electro-music.com   Dedicated to experimental electro-acoustic
and electronic music
 
    Front Page  |  Articles  |  Radio
 |  Media  |  Forum  |  Wiki  |  Links  |  Store
Forum with support of Syndicator RSS
 FAQFAQ   CalendarCalendar   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   LinksLinks
 RegisterRegister   ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in  Chat RoomChat Room 
 Forum index » DIY Hardware and Software
Escobedo Q&D VCF goes chaotic
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 1 of 2 [38 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Goto page: 1, 2 Next
Author Message
frijitz



Joined: May 04, 2007
Posts: 1710
Location: NM USA
Audio files: 54

PostPosted: Thu Nov 29, 2007 9:12 pm    Post subject:  Escobedo Q&D VCF goes chaotic
Subject description: Can your VCF do this?
Reply with quote  Mark this post and the followings unread

Yes folks, it's real. If Tim Escobedo's Q&D VCF:
http://www.geocities.com/tpe123/folkurban/fuzz/simplevcf.gif
is overdriven a bit it goes chaotic.

The circuit I used is almost the same as Tim's, except that it is run from a 12 V supply. With low Q (10 k on the resonance pot) and 0.6 V peak drive (from a TRI VCO) a sweep of the drive frequency produces a series of period doublings followed by a chaotic region (even with the usual small windows of periodicity!) followed by a final period undoubling. The attached file is a recorded sweep.

I've checked quite carefully that this is real and not just an artifact. The chaotic pattern depends on the type of diode used and goes away if the diode is substituted by a resistor. In the latter case, the filter looks like a bandpass filter driven into clipping, as expected.

Analyzing the circuit and simulating its response would be a fairly tedious job. But the necessary conditions for chaos are there: the system is of third order (with the drive included) and the diode provides the necessary nonlinearity.

This encourages an idea I've had for some time: to make a combo module that will operate as either a filter or a chaos generator. This now looks within reach.

Many thanks to Graham Meridith for pointing out this circuit, to Tim for a patient discussion of the filter's operation and to Scott Stites for pointing out that the MS20 filter has some unusual multiphonics when overdriven.

Very Happy

Ian


filt_ch02.mp3
 Description:

Download
 Filename:  filt_ch02.mp3
 Filesize:  379.31 KB
 Downloaded:  983 Time(s)

Back to top
View user's profile Send private message
loss1234



Joined: Jul 24, 2007
Posts: 1535
Location: nyc
Audio files: 41

PostPosted: Thu Nov 29, 2007 9:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

so you did nothing to the circuit except change to a 12v supply?

I have been interested in non-linearity for a long time and I see that you have mentioned many times that diodes have non-linear properties. So is it possibe to add chaotic elements to circuits by replacing resistors with diodes? Or do you really need to approach this from a math standpoint?

I ask because I am wondering if there are ways to take MORE pre-existing circuits and push them toward chaos.


thanks for all your work into chaos circuits. I only hope my skills catch up to my interest in this field.

_________________
-------------------------------------------- check out various dan music at: http://www.myspace.com/lossnyc
http://www.myspace.com/snazelle
http://www.soundclick.com/lossnyc.htm http://www.indie911.com/dan-snazelle
Back to top
View user's profile Send private message
Tim Escobedo



Joined: Nov 27, 2007
Posts: 3
Location: California

PostPosted: Thu Nov 29, 2007 9:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Wow. That's a pretty neat bug/feature. I can't even begin to account for that behavior. If only I knew about it earlier. Smile

I'm curious. What kind of op amps are you using? I almost universally use plain low powered TL06x chips. Occasionally TL07x series. I noticed the SK quad filters were 5534 I think. I have in the past treated op amps rather generically.
Back to top
View user's profile Send private message
frijitz



Joined: May 04, 2007
Posts: 1710
Location: NM USA
Audio files: 54

PostPosted: Fri Nov 30, 2007 8:42 am    Post subject: Reply with quote  Mark this post and the followings unread

loss1234 wrote:
so you did nothing to the circuit except change to a 12v supply?

So is it possibe to add chaotic elements to circuits by replacing resistors with diodes? Or do you really need to approach this from a math standpoint?


No significant changes. The feedback network is the same, except for 450p instead of 500p for the small cap. (A larger cap actually gives a more dramatic chaotic behavior.) The CV input is not connected. The freq control has a bypass cap, but it doesn't make any difference. The bypass cap at the Vcc/2 supply is left off, but that doesn't make any difference either. The audio coupling cap is 0.1 instead of 0.01.

In general, chaos only occurs under special conditions, so just throwing some nonlinear element into a circuit usually doesn't result in anything interesting. That's why I was so surprised to see chaos in this circuit. Most of the work I have done with chaos is based on systems that have been studied previously.

Very Happy

Ian
Back to top
View user's profile Send private message
frijitz



Joined: May 04, 2007
Posts: 1710
Location: NM USA
Audio files: 54

PostPosted: Fri Nov 30, 2007 8:53 am    Post subject: Reply with quote  Mark this post and the followings unread

Tim Escobedo wrote:
Wow. That's a pretty neat bug/feature. I can't even begin to account for that behavior. If only I knew about it earlier. Smile

I'm curious. What kind of op amps are you using? I almost universally use plain low powered TL06x chips. Occasionally TL07x series. I noticed the SK quad filters were 5534 I think. I have in the past treated op amps rather generically.


Yeah, i didn't expect the chaos at all. At first I thought I was just having trouble with my scope triggering. But triggering off the input signal straightened me out on that.

I used an LF351 (similar to TL071). I also threw in an older slow opamp (BB3500, similar to LM307), but other than the slower slew rate it worked the same. So I don't think there is any major contribution from an opamp pole or anything weird like that.

The signal is different from anything I have seen before. As the input signal crosses zero from below, the opamp slews very rapidly upward, usually clipping. Then the decay of the waveform is much slower. So the opamp clippping may be an important part of the systems nonlinearity. Not sure about that at this point.

Very Happy

Ian
Back to top
View user's profile Send private message
frijitz



Joined: May 04, 2007
Posts: 1710
Location: NM USA
Audio files: 54

PostPosted: Fri Nov 30, 2007 7:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've looked at this interesting circcuit a bit more. After reducing the input drive to +/-50 mV there is still nonlinear behavior. As the driving frequency is increased there is a resonance when f = f0 (the main resonant frequency) then around f = 2f0 the period of the output signal doubles and there is another resonance at f = 2f0. So the resonance occurs twice at the same output frequency but for input frequencies of f0 and 2f0. I'm surprised nobody has noticed this before. I have checked all the wiring and the component values very carefully. Well, perhaps it's the larger supply voltage.

Ian
Back to top
View user's profile Send private message
frijitz



Joined: May 04, 2007
Posts: 1710
Location: NM USA
Audio files: 54

PostPosted: Sat Dec 01, 2007 2:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

A little further work on this interesting circuit. I tried it powered by a 9V battery and I seems to behave about the same as with 12V. Adding a small resistor in series with the diode reduces the tendency to chaos and rounds off the waveform a bit. A scope shot of the attractor seen with a 1 k series resistor is attached. The two signals used were the output and the voltage at the top of the diode. It's a very interesting shape. I can't recall seing an attractor quite like this before, although I can't quite follow how it is folded.

Very Happy

Ian


filtch01.jpg
 Description:
 Filesize:  22.02 KB
 Viewed:  12391 Time(s)

filtch01.jpg


Back to top
View user's profile Send private message
loss1234



Joined: Jul 24, 2007
Posts: 1535
Location: nyc
Audio files: 41

PostPosted: Sat Dec 01, 2007 4:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

wow.

i need a scope!

ordered those parts for the chaos circuits today.

hopefully next week i can start learning more about this.

thanks as usual for the great info

_________________
-------------------------------------------- check out various dan music at: http://www.myspace.com/lossnyc
http://www.myspace.com/snazelle
http://www.soundclick.com/lossnyc.htm http://www.indie911.com/dan-snazelle
Back to top
View user's profile Send private message
StephenGiles



Joined: Apr 17, 2006
Posts: 481
Location: England

PostPosted: Sat Dec 01, 2007 4:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

Our dog was quite alarmed at the noise!
Back to top
View user's profile Send private message
gmeredith



Joined: Jun 28, 2006
Posts: 82
Location: Tasmania, Australia
Audio files: 1

PostPosted: Sun Dec 02, 2007 9:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Frijitz,

You seem to really be developing something here! If you can figure out just what makes the chaos, it would make a great bend for the Casio SK Phat Philter he he Very Happy

Did you build the filter straight from Tim's schematics, or from my Phat Philter plans? I'm trying to find out what the difference must be. What op-amp are you using?

I did come across an anomality while designing the board. I found that a TL071 op-amp has a dead zone when you turn the cutoff 100K pot below, say, 1 quarter. it just seemed to mute. Other op-amps didn't show this behaviour.

I had the input attenuated a fair bit for line level input, so I didn't have it overloaded to see what it would have done otherwise. Interesting.

Cheers, Graham
Back to top
View user's profile Send private message
frijitz



Joined: May 04, 2007
Posts: 1710
Location: NM USA
Audio files: 54

PostPosted: Sun Dec 02, 2007 10:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Graham -- As discussed some above, I have looked at a number of variations of the circuit, including different opamps and supply voltages. I RE'ed your layout, and it seems to me basically the same circuit as the original. There is no chaotic behavior when the diode is replaced by a resistor. So the diode is actually doing two things, I believe: (1) it acts as a tunable resistance in the twin-T network (as intended) and (2) it acts as a nonlinear circuit element, thereby inducing the chaotic behavior. It would take some fairly tedious numerical analysis to show that the chaos is expected, but it really doesn't seem all that improbable (in hindsight!). If you have the means, you might try driving it a bit harder to see what happens in your setup.

Very Happy

Ian
Back to top
View user's profile Send private message
loss1234



Joined: Jul 24, 2007
Posts: 1535
Location: nyc
Audio files: 41

PostPosted: Thu May 08, 2008 10:23 am    Post subject: Reply with quote  Mark this post and the followings unread

ian

i have been building this circuit and I wanted to know if you bothered using the VR bias (when you used a 12v supply)

in other words, on tims original schematic he shows a SINGLE supply being split in half and then fed into the 1m vr resistor going into the +input. did you emulate this with 12v or just skip it and use bipolar?

one thing i noticed (and most likely why tim included the trimmer) is that the circuit distorts very easily, and not in a very pretty way either. is this the key? just overdriving that input? i can tell already that this has a much stranger response than my other filters.

thanks

(scope is coming this week!)

_________________
-------------------------------------------- check out various dan music at: http://www.myspace.com/lossnyc
http://www.myspace.com/snazelle
http://www.soundclick.com/lossnyc.htm http://www.indie911.com/dan-snazelle
Back to top
View user's profile Send private message
frijitz



Joined: May 04, 2007
Posts: 1710
Location: NM USA
Audio files: 54

PostPosted: Thu May 08, 2008 12:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

loss1234 wrote:
i have been building this circuit and I wanted to know if you bothered using the VR bias (when you used a 12v supply)
in other words, on tims original schematic he shows a SINGLE supply being split in half and then fed into the 1m vr resistor going into the +input. did you emulate this with 12v or just skip it and use bipolar?


Both. I used 0/12V (and 0/9V) with the split, and I used +/-12V without it.

I dropped working on this, as the Threeler was much more interesting.

Very Happy

Ian
Back to top
View user's profile Send private message
loss1234



Joined: Jul 24, 2007
Posts: 1535
Location: nyc
Audio files: 41

PostPosted: Thu May 08, 2008 6:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

well then i must buy the threeler pcb!!

BUT i am working with this for a 9v battery powered circuit

_________________
-------------------------------------------- check out various dan music at: http://www.myspace.com/lossnyc
http://www.myspace.com/snazelle
http://www.soundclick.com/lossnyc.htm http://www.indie911.com/dan-snazelle
Back to top
View user's profile Send private message
Mikmo



Joined: Dec 01, 2005
Posts: 150
Location: Copenhagen - Denmark

PostPosted: Thu Sep 04, 2008 12:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry to revive an old thread, but did anybody design a PCB for this filter?

If so i would really like to see / buy it.

Thanks

Mikael

_________________
Stay Cool
Mikael
http://www.mikmo.dk
Back to top
View user's profile Send private message Visit poster's website
fonik



Joined: Jun 07, 2006
Posts: 3759
Location: Germany
Audio files: 23

PostPosted: Fri Sep 12, 2008 5:37 am    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
Both. I used 0/12V (and 0/9V) with the split, and I used +/-12V without it

i have to confess: i don't get it from the schematic Shocked

if i use the split i get a virtual ground labeled Vx, right? where does this apply to the circuit? what does Vr mean? why is the attenuator wired to the ground symbol when i split the supply?

i would have expected the following:
using the split, the attenuating pots are wired to virtual ground Vx. same applies to the 1M resistors at the positive OpAmp inputs. freq control potentiometer goes from +V to ground (actual the virtual -V)...

maybe i am a little bit dumb, but i don't understand the schematic here, so any explanation is appreciated.

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Uncle Krunkus
Moderator


Joined: Jul 11, 2005
Posts: 4759
Location: Sydney, Australia
Audio files: 52
G2 patch files: 1

PostPosted: Fri Sep 12, 2008 5:47 am    Post subject: Reply with quote  Mark this post and the followings unread

Where is the schem?
_________________
What makes a space ours, is what we put there, and what we do there.
Back to top
View user's profile Send private message Visit poster's website
jnuaury



Joined: Feb 28, 2008
Posts: 162
Location: chicago
Audio files: 9

PostPosted: Fri Sep 12, 2008 7:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Uncle Krunkus wrote:
Where is the schem?


http://www.geocities.com/tpe123/folkurban/fuzz/simplevcf.gif
Back to top
View user's profile Send private message AIM Address
frijitz



Joined: May 04, 2007
Posts: 1710
Location: NM USA
Audio files: 54

PostPosted: Fri Sep 12, 2008 7:36 am    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
frijitz wrote:
Both. I used 0/12V (and 0/9V) with the split, and I used +/-12V without it

i have to confess: i don't get it from the schematic Shocked
if i use the split i get a virtual ground labeled Vx, right? where does this apply to the circuit? what does Vr mean?

I don't see any Vx on the schematic. It's an odd circuit, but it goes chaotic under a variety of conditions.

Very Happy

Ian
Back to top
View user's profile Send private message
fonik



Joined: Jun 07, 2006
Posts: 3759
Location: Germany
Audio files: 23

PostPosted: Fri Sep 12, 2008 11:33 am    Post subject: Reply with quote  Mark this post and the followings unread

right. i misread the Vr in the split circuit for Vx, due the serife font Rolling Eyes

however, i would have expected the attenuating potentiometer on the audio input to go to Vr then. isn't Vr the virtual ground here?

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
frijitz



Joined: May 04, 2007
Posts: 1710
Location: NM USA
Audio files: 54

PostPosted: Fri Sep 12, 2008 1:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
however, i would have expected the attenuating potentiometer on the audio input to go to Vr then. isn't Vr the virtual ground here?

Right. That's just how Tim's circuit is. The circuits I did with unipolar and bipolar supplies were not equivalent to each other. But both showed chaos. Whiteboard it up and try it!

Very Happy

Ian
Back to top
View user's profile Send private message
fonik



Joined: Jun 07, 2006
Posts: 3759
Location: Germany
Audio files: 23

PostPosted: Fri Sep 12, 2008 4:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
fonik wrote:
however, i would have expected the attenuating potentiometer on the audio input to go to Vr then. isn't Vr the virtual ground here?

Right. That's just how Tim's circuit is. The circuits I did with unipolar and bipolar supplies were not equivalent to each other. But both showed chaos. Whiteboard it up and try it!

Very Happy

Ian

thank you ian. i will do that. again you gave me some good answers today (as always) - thank you very much.

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
alcofribas



Joined: Oct 03, 2008
Posts: 20
Location: Eastern France

PostPosted: Sat Nov 07, 2009 5:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Geocities has been dead for a while now, can somebody post that mysterious schematic again?

Thnx

Alcofribas
Back to top
View user's profile Send private message
andrewF



Joined: Dec 29, 2006
Posts: 1174
Location: australia
Audio files: 4

PostPosted: Sat Nov 07, 2009 9:15 am    Post subject: Reply with quote  Mark this post and the followings unread

this is a version I used for getting chaotic signals
pretty sure the only change is the CV input was removed and R9 (1k) was added (Ian Fritz's suggestion).
To add a CV input just connect it via a 100k resistor to the junction of D1 and R2. You can leave in R9 if you like.
Doesn't matter what op-amp, any will do.


q&dschemo.pdf
 Description:

Download
 Filename:  q&dschemo.pdf
 Filesize:  40.59 KB
 Downloaded:  506 Time(s)

Back to top
View user's profile Send private message Visit poster's website
crochambeau



Joined: May 18, 2008
Posts: 31
Location: earth.

PostPosted: Sat Nov 07, 2009 11:40 am    Post subject: Reply with quote  Mark this post and the followings unread

I too am interested in the chaotic version, the attached files does not come through... (edit, as soon as I open my mouth I'm proven wrong..)

How's it different from the schematic culled from archived geocities?

http://web.archive.org/web/20060402010333/http://www.geocities.com/tpe123/folkurban/fuzz/simplevcf.gif

_________________
http://crochambeau.blogspot.com/
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 1 of 2 [38 Posts]
View unread posts
View new posts in the last week
Goto page: 1, 2 Next
Mark the topic unread :: View previous topic :: View next topic
 Forum index » DIY Hardware and Software
Jump to:  

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
e-m mkii

Please support our site. If you click through and buy from
our affiliate partners, we earn a small commission.


Forum with support of Syndicator RSS
Powered by phpBB © 2001, 2005 phpBB Group
Copyright © 2003 through 2009 by electro-music.com - Conditions Of Use