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
Multifaceted response curve from linear CV
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 1 of 1 [10 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
tysseng



Joined: Apr 14, 2013
Posts: 7
Location: Norway

PostPosted: Sun Apr 14, 2013 1:07 pm    Post subject: Multifaceted response curve from linear CV
Subject description: I am having trouble creating a circuit that generates a CV voltage with different components
Reply with quote  Mark this post and the followings unread

Hi!

First of all let me say that I'm an amateur when it comes to analog design, so don't be too hard on me Smile

I am trying to create a circuit that transform a linear CV into a curve with several components. E.g, from 0 to 2V the input should be attenuated by a factor of 2, from 2 to 5 it should be attenuated by a factor of 1.5 or similar. The actual numbers are not important but the principle is.

See my attachments for a drawing of the response I want.

My approach to this is to make two separate amplifier parts. One that generates the first part (from 0 to 2v) and one that generates the second part, and thus is 0v untill the input voltage reaches 2V. I will then sum up the result to get the intended response

The first part is easy. For the second part, my idea is to create a circuit that attenuates the signal by the factor I want, then to add a negative voltage to offset the 0v crossing point so that V-out is 0v when V-in is 2v. Finally I add a diode to reject the negative part so that the response is 0 in the range 0 to 2v. (in my circuit diagram this diode does the oposite, it rejects positive voltages, since I am using an inverting summer).

The circuit I have drawn up works as intended (at fairly low frequencies, but that's ok, the input voltage is controlled using either an LFO or a pot, so high frequencies are not a problem.

What IS a problem however, is that when i try connecting this circuit to an additional summer, or even to a voltage buffer, it does not act very well.

How would I go about connecting this circuit to a summer - or if that is not possible, are there other ways of rejecting the negative/positive part of a signal without using a diode?
--
cheers,
Joakim


JT-response_curve.jpg
 Description:
Wanted response curve, with my suggested approach of adding two separate curves.
 Filesize:  742.25 KB
 Viewed:  40 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

JT-response_curve.jpg



JT-circuit.jpg
 Description:
My attempt at making a circuit that generates the second part of the response curve
 Filesize:  266.27 KB
 Viewed:  38 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

JT-circuit.jpg


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



Joined: Feb 27, 2013
Posts: 161
Location: San Diego

PostPosted: Sun Apr 14, 2013 2:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Your desired response looks like a linear approximation of an exponential. Does it really need to be two linear segments or could you use an exponential converter? Designs for the latter are pretty easy to find.
_________________
My synth build blog: http://gndsynth.blogspot.com/
Back to top
View user's profile Send private message
Scott Stites
Janitor
Janitor


Joined: Dec 23, 2005
Posts: 4121
Location: Mount Hope, KS USA
Audio files: 96

PostPosted: Sun Apr 14, 2013 3:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

This should get you where you want to be:

http://www.oldcrows.net/~patchell/archives/idealdiode.html

_________________
My Site
Back to top
View user's profile Send private message
Scott Stites
Janitor
Janitor


Joined: Dec 23, 2005
Posts: 4121
Location: Mount Hope, KS USA
Audio files: 96

PostPosted: Sun Apr 14, 2013 3:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

For example, I was able to get this response out of a triangle wave (the triangle wave is bottom, the piecewise-linear derivation of the triangle wave is on top).

You can manipulate any CV to go either direction, at whatever gain or attenuation that you want, at any point you want by finagling these building blocks.


piecewise_linear_control.JPG
 Description:
 Filesize:  678.17 KB
 Viewed:  38 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

piecewise_linear_control.JPG



_________________
My Site
Back to top
View user's profile Send private message
elmegil



Joined: Mar 20, 2012
Posts: 1524
Location: Chicago
Audio files: 14

PostPosted: Sun Apr 14, 2013 11:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

You didn't make a batman logo, Scott! Very Happy
Back to top
View user's profile Send private message
Scott Stites
Janitor
Janitor


Joined: Dec 23, 2005
Posts: 4121
Location: Mount Hope, KS USA
Audio files: 96

PostPosted: Mon Apr 15, 2013 5:36 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm Batman!
_________________
My Site
Back to top
View user's profile Send private message
tysseng



Joined: Apr 14, 2013
Posts: 7
Location: Norway

PostPosted: Mon Apr 15, 2013 11:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Wow, thanks for the quick replies, I am stunned Smile Scott: That was exactly what I was looking for. I tried it out, it works perfectly.

gdavis: It looks quite like an exponential function, and I did think about approximating part of it using an exponential function. The real curve goes much further to the right before it suddenly bends upwards. I did read up on antilogarithmic amplifiers using transistors, but was a bit set off by the thermal compensation problem. However, since you called it an exponential converter (I hadn't heard that term before, just antilog or exponential amplifier), I struck gold (for me) right after googling it, with MiK-Music's article https://plus.google.com/107231411209962227230/posts/C8iVtXKzvet Smile

Thanks for all your help. Here is my first try:


P4154770.JPG
 Description:
 Filesize:  2.37 MB
 Viewed:  37 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

P4154770.JPG


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



Joined: Feb 27, 2013
Posts: 161
Location: San Diego

PostPosted: Mon Apr 15, 2013 12:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well I'd never seen the ideal diode circuit before, so I learned something too. That things pretty cool, I spiced it up and it really works great!
_________________
My synth build blog: http://gndsynth.blogspot.com/
Back to top
View user's profile Send private message
Scott Stites
Janitor
Janitor


Joined: Dec 23, 2005
Posts: 4121
Location: Mount Hope, KS USA
Audio files: 96

PostPosted: Mon Apr 15, 2013 12:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

Copyright that waveform ASAP. Then you can sell to AAA as a new, improved logo. Laughing

Bruce Wayne sent me a cease and desist. Crying or Very sad

Laughing

_________________
My Site
Back to top
View user's profile Send private message
corex



Joined: Mar 02, 2010
Posts: 114
Location: Las Vegas

PostPosted: Wed Apr 17, 2013 4:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

This is a very cool circuit... I should try it out. The possibilities are interesting.
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 1 [10 Posts]
View unread posts
View new posts in the last week
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