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

[Roman Sowa]

Here's the sound of the state variable SSM2164 filter with zeners over 
the cap. I realized after the recording that the example does not show 
the bottom end very much, although there is some of it in the middle.
http://sowa.synth.net/modular/samples/vcf.mp3
1st track of the sequencer controls cut off frequency, 2nd track - 
detune, 3rd track - resonance. Single non-modulated saw oscillator used 
as only audio source, recorded straight from filter output. No edditing 
except cuts from longer recorrding.

Roman

W dniu 2013-12-02 11:00, Tom Bugs pisze:
> Interested in the placing of the zeners -- I'd previously thought you
> could put them over either of the integrating caps - but then I tried
> over the LP caps (had always done over the BP caps) and it didn't work
> (can't remember what happened). I just tried simulating this now (had a
> very similar 2164 VCF already drawn - just with invert on the res chain
> to feed the -ve input of the first opamp) and again the zeners on the LP
> integrator don't seem to work -- simulation seems to go badbad..
> Weird?!
> Ta, Tom
>
> On 02/12/2013 10:46, Roman Sowa wrote:
>> 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?
>>>>>
>>>> _______________________________________________
>>>> Synth-diy mailing list
>>>> Synth-diy at dropmix.xs4all.nl
>>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>
>>
>> -----
>> No virus found in this message.
>> Checked by AVG - www.avg.com
>> Version: 2014.0.4259 / Virus Database: 3629/6883 - Release Date: 12/01/13
>>
>>
>