[sdiy] Odp: Re: SAW core VCO flyback time

[Ian Fritz]

Cool concept!  I wonder, though, how you make the two ramps exactly the 
same? If they are not, the true fundamental will be an octave lower than 
what you want.  And it will usually be easy to hear, being below the 
fundamental of the individual ramps.

And won't it be hard to buffer the output? You get in trouble with 
ringing, etc. if you try to slew too fast. The output waveform shape can 
be important if you are driving a waveshaper, for example.

But I agree the tracking would be better without the flyback-time 
limitation.

Ian


On 8/27/2016 9:00 PM, Roman wrote:
> One ramp is going up, and when reaches maximum, the MUX switches to 2nd
> ramp, which then starts exactly at this moment.
> Meanwhile 1st ramp is slowly decaying by not-so-fast switch, let's say
> it takes a few microseconds, and is held at 0V untill the 2nd ramp
> reaches its maximum, and MUX switches back again to 1st ramp.
> So reset FETs are not driven by short pulses but out of phase square
> signal. MUX switches between ramps making the reset slope fast as lightning.
> I have this core somewhere in one of my notebooks, or maybe loose paper.
> Never built it hough as it was a bit overkill.
>
> Roman
>
> Dnia 27 sierpnia 2016 19:37 Tom Wiltshire <tom at electricdruid.net>
> napisał(a):
>
>     How would this work, Rick? I'm not seeing it.
>
>     Does it need the two ramps to be running at half the output rate so
>     that you always switch in the middle of the ramp? And don't you just
>     swap flyback time for switching time as the potential glitch?
>
>     Thanks,
>     Tom
>
>     On 27 Aug 2016, at 17:49, Rick Jansen <rick.jansen at xs4all.nl> wrote:
>
>         You could do a dual integrator and alternate their outputs: no
>         flyback time at all.
>
>         rick
>
>
>         On 27/08/2016 18:27, Mattias Rickardsson wrote:
>
>             On 26 August 2016 at 06:42, David G Dixon
>             <dixon at mail.ubc.ca> wrote:
>             > I stopped building sawcore VCOs because I didn't like
>             flyback.  That's why I
>             > only build tricores now, and shape them into saws.  They
>             sound better
>             > anyway, and sync in a more interesting way.
>
>             I'm not a big fan of them either, as far as tracking and
>             waveshaping
>             is concerned.
>
>             But regarding the sound - I made a very bad (meaning slow
>             flyback) saw
>             core, and now people shout that it sounds so great and they
>             want it in
>             more designs.
>
>             Alas, the ever so unrewarding nature of good engineering! ;-)
>
>             /mr
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