[sdiy] SSM2164 Questions

[Neil Johnson]

Hi Stewart,

Stewart Pye wrote:
> The Electrical Characteristics don't tell any more than this:
> ground referenced –33 mV/dB control port
>
> and the single supply example states: 0dB gain at Vc = V+/2.
>
> This leads me to believe the following when using a +/-15V supply...
> 1. There is 0dB of gain when the control port is at 0V.
> 2. Gain increases 1dB for every 33mV more negative the control  
> voltage is (eg -99mV would be +3dB gain)
> 3. Gain decreases 1dB for every 33mV more positive the control  
> voltage is.
> 4. The maximum attenuation is quoted as -100dB, so to get this  
> you'd need 100 * 33mV = +3.3V
> 5. The maximum gain is quoted as +20db, so to get this you'd need  
> 20 * 33mV = -0.66V
> 6. In normal synthesizer use such as a VCF you'd use an inverting  
> summing stage for your CV inputs and add an offset so that with a  
> 0V CV input you'd get maximum attenuation (somewhere around +3.3V),  
> and gain would increase with increasing CV input voltage.
>
> For those that have played with these chips do these seem like  
> reasonable conclusions?

Yeah, that's a good start.   Some practical examples with the 2164  
can be found here:

http://www.milton.arachsys.com/nj71/index.php? 
menu=2&submenu=0&subsubmenu=0

The exact relationship between external CV and voltage applied to the  
2164 control port depends on the type of function.  For example, in  
the VCF the frequency response needs an inverter as you say, while  
the resonance needs a non-inverting buffer to give the correct  
control law (increasing CV gives increasing Q).

Cheers,
Neil
--
http://www.njohnson.co.uk