[sdiy] Adding "sync" to a Through-Zero Sinewave Oscillator design

David G Dixon dixon at mail.ubc.ca
Sun Sep 16 08:45:06 CEST 2018

The Intellijel Rubicon 2 is a through-zero VCO which I designed, and it has
both kinds of sync.  We call them "Hard" and "Flip" on the panel, but I
always think of them as "Reset" and "Reverse".  The Resetting sync is
achieved in the normal way, with a JFET across the integrator capacitor.
The Reversing sync is achieved by syncing to the threshold input pin of the
comparator in the tri-square core.

> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On 
> Behalf Of Donald Tillman
> Sent: Saturday, September 15, 2018 10:31 PM
> To: ulfur hansson
> Cc: synth-diy mailing list
> Subject: Re: [sdiy] Adding "sync" to a Through-Zero Sinewave 
> Oscillator design
> > On Sep 15, 2018, at 3:26 PM, ulfur hansson <ulfurh at gmail.com> wrote:
> > 
> > I love the way traditional triangle core oscillator sync 
> sounds, and much prefer it to the harsher sawcore type sync.  
> with trianglecore sync (I hope I understand this correctly) 
> the waveform changes sign at trigger points rather than doing 
> a hard reset to 0v, right?
> There are several way to sync a triangle wave.
> The technically correct way would be to force the oscillator 
> to the start of the waveform.  So if it's advertised as a 
> sine wave, the sync pulse should bring it to 0V, ascending.
> I'll claim that reversing the direction of the wave is not 
> actually a sync.  The word "synchronize" means to bring an 
> oscillator to the same frequency, and same phase, as another. 
>  I don't think that's remotely possible by flipping the 
> direction of the triangle every cycle.
> I'd even call it "anti-sync".
> But if it's an expressive sound, it's probably worth coming 
> up with a better name.
>   -- Don
> --
> Donald Tillman, Palo Alto, California
> http://www.till.com
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