[sdiy] Sine VCO

[Czech Martin]

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