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

[Tom Bugs]

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
>
>

-- 
BugBrand LTD
UK company No. 07199808
VAT No. GB 988 2629 57
1 Ninetree Hill
BRISTOL BS1 3SB
United Kingdom
www.bugbrand.co.uk