Could we just use 2 mn3009 in series to obtain 512 stages?

[pietro_moog]

Could we just use 2 mn3009 in series to obtain 512 stages?

[pietro_moog]

nothing special

[lars]

Yes, you can series two MN3009's to achieve 512 stages. It's no different than what EHX did on some of their Memory Man reissues using 4 MN3008's instead of 2 MN3005's.
The real question would be, why not use an MN3004? It has the same active 8 pinout locations (not numbers) as the MN3006, 7 and 9 (you can drop it into a socket for those chips and let the unused 6 pins (5-10) connect to nothing). But the advantage to it's oddball 14-pin configuration makes it less likely to be fake, even off Ebay. It is a virtually unused BBD in the world of guitar effects, but has some great specifications.

[Scruffie]

The answer is it depends on what you're trying to achieve and what compromises you're willing to make but yes you can obtain 512 stages with two in series but getting the right amount of stages is nowhere near the end of the story.

There's an issue with both the MN3004 & TDA1022, insertion loss, that means you're going to need signal makeup gain if you want a 50:50 wet/dry mix which we normally do so that's going to increase noise.

If you're trying to clone a flanger, a lot of them used the chip in parallel multiplex which means to keep the noise levels the same you'd have to use 4 or increase the filtering level.

Every BBD has specific gain vs. clock frequency specs too, if you're trying to build a flanger you want to keep as close to a 50:50 wet/dry mix at all times through its sweep, some of them drop off sooner than others, the 3004 is pretty poor in this regard.

Two BBD's in series does result in poorer performance overall, not such a problem in a delay but perhaps in a lightly filtered chorus those issues might become more obvious. Also you'll really want two bias trimmers to get the best out of them which is another downside.

If you're designing from scratch with specific goals or willing to make changes to an existing circuit to achieve certain benefits at other costs, other BBD's may be better. The MN3009 is great if you want a short delayed chorus or more mild flanger with better high response than an MN3007 so two in series could make a good substitute for an electric mistress where the filtering is extremely light and there's no parallel multiplexing but if you were trying to recreate an original Echo Flanger (disregarding the reissue which was designed to use it) it wouldn't make as much sense as an MN3007.

That's just scratching the surface and some generalisations so the short answer is stages really aren't everything except when trying to achieve longer delay times and you have to know what you're trying to achieve to decide what is the right choice for the circuit.

[pietro_moog]

Thanks