vco radical

[Martin Czech]

Someone wrote about vco sync ideas some time ago.
Many industry synths have no sync at all, or poor versions.

That's why DIY. Take it to the limit.

Well, here's my idea about that :

Consider a saw oscillator.
Current source, cap, discharge trany, low leakage mosfet-schmidt-trigger,
mosfet unity gain opamp.
I'll try to connect the schmidt directly to the timing cap, this should be
fast, though low leak.
(Is this "classic" kind of circuit more acurate than more complicated triangle
oscs ? I guess so, the less components, the less error, or what ?
Any experience out there ? It'll take some time for me to find out allone).

Add a second transistor to discharge to voltage controlled level.
That is, the sync-jump point is now voltage controlled,
or more technically : the sync phase.
=> parameter sync phase
Now, one could add some trigger logic, in the general case this will
lead to a window comparator, I think.
So, syncing will only be allowed, if the saw wave is in the predetermined
window (the phase is in window).
So one can change the characteristic from hard sync (window wide open,
always sync) to "soft" sync (window small and near max{saw}), and
all in between.
=> parameter window position, window width

Triangle oscillators offer another possibility: change of loading
direction in case of sync, that is the comparator flip-flop 
is toggled by the sync pulse. The CEM oscs had this feature 
but they could not "jump" to a sync level instead.

Hmm, I also want this feature of direction inversion in my saw osc,
(because of my BELIEVE that tri oscs cause more trouble,, maybe
I'm wrong here).
This is possible, if the sync-jump point depends on the actual
saw wave value (inverted with some offset).
Rectifying the saw gives the desired tri with direction inversion.
=> parameter saw/tri sync

Now I've got a saw osc with very flexible sync options (did I forget
any sync option ?), no complicated circuitry, no additional expensive 
parts. Ok, a bit more leakage current, due to the second discharge
transistor. 
4 new parameters to toy with...
This will lead to more knobs and jacks on the
panel, so I will drop ALL waveform converters, keep just saw output. 

All the converters will be external modules, so I can also
feed any waveform of my synth into them.

m.c.