[sdiy] quadrature VCO - a different approach

[JH.]

> > Still working on my FS-2 project (it goes very slow - most of my spare
time
> > is consumed by that big project of building a house now),
>
> Now, tell us... any neat modules in that project? ;O)

No, it's just a new frequency shifter. 2 channels this time, so it can
either be used
in stereo, or as a chain upshift -> fixed filter (bank) -> downshift to get
some kind of voltage control on fixed filters. This won't be able to shift
full-range audio signals over a wide range, of course, but I reckon it could
be
very useful to slightly move the notches of a comb filter, for instance.


> Have you looked at the Polyphase way of doing things? There is both ideas
for
> the phase-difference-filter as well as for direct oscillators.

I have downloaded this back then, but never read it all. The dome filter
approach
works just nicely. In retrospect, it's no big surprise: 2 x 6 stages make an
excellent
(0.3deg phase error) filter for 3 decades (15Hz ... 15kHz), so with another
2 x 6 stages I can get another 3 decades. It all fits on a 16cm x 10cm
veroboard.

JH.