[sdiy] High frequency VCO as BBD clock

[Rutger Vlek]

Hi Tom,

Nice to see you reply! Your website's info on BBD's was a joy to read, and
your digital solution to covering both the lfo and clock circuits is my
fallback for when it does not work out in the analog domain. For another
project I just ordered a stomplfo IC, so will enjoy your work in any case.

As for flanging, it would be nice if it could be achieved without the need
for a separate BBD with fewer stages (that would not work well for
chorusing), hence my interest in pushing to higher frequencies, so that I
achieve chorus and flanging with the same BBD.

I already glanced at the DoubleDeka design mentioned earlier in this
thread. Great idea, though involving a very expensive part! I was hoping to
find a cheaper way. Exponentiating with the 2164, and feeding an integrated
linear hf VCO is perhaps my best option? And then buffering the output to
obtain sufficient current drive if needed.

Rutger



Op di 7 feb. 2023 21:14 schreef Tom Wiltshire <tom at electricdruid.net>:

> Yes, BBDs are still produced by both CoolAudio and Xvive. There are
> various types available, covering 1024, 2048, and 4096 stage devices.
>
> For flangers, getting the delay short enough is usually the problem. It's
> easy to make a delay of a few msecs, but pushing the clock higher to get
> really short delays and notches that go way up (0.2msec = 2.5KHz, 180
> degrees out of phase, for example) is much harder. 500KHz is good, but only
> just enough.
>
> Tom
>
>
> On 7 Feb 2023, at 18:55, rrsounds via Synth-diy <synth-diy at synth-diy.org>
> wrote:
>
> Generally speaking, BBD devices have a limited number of “buckets." The
> faster you cycle through them, the shorter the delay. 500kHz is going to
> result in a pretty short delay. On the positive side, the S/N is also
> related to cycling rate, resulting in a much cleaner result at higher
> rates.
> Are BBDs even still produced?
> David Reaves
>
> On Feb 7, 2023, at 19:18:08PM, Rutger Vlek via Synth-diy <
> synth-diy at synth-diy.org> wrote:
>
> 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...
>
> Rutger
>
>
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