SV: [sdiy] QVCO schemo up

[JH.]

> >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.
> 
> Looks interesting.  Aren't there problems with the 633 as far as offsets?

I've built four AD633-based Ring modulators with a full set of offset pots,
and in the end I found I "almost" wouldn't have needed them.
If memory serves, the 2nd harmonic bleedthru was bigger than the
fundamental (which you trim with offset pots), and both were as low
as a carefully trimmed dual-OTA ringmod that had trimmers for
fundamental- and 2nd harmonic bleedthru supression. Quite
impressive, that AD633.

But with these good results from your circuit coming in, I doubt 
that I'll build that expensive multiplier-based one. (Except this
might give even lower THD figures.)

Tonight I did neither - I was working on the final mix of one
track that will go onto my new CD.  8-)
As Tracktion was rendering tracks, I typed some emails.

JH.