[sdiy] Gated VCO cycles

[harrybissell]

I did a simulation with the R-S flip-flop.  With a positive pulse to reset
the
VCO, you can do it with one CMOS NOR gate (4001).   The VCO will run a
single cycle (if the trigger pulse is shorter than on cycle) or will run
until
the gate is removed, completing any cycle that is started.

I thnk it would start a sine ot triangle at the peak :^(

H^) harry

harrybissell wrote:

> Peng wrote:
>
> > A gate input where the VCO is off until a gate is received, then it
> > starts it's cycle. when the gate is turned off the VCO finishes it's
> > cycle before going off (see page 7). I want to implement this feature
> > in some of the VCOs I'm building, but I'm not sure how to accomplish
> > this. Should I be looking at the switch in the VCO core?
> >
> > yes.  This should be quite easy with a sawtooth core.  Jam the reset
> > line high with
> > a flip-flop.  Let it go low when you reset it, and let the comparator
> > drive it back high.
> > I'm not positive but I suspect the right polarity of R-S flip-flop
> > would work... when the comparator pulse comes it will still get
> > through to the reset transistor (or fet).
> >
> > This would use the 'disallowed' state of having both set and reset
> > true at the same time. Both outputs will go 'high' then
> >    I'm thinking this gated on/off could solve two problems I have with
> > my synth. One being: how to keep my LFO in time with live impro drums
> > ? For example: I'm using a +/-5V sine to modulate cutoff on a VCF. On
> > every key gate I would like it to modulate the frequency up before
> > (reset). This way, if I get the lfo speed close to the drummers tempo
> > the modulation sounds better (more locked).
> >
> > this might be more like soft sync than gated VCO...  ???
> >    Second problem would be the sharp clicks and pops I get when
> > playing low bass lines, especially when the waveform has low harmonic
> > content, like a sinewave. They kinda come and go randomly with note
> > ons and sometimes note offs. I notice this with other synths with free
> > running oscillators and even a lot of software synths. Are these
> > clicks/pops the result of non-zero cossings (sorry for the sample
> > editing speak)? I can supress the clicks with EQ but that's not always
> > desirable.
> >
> > hmmm... if you used a sawtooth core, and made a triangle with it, and
> > then a sine...
> > the sine wave would always stary at one 'peak' ... exactly the
> > opposite of what
> > you want.
> >
> > Of course you CAN do it... just more complex
> >
> > H^) harry
> >
> >
> >
> >
> >
> >
> >
> >     Any info, advice, comments,ideas are desperately needed and
> > greatly appreciated. ThanksPeng
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