[sdiy] Roland System 700 VCF

[Stewart Pye]

Hi Aaron,

Yes, that is pretty close. I was going on the misunderstanding that the 
SSM2164 was designed with an inverted current output so that the output 
was non inverted when going through an inverting op amp. David Dixon 
straightened me out on this, and I realised the circuit is quite simple 
as the schematic you linked to shows.

When I get some 2164's I'll breadboard it, probably with a soft clipping 
stage in the feedback path, but not an OTA for voltage control.


Regards,
Stewart.

lanterma at ece.gatech.edu wrote:
> On Jul 10, 2010, at 4:51 PM, Stewart Pye wrote:
>
>   
>> Since the input of each stage is going into the non inverting input of the OTA and the OTA then goes to an inverting integrator, it is negative feedback through the 22K resistor. However I believe that when using the SSM 2164 followed by an inverting stage, the output is not inverted. If this is true I'd have to either add an inverting op amp stage for the feedback, or add a differential amp in front of the VCA.
>>     
>
> Here's something pretty close to what you're aiming at: 
>
> http://userdisk.webry.biglobe.ne.jp/000/024/65/1/VcfSSM0602a.GIF
>
> - Aaron
>
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