[sdiy] Multiplier vs VCA?

[marc bareille]

Hello ,

>I think there are 2 main reasons.
>1) Availablity and cost. Having to order a tube of something at $4-$5 a pop from the manufacture.
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well cost of THAT  ( ex-DBX) VCAs is certainly proportionnal to their 
sound qualities: they are excellents !!!
far away from all OTAs and other VCA i know ... There is also the THAT 
2002  composed of eigth  2180 in parallel if you want to reach the top 
of  the  hi-end ! they are a  bit too much luxuous for synthesis 
anyway,  but for a mastering compressor , it is the right part to use ;)

>2) If I remember right these have a log response to control voltages.
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Exact .

>a) Most of our VCAs have linear responses because our envelope generators have a log curve.
>  
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it is not really a problem   i use them with a exp/lin  envelopes  
without any troubles ...

>b) Have to get really creative to use these in VCOs with a exponental freq response.
>  
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Never tried this ...

>c) Only place I can think of a log device being useful is for a pan/morph circuit.
>
>  
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I do not agree at all  there are so many place where those chips can be 
useful !!!..They are massively  present  in large mixing desk (old  SSL 
consoles  are full of them ) as VCAs , compressors , expanders , noise 
gates, Cv mixers,parametric filters ..etc ... In fact  all kind of 
analog dynamic processors ...

Also check my  dual VCA module builded with the old version of the 218x  
: the dbx2150 ... You can replace the 2150 almost directly by a 2180 in 
this schematics ..( It is  at http://m..bareille.free.fr   chapter 
"synths modules"  ) They are  output audio VCAs  of my modular synth  
and i wouldn't replace them by anything else ! 

One tip for those who would like to try them : i hardly advise to use 
the symetrical wiring of the CV control line because the VCA chip  can 
generate audible pops/tumbs whit fast CV variation from min to max ... 
this kind of wiring help to eliminate  this small side effect  very well . 

Best Regards,

Marc B.


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