[sdiy] VCO idea

[Theo]

As Ian explained your only fire a SH, so if I get this correctly you only
use the 3419 outputs to trigger a short pulse.
The "new" stage will trigger the pulse for the SH, the "old" stage being
still active doesn't matter.

As for the CPU with A/D option, digital is _ALWAYS_ better ;^p

Theo


From: charlie lamm <charlie at www2.charlielamm.com>


> How exactly to make the "VU" in question does seem to be a problem....
> Yes, as I see it, I need only one "LED" active at a time for this to work.
>
> Hmm, I wonder if this is a job for a CPU....with an A/D convertor or
> onboard A/D sampling the amplitude of the incoming signal and switching
> its line low and high accordingly.
>
> Might be easier than trying to do it with a lot of components, but maybe
> not cheaper....
>
> Anyway, thanks for all the input.  I have to finish my ASM PCB and then
> that may be the next thing I work on.  Whatever I come up with I will
> share w/ the group....
>
>
> On Mon, 13 Jan 2003, Theo wrote:
>
> > Problem with the LM3914 it that there are TWO leds/outputs active when
> > switching to the next stage. This may or may not be a problem with your
> > application.
> > For building a quantizer I tried adding positive feedback to pull the
input
> > voltage out of the "two led" range. For my quantizer this was not a good
> > solution because it only worked ok with a rising input voltage. A
falling
> > input voltage still made two outputs to be active at the transition
points.
> >
> > Cheers,
> > Theo
> >
> > From: Ian Fritz <ijfritz at earthlink.net>
> >
> > > Charlie --
> > >
> > > Sure, that'll work. And, as you guessed, it's been done.
> > >
> > > A simple way is to use the LM3914 LED bargraph chip. It has the
> > comparitors
> > > built in, and it can be wired to just fire one output at a time.
> > >
> > > I built a 16-stage sequencer once upon a time using a pair of cascaded
> > LM3914s.
> > >
> > > For a current example, which is actually closer to what you are asking
> > > about, I have a circuit that uses a LM3914 to fire a bank of S/H's to
form
> > > a delay unit.  It's part of my analog physical modeling experiment.
> > > http://home.earthlink.net/~ijfritz/pm_cir3.htm
> > >
> > > I've always thought the LM3914 has many interesting musical
applications,
> > > but not all that many have been developed.  With some imagination and
an
> > > accurate VCO (watch that flyback) you can implement  all kind of
clever
> > > devices.
> > >
> > > Let us know if you work on this further or have further questions on
the
> > > LM3914.
> > >
> > >    Ian
> > >
> > >
> > > At 05:46 AM 1/13/2003, you wrote:
> > > I woke up this morning with what I thought was an interesting idea for
a
> > > VCO...that has probably already been done by someone else.....
> > >
> > > --Start with a sawtooth "core" VCO.  The ASM-1 or equiv; any simple
> > > accurate 1V/oct VCO, you don't need any pulse stuff, just the
sawtooth.
> > >
> > > --The sawtooth output should run from peak (say, 10V) to 0V DC during
> > > each cycle.
> > >
> > > --The output of the core VCO goes to a series of 8-10 resistors
(accurate
> > > ones, say 100K 1%) arranged in a giant voltage divider ladder.
> > >
> > > --The output of each junction of the ladder goes to a comparator
(LM311?
> > > LM6511?) and some sort of AND gate subcircuit that traps when there is
a
> > > "match" between the sawtooth's output voltage and the particular stage
of
> > > the voltage divider the LM311 is tied to.  So you are building a VU
> > > basically, but unlike a VU meter, only a single "light" is shown at
any
> > > given time, that lights up to show the current DC voltage of the
sawtooth.
> > >
> > > --Now, the output of each "stage" of the VU-like device hits a sample
and
> > > hold.
> > >
> > > --The "hold" on each S/H is re-triggered by the previous or next stage
of
> > > the VU ladder.  For added fun, make this adjustable; each S/H's "hold"
is
> > > triggered by whatever rung in the ladder you want.
> > >
> > >
> > > --As far as what to "sample" for each S/H, you could use DC voltages,
> > > giving you (hopefully) analog-sounding waveforms.  For instance, I see
a
> > > group of 8-12 sliders.  Each slider is hooked to the input of a single
> > > S/H.  Each slider is a voltage divider.  In practice: The first 3
sliders
> > > set all the up and the others all the down would give you a narrow
pulse
> > > wave. A sine-wave looking knob setup gives you a close to sine wave
> > > output.
> > >
> > > -- Or you could use AC stuff, other outputs of VCO's, noise, whatever,
> > > feeding the different inputs of each S/H giving you (I don't know I
would
> > > guess) ring-modulator sounding stuff.  You could use slowly sweeping
DC's,
> > > giving you (I have no idea what it'd sound like).
> > >
> > > --Here is what I'd hope: the output frequency of what's above is
> > > determined by the frequency of the sawtooth.  In other words, the
whole
> > > thing should stay in pitch with the original frequency of the waveform
> > > generated by the core VCO.
> > >
> > > --Now, you'd need some way to "demux" the outputs each S/H.  Into a
single
> > > audio signal.  That's your audio output.  Haven't figured this one out
> > > yet, but I have a feeling it's doable.
> > >
> > > Which leads me to questions for the synth-diy menches:
> > >
> > > a) Does this make any sense?
> > >
> > > b) Will it "work"?  Am I wasting my time because the above scenario is
> > > massively flawed from the standpoint of what can and can't be done
> > > electronically?
> > >
> > > b') Assuming I can make the above work, can anyone speculate if it
will it
> > > be "musical" in a traditional sense?  IE: will the above scenario
never
> > > stay in tune, making it useful for only atonal, avante-garde (as
opposed
> > > to western sounding, 12 semitones an octave) stuff?
> > >
> > > c) Assuming it can be done, someone must have already thought of this,
and
> > > someone must be already doing this.  To me it seems like a simple
idea.
> > > If so, I'd like to see the schematic to see how he or she has pulled
it
> > > off.  Maybe someone can suggest a link....I figure I could learn a lot
> > > studying that schematic and/or circuit design, and may want to
incorporate
> > > it into the synthesizer I am building now.  EG: I see an analog shift
> > > register on Ken Stone's site that has the same sort of S/H thinking of
the
> > > above, but is clock-controlled, not VCO sawtooth controlled, and has
less
> > > stages.....http://www.cgs.synth.net/
> > >
> > > Sorry about the length of this post....hope I have made myself clear.
> > > Thanks in advance for all the help....
> > >
> >
>