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 Forum index » DIY Hardware and Software » Thomas Henry designs
Voltage Controlled Crossfader/VCA
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Thomas_Henry



Joined: Jul 24, 2009
Posts: 144
Location: N. Mankato, MN

PostPosted: Mon Aug 06, 2012 7:57 pm    Post subject: Voltage Controlled Crossfader/VCA
Subject description: Another circuit for your consideration
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Hi Gang,

As promised, here is another circuit for you to play with. It can be used either as a voltage controlled crossfader or as an ordinary VCA. I hit upon this when finally realizing something that was in front of me all the time---the control currents though the voltage-to-current converter are symmetric yet opposite. It's an obvious idea once you see it and has probably been used before. But I was glad to stumble upon it.

Null out the DC thumps in the usual way. (Turn the audio inputs down, then apply a 0 to +5V square wave to the CV input.)

The usual legalese applies. Feel free to use this for personal applications but don't copy, or produce commercially. Anyone wanting to do a non-commercial PCB for EM users please contact me first.

Have fun!

Thomas Henry


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v-un-v
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Joined: May 16, 2005
Posts: 8934
Location: Birmingham, England, UK
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PostPosted: Tue Aug 07, 2012 3:14 am    Post subject: Reply with quote  Mark this post and the followings unread

Looks fun Mr Henry! Cheers! Very Happy
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inlifeindeath



Joined: Apr 02, 2010
Posts: 315
Location: Albuquerque, NM

PostPosted: Wed Aug 08, 2012 10:17 am    Post subject: Reply with quote  Mark this post and the followings unread

can't wait to try out the new designs thomas! thanks as always for your work!
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widdly



Joined: Jun 25, 2007
Posts: 266
Location: singapore
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PostPosted: Wed Nov 07, 2012 8:39 am    Post subject:   Reply with quote  Mark this post and the followings unread

Thanks for another great design Thomas.

I built it this afternoon on perf board and it works very nicely. Like the other TH designs I've built, the input ranges on all the controls are tuned perfectly.

Very Happy
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fonik



Joined: Jun 07, 2006
Posts: 3814
Location: Germany
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PostPosted: Tue Sep 22, 2015 5:17 am    Post subject: Re: Voltage Controlled Crossfader/VCA
Subject description: Another circuit for your consideration
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while looking around for a simple crossfader CV circuitry i found a very similiar on an old tom gamble EFM dual VCA, however, your solution is much more elegant and adds a nice touch with the overall volume control using the emitters!
thank you!

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elmegil



Joined: Mar 20, 2012
Posts: 1828
Location: Chicago
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PostPosted: Tue Sep 22, 2015 7:07 am    Post subject: Reply with quote  Mark this post and the followings unread

Excellent, thanks Thomas!

(Previous post deleted; still need the reminder not to post before finishing my tea)
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Sethkaine



Joined: Sep 26, 2015
Posts: 16
Location: Suisse

PostPosted: Mon Sep 28, 2015 2:48 am    Post subject:  expo converter Reply with quote  Mark this post and the followings unread

Hello Thomas,

I'm trying myself to your OTA designs : learning, breadboarding, etching, soldering, testing, listening. I love your designs from birthofsynth by the way. Wink

Sounds great to discover "new to my knowledge" designs in this forum. I'll going to try it out.

continue the good job and a big thank you for your schematics you're pleasing my ears.

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wackelpeter



Joined: May 05, 2013
Posts: 222
Location: germany
Audio files: 8

PostPosted: Tue Feb 02, 2016 12:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

Nice design Thomas, many thanks for that very cool circuit. Very Happy

It's not only a Crossfader or VCA also some kind of manual or voltage controlled wavefolder/mangler when you feed two waveforms from one VCO into it.

Like it thumleft

Makes me feel i need a second one... Smile

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richardc64



Joined: Jun 01, 2006
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PostPosted: Tue Feb 02, 2016 3:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

And still no love for mine.

http://www.sdiy.org/richardc64/mmvca/

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LFLab



Joined: Dec 17, 2009
Posts: 340
Location: Rosmalen, Netherlands

PostPosted: Wed Feb 03, 2016 3:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Which IS very interesting! Have you tried this with the LM13700 schematic already, Richard?
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roglok



Joined: Aug 28, 2010
Posts: 197
Location: uptown

PostPosted: Wed Feb 03, 2016 8:22 am    Post subject: Reply with quote  Mark this post and the followings unread

richardc64 wrote:
And still no love for mine.

http://www.sdiy.org/richardc64/mmvca/


thanks for the reminder, richard. i've meant to prototype your circuit but totally forgot about it...
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richardc64



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PostPosted: Fri Feb 05, 2016 8:13 am    Post subject: Reply with quote  Mark this post and the followings unread

LFLab wrote:
Which IS very interesting! Have you tried this with the LM13700 schematic already, Richard?


Negative, LF. I have other priorities. But anyone is welcome come to experiment with the idea: Capacitor couple the audio inputs, give it a better current source, perhaps with Lin-Log response.

Etc.

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wackelpeter



Joined: May 05, 2013
Posts: 222
Location: germany
Audio files: 8

PostPosted: Fri Feb 05, 2016 11:35 am    Post subject: Reply with quote  Mark this post and the followings unread

richardc64 wrote:
LFLab wrote:
Which IS very interesting! Have you tried this with the LM13700 schematic already, Richard?


Negative, LF. I have other priorities. But anyone is welcome come to experiment with the idea: Capacitor couple the audio inputs, give it a better current source, perhaps with Lin-Log response.

Etc.


Damn... that's what i forgot on my TH X-Fader because i couldn't wait to test it.... Smile didn't recognized the two blank holes on my frontpanel...

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sompost



Joined: Aug 17, 2010
Posts: 48
Location: Switzerland

PostPosted: Sat Feb 27, 2016 2:58 am    Post subject: Crossfader-only Reply with quote  Mark this post and the followings unread

Hi all,

I would like to use this great circuit as a voltage controlled mixer (crossfader option on sheet 1 above). Because the master level would always be set to maximum level, and envelope control would not be needed, the whole branch to the left of R11 (between Q1 and Q2) seems unnecessary for a crossfader-only use. Am I right?

What would I have to replace that branch with? Do I need the buffer (IC3c) or can I just supply +15V via some resistance to the point between Q1 and Q2? What would that resistance be?

Thanks!

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