SV: Re: SV: [sdiy] QVCO schemo up

[harrybissell]

LOL.

Yes...and no

AD633, forget it

Spice model for the LM13600/13700 has good convergence with actual
real life parts. Activating the diode linearizarion always makes my offset
problems worse. Some 13600/13700 are much better or worse than others.

I agree with your result of removing the diode bias. With both removed, I get
rounded triangles. I did not try just ~one~ removed.

H^) harry

karl dalen wrote:

> Forget the Ad663 stuff, Ians cirquit works gerat! :)
> Also, trow away SPICE, digital simulations just give you voltage offsets! ;-)
>
> Reg
> KD
>
> --- "JH." <jhaible at debitel.net> skrev:
>
> > > I SPICE simulated it, already. It works well
> > > as advertized.  DO NOT try it with a 3080
> > > it will generate quasi-triangle waves. You need
> > > the LM13700 (or 13600 I presume) with the diode
> > > linearization.
> > >
> > > I did get offset on the two waves in opposite
> > > directions. I have not 'trimmed' the simulation.
> >
> > That's what I get with _every_ QVCO based on
> > OTAs in simulation. Must be the offset voltage.
> > I _hope_ the THAT VCAs would solve this problems
> > (if they work in this application, that is.)
> >
> >
> > > It takes hundreds of cycles to come up to stable
> > > amplitude. I suspect this will be similar to an old
> > > Wien-bridge oscillator which takes a long time to
> > > stabilize after a frequency shift, but I didn't
> > > simulate that, yet.
> >
> > Ok, this might be the catch then. I hope it's not,
> > but it makes sense. Very weak gain correction,
> > low distortion, but long reaction time.
> > If it only has to react to gain drift, no problem.
> > If for some reason it has to react to a frequency
> > change (why would it, btw?), then FM on such
> > a VCO would be a problem.
> >
> > I've posted a drawing (simulated, but not tested) of a
> > possible version of the QVCO from Tietze/Schenk
> > here:
> > http://www.oldcrows.net/~jhaible/matrix_fx/jh_ts_qvco_idea.pdf
> > They have drawn it with analog computer building blocks,.
> > which I changed to AD633s and THAT VCAs.
> > They advertise this circuit for being frequency modulated
> > without amplitude effects, as opposed to FM'ing LC
> > oscillator.
> >
> > It's not as elegant as Ian's original circuit. It could be
> > quite small, too (compared to the waveshaping stuff
> > I presented some days ago), but quite expensive.
> >
> > JH.
> >
> >