[sdiy] triangle hard sync

[Stewart Pye]

Hi David,

Couldn't you just insert a diode in series with your sync signal?
I think the TR808 bass drum does a similar thing, although I think they 
have the diode so that the schmitt trigger point does not affect the 
rest of the circuit it should achieve what you want also. Look around 
the VCO section of the bass drum schematic...
http://www.kolumbus.fi/janne.husu/specs/909va.gif

Regards,
Stewart.


David G. Dixon wrote:
> Hey Team!
>
> I'm trying to retrofit hard sync onto triangle-core LFOs so I can sync them
> with gates, triggers, square waves, etc.  I can get the triangle to reset to
> 0V with a JFET across the cap, but I also want the triangle to start in the
> upward direction every time as well.  I can just about achieve it if I put
> sync spikes into the comparator reference voltage input, but the negative
> sync spikes cause the triangle to reverse direction, which I don't want.
> This wouldn't be a problem if the sync source is a sawtooth, but a square or
> a gate signal would always have negative spikes.  I suppose I could add a
> rectifier to eliminate the negative spikes, but that seems too complicated.
>
> I see that the Oakley VC-LFO does what I want, albeit in the wrong
> direction.
>
> Also, I could probably rig it such that the triangle started at its most
> negative point, in which case it would have to go up.  Perhaps I'll look
> into that next (that might be better).
>
> In any case, if anyone knows how to do this, or can point me to a document
> where I could learn about it, I'd sure appreciate it.  I believe that Magnus
> Danielsson had a relevant document, but the link appears to be dead.
>
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