[sdiy] Dual oscillator cores?

[Harry Bissell]

http://www.leinermedia.net/aries/AriesSchematics/AR-317s.gif

The sawtooth core is reset from the triangle... so think of it as
a hard-sync'd core.  Errors will show up as variation in the sawtooth
amplitude.

H^) harry



----- Original Message -----
From: Donald Tillman <don at till.com>
To: cheater cheater <cheater00 at gmail.com>
Cc: synth-diy at dropmix.xs4all.nl
Sent: Sun, 18 Oct 2009 15:02:28 -0400 (EDT)
Subject: Re: [sdiy] Dual oscillator cores?

   > 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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-- 
Harry Bissell & Nora Abdullah 4eva