[sdiy] Sine VCO

[Theo]

Yes this method can do ok :)
I have a schematic for this some where using one 4051 like switch for a "32
sample sine".
Its not a VCO but a  AM modulator for high quality audio transport over long
lines (think miles).
It performed very well, with minimum components, 4 ICs or so for the whole
thing.
No VCA needed, as the audio feeds into the voltage dividers of the sine
generator.
See if I can find.

On a related topic.
I am doing a FM-LFO module using a FM modulate-able tri wave core.
This tri core changes the "phase" of the oscillation when the CV input
changes sign.
The problem I run into is that when the CV input happens to change sign
at the same time as the flip flop for the timing cap changes from charging
to discharging
the cap keeps charging until it hits the rails.
Same can happen when discharging.
Any suggestions?

Cheers,
Theo


----- Original Message -----
From: Czech Martin <Martin.Czech at Micronas.com>
To: Michael Zacherl <sdiy-mz01 at arsprototo.at>; Rönnberg, Niklas
<nikro at itn.liu.se>
Cc: <synth-diy at dropmix.xs4all.nl>
Sent: Friday, March 28, 2003 11:22 AM
Subject: RE: [sdiy] Sine VCO


> Yesterday I read another old article about stepped
> sine wave approximation. It was actually a chip,
> called FX205 or so. The idea is that of a sequencer,
> spitting out a step function. If you scale these
> steps in a proper fashion, you can eliminate
> 2nd, 3rd and perhaps some other harmonics,
> i.e. those that hurt most. The rest can be filtered.
> Ahhh, stupid, all even harmonics are absend...
>
> I think the article said that only the 7th, 9th and higher
> harmonic is present.
>
> Using linearity properties it shouldn't be too
> hard to figure out the proper weigths.
>
> Perhaps the sequencer should make use of symmetry,
> i.e. forward-backward counter with sign flipper.
> This can reduce the number of weigths, i.e.
> pots to turn.
>
> m.c.
>
> -----Original Message-----
> From: Michael Zacherl [mailto:sdiy-mz01 at arsprototo.at]
> Sent: Freitag, 28. März 2003 10:52
> To: "Rönnberg, Niklas"
> Cc: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Sine VCO
>
>
> Hi,
> I'd be interested too!
>
> Since a waveformconverter for a good sinewave is
> rather componentintensive a set of "classic" VCOs
> for additive synthesis would be expensive (IMHO).
>
> Besides linear FM (err .. did you mean linear?)
> are you looking for Oct./V characteristics as well?
>
> How about modifying the charge/discharge part of
> the sawtooth circuit, to get a triangle instead of
> a saw and to smoothen it out afterwards?
> (Just a rough, ugly, untested thought).
>
> How clean do you need this sine wave? Has it to be
> an ideal one?
>
> have a nice day,
> Michael.
>
> Rönnberg, Niklas wrote:
> > I'm looking for a sine VCO. I don't want (or need) any other waveform
from
> > this VCO, but I guess that that is unavoidable. I also want the VCO to
have
> > an input for FM...
> > I think that I saw a schematic once that was based on a LM13600. This
VCO
> > made a triangle wave, so maybe this would be a good start for a sine
> > VCO(?).
> >
> > Can anyone help me pointing out a schematic or giving a tip on designing
> > this circuit?
> >
> > Regards,
> >
> > Niklas
>
>