[sdiy] SSM2164 panning curve

[Tom Wiltshire]

Derek,

I'm afraid I don't understand what you're trying to do. I need to see  
more diagrams for my visual head to get it. So long as you're clear  
about it, that doesn't matter.

However, I have played with the SSM2164. 15V is too much for the  
control port. The datasheet gives the CV response as -33mV/dB.
Hence you need 3.3V for fully off -100dB, and -0.66V for 20dB gain,  
with 0V giving you unity gain. I don't know of a way to set the  
SSM2164 up for attenuation only. You just make sure that you only  
have positive control signals. I don't think just a simple diode  
would work that well, since the diode won't conduct until the CV is  
significantly negative, which isn't what you want. You could modify  
the op-amps in the Electro-music schematic to precision half-wave  
rectifiers, which would give you a more accurate result.

Regards,
Tom


On 23 Jul 2009, at 11:31, Derek Holzer wrote:

> I've got a hopefully simple question about using the SSM2164 as a  
> joystick controlled quadraphonic spatializer/panner. I have been  
> looking at Marc Bareille's Quad VCA/CV-Mixer as a good model for  
> this project:
>
> http://m.bareille.free.fr/modular1/quadvca/quadvca.htm
>
> with some additions for the joystick control:
>
> http://electro-music.com/forum/viewtopic.php?t=24705
>
> My concern is this: when the joystick is it dead center the gain on  
> all channels should be unity. However, for this particular gain/ 
> panning curve I don't want more than unity gain, only attenuation.  
> I am aware that this nulls the effects of half the range of the  
> joystick... however from what I have read this is the panning curve  
> used by the Serge and Buchla spatializers, and it makes sense  
> acoustically to me.
>
> So let's assume that set up the SSM2164 as in the datasheet, where  
> 0V is unity and minus voltage is attentuation. And I wire up my  
> joysticks as voltage dividers between +15 and -15 (or should it be  
> +/-5V?). But since I don't want any amplification, I use a diode to  
> block the positive voltage coming from the joysticks, making sure  
> the diode is rated not to break down anywhere near 15V (or 5V?). Am  
> I on the right track? Or is there a way to set up the SSM2164  
> itself so that it only attenuates?
>
> Thx+best!
> Derek
> -- 
> ::: derek holzer ::: http://blog.myspace.com/macumbista ::: http:// 
> www.vimeo.com/macumbista :::
> ---Oblique Strategy # 52:
> "Do nothing for as long as possible"
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