[sdiy] THAT 2181C VCA's

[Stephen Lenham]

THAT VCAs are superb devices. They are aimed squarely at very high 
performance audio and as far as fidelity is concerned they are in a 
completely different league to SSM2164s, CA3280s, etc.

I've worked with them many times in pro audio/broadcast designs and 
have been very happy with them. The only thing that ever baffled me was 
why they don't (yet) produce a matched stereo device.

There is no reason they couldn't be used in place of any other log VCA, 
although their very lack of colouration might be seen as a drawback in 
synths, where 'character' is important.

Re linearising them, check out the THAT2252. It's intended as an rms 
audio level detector, but can be used as a simple log converter and 
when connected to a THAT VCA their tempcos cancel to give zero 
temperature drift. They also do the two in the same package (THAT4301), 
but they're not the cheapest devices ever.

I always thought it should be possible to build a temperature 
compensated VCO with just one of these (a la CEM3340) but can't quite 
do it...this may be helped by a new device THAT have launched which 
includes a Proportional To Absolute Temp output (as found on the 3340). 


Oh yes - I'm not paid by THAT Corp. either (though if they offered...)

Cheers,

Steve L.



> Hello,
>  Wondering if anyone here has worked with the THAT
> 2181 VCA's. I have 200+ of these and would like to use
> a couple of them for VCF's and VCO's as well as VCA's.
> Any idea's, suggestions...?
> 
>  Thanks,
>   steve
> 
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