New Stuff

[mbartkow at ET.PUT.Poznan.PL]

> This is a very nice VCA indeed, and worth to be added to any modular system.
> I've built it twice, meanwhile, for my Minimoog clone and - a slightly
> expoanded version - for my JH-4. 
> Opamp-less VCAs, designed for soft limiting rather than hard clipping,
> can really make a difference.

Please help me, I don't get it. 

First of all, what is the reason to use as many as three differential stages ?

BTW, I cannot see how the middle stage works in the absence of external
loudness cv. I think, if Ib of Q6 is zero, the Q4+Q5 should realise a
very high attenuation. Should probably the base of Q6 be grounded through
the 33K ?

I am also very curious, why all the resistances are so small. The 1K,
470R and 8R2 (?!!) inside the differential pairs are a little bit mysterious,
too. My guess is that all these are designed to obtain that special soft
saturation behaviour mentioned by Juergen, but I do not have enough knowledge
about differential transistor pairs to explain it.

Would some transistor guru please provide some explanation/analysis ?

thanks,

MB


--

Maciej Bartkowiak, PhD
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