[sdiy] 36dB VCF output drop while increasing emphases

[Harald]

OK guys you all get me wrong. Maybe it's my bad English that i was a bit 
unclear. I don't mean only controlling the feedback loop with an OTA but 
adding gain to the output level of the filter with means of an OTA as 
well. Increasing feedback and increasing output gain at the same time. 
Like it is done in the SuperLadder VCF from OSS (ISS1.1 AUG 1999). 
Sorry, i have no link to the schematic.



Am 19.04.2015 um 11:03 schrieb Olivier Gillet:
> It would be more accurate to say that we got our inspiration from the
> same sources...
>
> Thomas Henry, Osamu Hoshuyama and Roman Sowa had all used the 2164 as
> a 1-pole LPF cell before.
>
> As for the resonance trick, I got it at the source while looking at
> IR3109 filters (it's straight from the Jupiter-8 schematics, 25A OTA :
> http://fa.utfs.org/diy/roland_filters/JP8.jpg). My previous attempt
> was to sum the output of the resonance VCA with the 4th stage, and let
> people customize the soft-clipping they wanted by installing
> back-to-back diodes there.
>
> Actually I use none of the design choices unique to the Dr Octature
> (switchable gain for each stage, 2164 for the feedback VCA). I see two
> benefits in using an OTA over a VCA for the resonance control here :
> differential inputs save you an op-amp, but more importantly the OTA
> non-linearity is what stabilizes the filter and provides the "right"
> flavour of soft-clipping at high-resonance.
>
> On Sun, Apr 19, 2015 at 9:29 AM, David G Dixon <dixon at mail.ubc.ca> wrote:
>>
>>> Am 18.04.2015 um 19:15 schrieb Chris McDowell:
>>>> You might try what Olivier from Mutable did on "Ripples"
>>>>
>>>> http://mutable-instruments.net/static/schematics/Ripples-v01.pdf
>>>>
>>>> The input goes through the same OTA controlling feedback
>>> for resonance.
>>>> Perdy clever!
>>
>> I think he might have learned that from the Dr. Octature, as I do the same
>> thing there, and I believe that Olivier's 4-pole is based on mine.
>>
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>