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 Forum index » DIY Hardware and Software
Adding VC to MFOS WSG filter circuit
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abelovesfun



Joined: Dec 17, 2012
Posts: 18
Location: Portland, OR

PostPosted: Thu Jul 18, 2013 1:21 pm    Post subject: Adding VC to MFOS WSG filter circuit Reply with quote  Mark this post and the followings unread

I wanted to build some simple filter circuits to my modular system, and the 741 MFOS WSG circuit seemed like a good candidate if I could add some CV in.

I've been growing my DIY skills, and recently successfully build some MFOS ADSRs from PCBs, but I still don't know about modifying circuits.

I attached the schematic for the simple filter circuit with my notations pointing out where I think the CV inputs should go. Is this correct? Am I mistaken? Is it even possible?

Thanks so much!


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gdavis



Joined: Feb 27, 2013
Posts: 146
Location: San Diego

PostPosted: Thu Jul 18, 2013 3:12 pm    Post subject: Re: Adding VC to MFOS WSG filter circuit Reply with quote  Mark this post and the followings unread

abelovesfun wrote:
I wanted to build some simple filter circuits to my modular system, and the 741 MFOS WSG circuit seemed like a good candidate if I could add some CV in.

I've been growing my DIY skills, and recently successfully build some MFOS ADSRs from PCBs, but I still don't know about modifying circuits.

I attached the schematic for the simple filter circuit with my notations pointing out where I think the CV inputs should go. Is this correct? Am I mistaken? Is it even possible?

Thanks so much!


Nothing in this circuit is voltage controlled, so no, simply adding CV inputs at those points will not work. All the pots are passing signal feedback so making it voltage controlled is not going to be simple. Vactrols would probably be the easiest way.

I would just look for a VCF.

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diablojoy



Joined: Sep 07, 2008
Posts: 795
Location: melbourne australia
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PostPosted: Thu Jul 18, 2013 3:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

yes it is possible
ray has posted mods on his site for adding CV using JFET's to the WSG
very simple to do. I did it a long time ago using vactrols and also tried rays mods. power starving the circuit is also interesting.

http://www.musicfromouterspace.com/forums.html?CATPARTNO=WSG001&PROJARG=WSG2010%2Fwsg_page9.html&MAINTAB=SYNTHDIY&SONGID=NONE&VPW=1082&VPH=500

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gdavis



Joined: Feb 27, 2013
Posts: 146
Location: San Diego

PostPosted: Thu Jul 18, 2013 3:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Oh, THAT WSG. Sorry, didn't click in my head that it was part of that circuit. The CV mods on that page are for the oscillators though, not the filter. You could probably do something similar to the filter, but as it states on the web site, it's a "pseudo" CV, it wouldn't be very accurate. It will open and close the filter though.
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abelovesfun



Joined: Dec 17, 2012
Posts: 18
Location: Portland, OR

PostPosted: Thu Jul 18, 2013 3:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thank you both! I have three 19" rows of MFOS and one half row of dot.Com running off it's own supply. Since I already "broke format" I thought: "Hey, why not dedicate a row to fun, simple 9V circuits."

I'll likely breadboard the MFOS version with the Mods (thanks so much!!!) against some of these alternates:

Alternate: http://www.muffwiggler.com/forum/topic-35047-0-0.html

Alternate #2: http://electro-music.com/forum/topic-22137.html&postorder=asc&highlight=chaotic+vcf

Alternate #3: http://www.diystompboxes.com/smfforum/forums.html?topic=89022.0;prev_next=next
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gdavis



Joined: Feb 27, 2013
Posts: 146
Location: San Diego

PostPosted: Thu Jul 18, 2013 4:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

There's another discussion of adding CV you might find interesting here:
http://www.electro-music.com/forum/topic-58146.html

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abelovesfun



Joined: Dec 17, 2012
Posts: 18
Location: Portland, OR

PostPosted: Thu Jul 18, 2013 4:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

I really want to thank you both @gdavis and @diablojoy. I really appreciate being able to send off a question and have knowledgeable people like you give it your time and attention. This community is really special, and I'm very thankful to be able to be apart of it.

Keep it coming!
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abelovesfun



Joined: Dec 17, 2012
Posts: 18
Location: Portland, OR

PostPosted: Fri Jul 26, 2013 10:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Is this the proper place to add the quasi-cv modification?


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rossics



Joined: Nov 23, 2013
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PostPosted: Fri Nov 29, 2013 4:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

This is what I did and it worked fine Smile


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