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 Forum index » DIY Hardware and Software
Escobedo Q&D VCF goes chaotic
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andrewF



Joined: Dec 29, 2006
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PostPosted: Sat Nov 07, 2009 6:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

basically the same, just the two changes i mentioned above. It is worth having the CV input for synth use.
you can still get chaos with the published version - no worries.

some pix here
http://www.sdiy.org/pinky/chaos/chaos.html
and the circuit is still here
http://folkurban.com/Site/QDVCF-714.html
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Uncle Krunkus
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PostPosted: Sun Nov 08, 2009 12:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Those screen shots of the CRO are beautiful. Shocked Very Happy
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andrewF



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PostPosted: Sun Nov 08, 2009 2:37 am    Post subject: Reply with quote  Mark this post and the followings unread

cheers - this is an excellent cct for studying chaos, simple to build and responds very differently to the amplitude, frequency and format (tri, sq, trapezoid, etc) of the input signal.

good aggro filter too..........Tim E. is a genius Very Happy
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frijitz



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PostPosted: Sun Nov 08, 2009 12:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

andrewF wrote:
cheers - this is an excellent cct for studying chaos, simple to build and responds very differently to the amplitude, frequency and format (tri, sq, trapezoid, etc) of the input signal

Shocked Shocked Shocked Shocked Shocked
Amazing work. If I had any idea there was such a rich variety of attractors there I might have worked on it more. Laughing

Those are some of the coolest bottlenecks I ever saw! Do you have a simple explanation as to why you get three scrolls out of the system? I never would have expected that.

Very Happy

Ian
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andrewF



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PostPosted: Sun Nov 08, 2009 4:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Laughing bottlenecks! Thanks Ian - I was actually spending all my time trying to get an image like the one you posted on pg 1 of this thread, that one is quite stunning.

To get these the input is a low frequency trapezoid around 20-30Hz (Don Tillman's VCO). They are great to watch, the 3rd bottleneck is quite unstable as you can see it looks quite scratchy. It gets spat out, wobbles around for a few seconds and is gone.

I'm getting pressured to work out the maths for this circuit, not exactly my favorite job, but will post it here when (and if) it happens.
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frequencycentral



Joined: May 25, 2008
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PostPosted: Sun Nov 08, 2009 8:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

Folk Urban: http://folkurban.com/Site/GuitarEffects-681.html
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thepaddiscuile



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PostPosted: Fri Jul 23, 2010 10:46 am    Post subject:   Reply with quote  Mark this post and the followings unread

Hi guys.. Anyone know how you.d get a highpass response from this..

Be cool to have both running in series lp-hp
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andrewF



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PostPosted: Sat Jul 24, 2010 8:51 am    Post subject: Reply with quote  Mark this post and the followings unread

In a sense it already has the hi-pass.
In a regular twin-t filter, the two sections deliver a low-pass and a hi-pass function, combined the result is a notch filter.

Of course the added diode means the Q&D is not normal.

From http://en.wikipedia.org/wiki/RC_oscillator

The second common design is called a "Twin-T" oscillator as it uses two "T" RC circuits operated in parallel. One circuit is an R-C-R "T" which acts as a low-pass filter. The second circuit is a C-R-C "T" which operates as a high-pass filter. Together, these circuits form a bridge which is tuned at the desired frequency of oscillation. The signal in the C-R-C branch of the Twin-T filter is advanced, in the R-C-R - delayed, so they may cancel one another for frequency f=\frac{1}{2\pi RC} if x = 2; if it is connected as a negative feedback to an amplifier, and x>2, the amplified becomes an oscillator.

Hope this doesn't put you off, I'm quite interested in the Q&D and would love to learn any new tricks with it. On my breadboard at the moment I have a version with the op-amp replaced by a 4009 inverter, it filters but no chaos yet.
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kurodama



Joined: Jul 23, 2010
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PostPosted: Sat Jul 13, 2013 5:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Sorry to revive this old thread, but this filter design kind of struck me and I tried to build it on breadboard. I admit that I'm not the most experienced synth maker, in fact I'm a total noob. I currently try to understand how OpAmps work and this seemed like a nice project to try some things out.

I've built the original version from the gif file, and so far the filter seems to work, the audio gets through and the pots do change the signal. Also I can modulate it using an LFO from the modular.

The only thing is that it does really not sound like a filter, more like a distortion. I guess it's supposed to sound like that, it's the "chaos" part isn't it?
I can't tell from the mp3 that has been posted at the beginning if my circuit is sounding similar or not...

The Vr thing confused me too btw. What I did was to connect the 1M resistor right after the IN to ground. Also I've connected the V- on the OpAmp to ground. Is this how it is supposed to be?

I'm currently running this off a 9v battery, but I'm thinking about making it on perfboard to be used in my eurorack modular... so I could also adapt it to +/-12v... just not sure how I should do that...

Well, if anybody has some tips for me on this, it would be really appreciated! thanks!

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kurodama



Joined: Jul 23, 2010
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Location: Italy

PostPosted: Mon Jul 15, 2013 12:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've made some recordings of how this filter sounds in my breadboarded version. You can find them here:
http://papernoize.tumblr.com/post/55448137952
One thing I noticed is that, despite this being a lowpass filter it does not really attenuate the high frequencies that much...

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elmegil



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PostPosted: Mon Jul 15, 2013 6:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

The PDF has no CV in....
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kurodama



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PostPosted: Tue Jul 16, 2013 1:07 am    Post subject: Reply with quote  Mark this post and the followings unread

no but if you check Andrew's post, he mentions where to add it. Or you can just compare the two schematics...
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elmegil



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PostPosted: Tue Jul 16, 2013 6:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Someone else was asking what was the difference between a couple versions posted, but those posts appear to be gone now? That'll show me for not quoting Smile
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