand that have this feature

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