[sdiy] BBD's in series and accumulative S/N ratio degradation.

[Tom Wiltshire]

Personally, I would recommend using one longer delay chip over using three short ones in series.

The reason why is that you're supposed to filter the signal between stages to remove clock noise. The clock noise will (in theory) cause aliasing in the next BBD and so should be filtered. All those filters add a lot of extra circuitry for just a few stages of delay.

I've done this using 4 x MN3005 4096-stage BBDs in a (desperate) attempt to get a longer analog delay. In that situation, you really do need the inter-stage filtering to keep noise under control, but you're fighting a losing battle at that point. Oh, and you probably need to wrap a 570/571 compander around it just so you don't get lost in the waterfall!

In your situation, I'd use a 1024-stage BBD and clock it faster. You'll get much better S/N and wider bandwidth, with less circuitry. Save the little BBDs for super-short delays for flangers and such like.

HTH,
Tom

 
On 23 Dec 2011, at 04:20, aankrom wrote:

> I have several MN3006's that I thought of using, but to get longer delay times, I plan to use two or three in series. Am I right in thinking that the S/N ratio would be the same as that of a comparable single BBD's S/N ratio? That is you don't just add up what appears to be accumulative S/N ratio loss based on the rated S/N ratio of the device since it's in dB's. Like if two people are talking to you at a level of 60 dB's each, the sound level isn't 120 dB's, but rather 63 dB's. I know that under-clocking the MN3006 would make the S/N ratio sucky for sure... Not to mention limiting the bandwidth...
> 
> AA
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