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[Emmanuel AMADIO]

>I have a JX10 I want to mod.
>The filter is a State Variable filter according to the Roland Service 
>Manual.
>but it seems it is usable only in lp mode (not a problem).
>the filter seems to be set as a 2 poles filter whereas in the JX8P wich use 
>the same VCF chip it seems to be a 3 poles
>filter.

The thing which I can't understand is why the circuit has different capacitors values.
Does it mean that they gave the filter response a slope like this ? :


--------- 
         ^^^^^
              ^^^^^
                   \
                    \


> The block diagram for the chip is like this :
>             --------- 
> fc  ------->|       |---------------------------
>             |       |           |              |
> res ------->|       |-----------|------------- |
>             ---------         | |            | |         
>                               | |            | |         
>                             -------        -------
>                             |     |        |     |
> in ------------------------>| vcf |------->| vcf |----> out
>                             |     |        |     |
>                             -------        -------
>                              |   |          |   |
>                              -   -          -   -
>                           C1 -   - C2    C3 -   - C4
>                              |   |          |   | 
>                ---------------------------------------- GND
>                       
> C1=C2=10 nF 
> C3=C4=220 pF

The other strange thing is that for the JX8P  C1=C2=C3=10 nF and C4=220pF

Regards Emmanuel