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

[Roman]

That's the point - they don't have to be identical!  I thought about it right after shutting down computer yesterday. You can even tune one integrator an octave higher or more than other to get nice sub-oscillator-like sounds. But anyway, if they are just slightly mismatched, the result will be not as octave lower dominant, but as slight touch of a suboscillator, definitely more interesting sound, than regular saw.   The idea is to use 2 identical integrators made of the same parts, instead of one going up and one going down, because it's easier to make them identical. 1% capacitors are common and double output expo pair can be made of 3 transistors on the same LM3046 chip for example. At that level of repeatability it would be not easy to hear the octave-down part.  But the fun starts when you intentionally mismatch them, or even allow duty cycle modulation between 2 integrators. Of course to keep this in tune while cycle-share-duty CV modulating is not that easy as requires reciprocal of CV and that part may introduce additional errors and thermal drift.   As for buffering - if it goes straight to waveshaper, so that connection will never change, it's possible to make it good enough, keeping the ring/overshoot shorter and smaller than waveshaper can react. But for pure saw output provided as jack on the module, where anybody can plug any kind of unknown cable, it would be wise to filter it down a bit before it leaves the PCB.   Roman  Dnia 28 sierpnia 2016 19:17 Ian Fritz <ijfritz at comcast.net> napisał(a):
                  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  ______________________________  Synth-diy mailing list  Synth-diy at dropmix.xs4all.nl <mailto:Synth-diy at dropmix.xs4a  dropmix.xs4all.nl dropmix.xs4all.nl    ______________________________  Synth-diy mailing list  Synth-diy at dropmix.xs4all.nl <mailto:Synth-diy at dropmix.xs4a  dropmix.xs4all.nl dropmix.xs4all.nl    ______________________________  Synth-diy mailing list  Synth-diy at dropmix.xs4all.nl <mailto:Synth-diy at dropmix.xs4a  dropmix.xs4all.nl dropmix.xs4all.nl      ______________________________  Synth-diy mailing list   Synth-diy at dropmix.xs4all.nl  dropmix.xs4all.nl dropmix.xs4all.nl     --   ijfritz.byethost4.com
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