[sdiy] high quality VCA to build?

[Fernando de Izuzquiza]

Hi Steve,

Yes, it helps a lot, thank you.

So, LM13700 and 3080/3280 are good enough for amplitude modulate CV signals (with lin or expo
response) and SSMs and THATs are better for audio-intended VCAs...  Did I get it right?


I saw Mike Irwin's design at EDN. I just wrote him to see if the design can be directly used on a
modular or it needs any adaptation... let's see (I'm not a circuit designer, I can only build... so
I need a bit of help for adapting it)

I also would like to ask to the list if someone built this SSM2164-based VCA and can share the
building tips... it looks like a very fine audio VCA... Anyone?


Thanks again in advance!

Fernando
--



f
*




> De: "Steve Ridley" <spr at spridley.freeserve.co.uk>
> Fecha: Mon, 18 Nov 2002 18:44:39 -0000
> Para: <fdi at ran.es>
> Asunto: Re: [sdiy] high quality VCA to build?
>
>> Do you know of any VCA of very good quality ready to be build?
>> (AC and DC inputs, good dynamic range, etc)
>
> It depends if you want linear or exponential response.  There are
> several good VCA ICs around that offer much better audio
> performance than the CA3280 or LM13700.  Examples are:
>
> THAT 2180 (as used in most professional mixing desks)
> SSM2018
> SSM2164 (quad VCA)
>
> You can get data on these from the THAT and Analog Devices
> websites.
>
> The main problem is that they have exponential control response.  If
> you want an expo response (i.e. dB/volt), they they're wonderful and
> will give you a huge dynamic range and low distortion.
>
> If you want to get a linear response you need to "bend" the CV, which
> makes the VCA significantly more complicated.  Mixing desk manufacturers
> have been doing this for years, often feeding CV through an opamp with
> a diode network in the feedback path.
>
> Someone did a design recently using two section of an SSM2164 per
> VCA.  One section works as an expo VCA and the other section was
> configured as a lin/log converter (reverse of exponential) to turn the
> VCA into a linear one.  The design was published in EDN and was
> discussed a few months ago on SDIY - check the archives.
>
> Does that help?
>
>
>
> Steve Ridley
>
>