[sdiy] High frequency VCO as BBD clock

[Tom Wiltshire]

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 <mailto: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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