[sdiy] Dual oscillator cores?

[Jerry Gray-Eskue]

<<I'm not sure how triangle cores
switch the direction,>>

Take a look at this, it is near to a classic Integrator / Comparator setup
and may help clear up how triangle cores operate.

http://www.musicfromouterspace.com/analogsynth/NewAugustRampLFO.html

- Jerry

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of cheater cheater
Sent: Monday, October 19, 2009 4:23 AM
To: synth-diy
Subject: Re: [sdiy] Dual oscillator cores?


Don,
Thanks a lot for your reply. Very interesting!

I hadn't had time to finish reading the article thoroughly, since I
was moving last weekend :^) but it's very, very interesting judging by
what I've read. I wonder if there are any audio examples to be had?

Regarding the triangle core designs: I'm not sure how triangle cores
switch the direction, but I presume that for example when switching
from rising to falling that the core has to be *disconnected* from the
positive current source and only when that is done connected to the
negative current source, right? I would understand that in real-world
terms this means some form of delay between the 'disconnect' moment
and the 'connect' moment, but of course I'm not a solid state
engineer. It would seem like this could be a much shorter time than a
saw core flush though. This is just pure speculation on my part..

Ian,
of course you come back to us with something you've mentined already
and I just didn't pick up :) thanks a lot for your suggestion, you're
truly invaluable sometimes!

Seems like a multicore design could be a fairly interesting way to do
stuff after all.

Thanks all
D.

P.S. CPUs have multicore designs... so why couldn't we have them in
oscillators? ;-)

On Sun, Oct 18, 2009 at 8:02 PM, Donald Tillman <don at till.com> wrote:
>   > Date: Sun, 18 Oct 2009 19:27:55 +0100
>   > From: cheater cheater <cheater00 at gmail.com>
>   >
>   > great pointer with regards to Don Tillman. He uses two
>   > accumulators for a different reason obviously, but it's still
>   > related.  I think because of that design he ends up avoiding the
>   > HF problems as well, right?
>
> Hi.
>
> Yes, indeed.  All cores that take a break from the integration
> operation for a quick reset will suffer the HF slip.  (Some
> compensation in the exponential converter is possible, of course.)
>
> So a triangle core does not have the HF slip.
>
> And my Quadrature Trapezoid core does not have the HF slip.
>
> And the Rhodes Chroma VCO that uses a charge pump to propotionately
> reset the integrator does not have the HF slip.
>
> And the Aries VCO with two cores (*** hey, the original question!)
> running simultaneously, one triangle and one sawtooth, does not have
> the HF slip.  (Does somebody have a pointer to a schematic for
> that?)
>
>   > After all he can switch the a core to the 'stopped' state
>   > instantaneously, and then switch it to the 'reverse' state
>   > instantly as well. He doesn't have to wait for the action of
>   > switching from forward to reverse (which obviously can't happen
>   > instantaneously - otherwise we'd end up shorting opposite voltage
>   > rails). Very interesting. And he makes it work with thru-zero FM
>   > as well! Neat!
>
> Yes.  And it provides quadrature outputs.
>
>   > The next question is of whether and how you can find a matched
>   > pair of capacitors =)
>
> It's pretty easy to match capacitors by hand.  And the worst problem
> with unmatched capacitors in the QuadTrap VCO is that the duty cycle
> will be slightly off from 50%.  That's not horrible; nobody gets hurt
> or anything.
>
> However... in your original two-core proposal, unmatched capacitors
> will cause alternate cycles to be different lengths, so you'll have
> some subharmonic content there.  That could be more of an issue.
>
> -- Don
>
> --
> Don Tillman
> Palo Alto, California
> don at till.com
> http://www.till.com
>

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