[sdiy] Shruthi 4PM (was re something else...)

[Roman Sowa]

hi,
I'm not talking about simply shunting the cap with 2 reversed 1n4148, 
but zener diodes, that exhibit their existence in the circuit at higher 
amplitudes, simply preventing from overload, and adding some distortion 
due to softer knee.
I may record some samples of the filter and put them at the website, but 
I assure you it sounds nothing like stomp box.
http://sowa.synth.net/modular/m_vcf.gif

Roman

W dniu 2013-11-30 03:45, Andrew Simper pisze:
> Hi Roman,
>
> What I was getting at is that if you want an ssm2164 to have a
> non-linearity most similar to that of a OTA then the placement of the
> diodes is important:
>
> http://cytomic.com/files/dsp/ssm2164-non-linear-low-pass.png
>
> The input signal is a +- 5 V sawtooth. The blue plots have no
> non-linearity, the red is placing the diode clipper where an OTA has
> the tanh non-linearity, and the purple plots are placing the
> non-linearity to drain the cap and keep its level bounded directly.
> The left plot shows v1 v2 v3 which are the outputs, the right shows v4
> v5 v6 which are the inputs that the 2164. Clipping the high pass
> signal (input - low pass) is good because it preserves the bass of
> your signal while still adding drive. Placing the diode clippers over
> the cap is similar to putting your whole signal through a stomp box
> after it has been low pass filtered.
>
> All the best,
>
> Andy
> --
> cytomic - sound music software
>
>
> On 28 November 2013 16:35, Roman Sowa <modular at go2.pl> wrote:
>> I always do that, by placing diodes across one cap in the filter. Keeps it
>> from overload and adds some character.
>>
>> Anyway, I encourage you to experiment with nonlinear elements here and
>> there. Long time ago I modified Yamaha CS15 with one 1N4148 in the feedback
>> if I recall correctly, and it went crazy. The customer lowed it.
>>
>> Roman
>>
>> W dniu 2013-11-28 03:33, Andrew Simper pisze:
>>
>>> Since everything is so nicely buffered in the 4PM would it be possible
>>> (for those that know the 2164 chip better than me) that if you wanted
>>> more dirt you could insert a pair of diodes at the input of each 2164
>>> to distort the high pass signal that is present there?
>>>
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>