[sdiy] Saw vs Triangle Sync

[David G. Dixon]

> >What you describe (if I'm not mistaken) is what I do with all my VCOs,
> >simply by putting an attenuator on the sync input.  This varies the
> height
> >of the sync pulse which, if less than 5V (in my case), MAY OR MAY NOT
> reset
> >the oscillator, depending on the amplitude of the wave when the sync
> pulse
> >is presented.  That works on both core types.
> 
> Seems like the same thing, though I defer to those with superior
> knowledge. (Ian? Barry?) The soft sync input on a Synthesizers.com
> VCO does have a level control, though I'm not sure whether it
> attenuates the input or sets a threshold voltage in the sync comparator.

In my case, there is no sync comparator, per se.  In my Tricore, the sync
pulses are summed with the integrator output in an inverting summer, and the
resulting output is what fires the schmitt trigger which flips the triangle.

In my Sawcore, I've passively added the sync pulses to the 5V reference at
the (-) input to the saw comparator.  This is "legal" because the 5V
reference is ac ground.  The circuit looks like this:

Sync in -- 10k atten. -- 3.3nF cap --|-- (-) input to saw comparator
                                     |
                                     |-- 1k resistor <-- 5V (ac ground) 

When the attenuator is cranked all the way up, I get hard sync, as the
pulses are about 10V.