[sdiy] High frequency VCO as BBD clock

[Neil Johnson]

Hi,

René Schmitz <synth at schmitzbits.de> wrote:
>
>
> Am 07.02.2023 um 19:18 schrieb Rutger Vlek via Synth-diy:
> > Dear list,
> >
> > For a while I've been working on a guitar pedal board for personal
> > use. I'm about to build the second revision of a solid state pre-amp,
> > and was thinking about possible modulation effects too. I would love a
> > nice (stereo) BBD flanger/chorus, but felt a bit fed-up with all the
> > 'classic' designs, particularly the traditional clocking scheme,
> > usually with a limited range, lack of current drive (to overcome
> > capacitance of the BBD clock input) and strictly linear modulation
> > (calling for a hyper-triangle modulation source).
> >
> > Having some experience with designing saw- and tri-core VCO's around
> > the 2164, I was wondering how easy it would be to push the design of a
> > typical tri-core VCO with an 2164-based expo converter into higher
> > frequencies (let's say up to 500kHz) and use it to clock a BBD? Has
> > anyone tried? Or are there fundamental reasons why such frequencies
> > are not possible? I've never (intentionally) worked with circuits
> > outside of the audio bandwidth...
> >
> On the 2164 there is typically a 500 ohm + 560p  RC at the input that
> delimits the bandwidth. That chip has a mere 500kHz to begin with. One
> would have to see if the chip is fast enough to be accurate at that speed.
>
> There is a VCO circuit with a CA3080 in the datasheet that is claimed to
> be working up to 1Mhz.

Probably best to use a linear high frequency VCO and the 2164 as the
expo converter.  Plenty of brilliant examples in Jim Williams's AN-14
application note.  Or look at the various linear V-to-F chips (e.g.,
TI VFC32).

Neil