MOTM

> >Craig Critchley wrote:
> >I'm interested in filtering control voltages,

> <media.nai@...> responded:
> Afaik, only the 830, 820, 700, and half of the 110 can process DC.  I
don't
> know about the 130 or 190, even though I've asked a few times.  I guess a
> 320 can be considered a DC processor of some sort -- it has DC inputs and
> can produce a DC output for considerable length of time.

I think only the 820 would be usable for LP filtering control voltages (slow
waveforms).  Of course, LP filtering a flat DC signal would not produce
much. :)

> >Craig Critchley wrote:
> >inspired partly by the '101
> >vibrato circuit and partly by trying to make a PLL with two '300's and
the
> >ring modulator from the '110.

Ok, correct me if I'm wrong, but isn't soft sync basically a form of PLL?

> <media.nai@...> responded:
> My, that sounds ambitious :)  Let me see if I understand what you mean.
You
> are trying to have one 300 track another 300, taking the square outputs of
> both 300's, using a 110 ring mod as a "phase comparator", smooth the
output
> with an 820, then send the output to the second 300 using the FM input??
> Or am I completely lost here??  I think I understand how a "four quadrant
> multiplier" would give the sum and difference frequencies using sines, but
> I don't see how it would give you just the difference like an XOR using
two
> squares.  Wouldn't it give you something much more complex??

Hmmm... The 110 produces both sum and diference sidebands, so when one tunes
both 300s perfectly at 1000Hz, there will be a resultant 2000Hz upper
sideband signal and a DC output corresponding to the difference in the phase
of the two input waveforms.  Now if they're slightly detuned, say by 1Hz,
then the 1Hz low band signal could be retrieved from the output by LP
filtering with the 820.  In any case, I would think the PWM settings of the
two 300s would be critical in this application.  If set to anything other
than precisely 50%, it would add either positive or negative offset to the
LP filtered control voltage.  It could be interesting to try using the PWM
input to control the offset.

Another issue, when using square waves through a ring mod, there are *tons*
of side bands due to all of the odd harmonics present.  Why not use sine
waves?

<snip>

> Regardless whether it works as a PLL or not, that sounds like quite an
> interesting patch!!

Agreed!  I'm curious Craig, what led you to this experiment?

George