[sdiy] OOOOPS!!!! (Top octave CPLDs)

[Tim Ressel]

Hello other Tim,

We're getting into Hammond territory here. While I can
add dividers, it will wind up adding a third CPLD, or
changing to a larger, more expensive CPLD. CD4024s are
way way cheaper.

So like, are we talking polyphonic here? I assume we
are.

One totally crazy idea I had is to do the Lancaster
trip, but use the diode VCA thing to control the
mixing. Then we approach the Hammond trip.

No, changing duty cycle in the current design is not
possible. I could change the design, but it will take
more room, and that means less notes per package, and
that means more chips and more money.

So like, I'm going with the 3-octave divider thing for
now. I can always make different designs later.

Another wild and crazy notion is a true Hammond
digital tone generator. This would be what Hal
Chamberlin's book called a 'Forier Generator'.
Basically a digital sine wave tone bank with
adjustable freqs and amplitudes. But at is for another
day.

--TR


--- Tim Parkhurst <tparkhurst at siliconbandwidth.com>
wrote:
> Halloo OT (Other Tim),
> 
> I was sort of thinking of summing different squares
> through resistors to
> make a saw wave (the Don Lancaster method). I was
> also poking around with a
> design (on paper) the other day that takes a saw and
> uses four comparators
> to make four independent pulse waves (very simple,
> I'm sure it's been done
> before). If you tweak the duty cycles and mix these
> together just right, you
> can get very close to a saw. 
> 
> Perhaps a nice addition might be to allow switching
> between two or three
> different duty cycles. Is that possible with your
> design? It wouldn't make a
> nice smooth transition, but it would add a little
> versatility.
> 
> Tim Servo
> 
> ************************************
> > -----Original Message-----
> > From: Tim Ressel [mailto:madhun2001 at yahoo.com]
> > Sent: Wednesday, October 30, 2002 5:32 PM
> > To: Tim Parkhurst; synth-diy at dropmix.xs4all.nl
> > Subject: RE: [sdiy] OOOOPS!!!! (Top octave CPLDs)
> > 
> > Hey other Tim (and all),
> > 
> > The TOG project consists of two chips, each one
> > handling half an octave. This is because of the
> way I
> > do the generation, and due to size constraints. I
> use
> > a comparator to create the output wave. This
> allows
> > duty cycles other that 50/50. The original MK50240
> > came in a 30/70 version; I wanted to keep that
> option.
> > In fact, mine can to any duty cycle. The down side
> is
> > the duty cycle is hard-coded in the chip.
> > 
> > I will be offering the chip set for sale. Price
> for
> > the two chip set + sockets will be $20 + $5 S&H
> > 
> > --TR
> > 
> > As far as summing pulse trains to make saw waves,
> I'm
> > not sure how that would work. I've seen the Don
> > Lancaster method of making saw waves by summing
> 50/50
> > square waves with resistors, and I've seen the
> > Simonton design making narrow pulses by gating
> > together 50/50 square waves. Are you talking about
> one
> > of these? Is there a schematic I can look at?
> > 
> > --TR
> > 
> 
> 
> 
>
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