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 Forum index » DIY Hardware and Software » Developers' Corner
VCF-Module
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Parkchemiker



Joined: Mar 20, 2012
Posts: 11
Location: Berlin

PostPosted: Tue Nov 10, 2015 5:25 am    Post subject: VCF-Module
Subject description: Homemade vcf-module, a 4-pole voltage controlled lowpass filter
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Here you can see videos 4-Pole Filter


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VCF-Modul-Schem2.pdf
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VCF-Modul-Schem1.pdf
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Thomas Strauß · 10407 Berlin · diodenfilter@gmx.de

Last edited by Parkchemiker on Sun Jun 04, 2017 4:12 pm; edited 35 times in total
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Grumble



Joined: Nov 23, 2015
Posts: 577
Location: Netherlands
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PostPosted: Tue Nov 24, 2015 12:51 am    Post subject: Reply with quote  Mark this post and the followings unread

Just a small n00b quaestion: What does "FEEDBACK" do?
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beep



Joined: May 05, 2013
Posts: 101
Location: Germany

PostPosted: Mon Dec 14, 2015 6:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Grumble wrote:
Just a small n00b quaestion: What does "FEEDBACK" do?


resonance

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LFLab



Joined: Dec 17, 2009
Posts: 439
Location: Rosmalen, Netherlands

PostPosted: Tue Dec 15, 2015 8:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Nice frontpanel
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g.gabba



Joined: Nov 29, 2008
Posts: 174
Location: berlin
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PostPosted: Fri Jan 08, 2016 11:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello,
would you like to share your schematic?
cheers
gabbagabi
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Parkchemiker



Joined: Mar 20, 2012
Posts: 11
Location: Berlin

PostPosted: Sun Jan 31, 2016 4:55 am    Post subject:  Schematics
Subject description: VCF-Modul
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Hello gabbagabi,

yes, you can have the schematics for VCF-Modul, front parts, and the general purpose vcf - card for analog synthesizers.

To make the small numbers and signs visible, I printed the schemos in the format 1000mmX1000mm and smaller.

Thomas


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LTSpice simulation schemo
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4-pole-vcf.gif



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breadboard model of 4-pole-filter (8-diode-filter)
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8-Dioden-Filter.pdf
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Revision 1 - changed values of 5 resistors for better resonance behaviour (sine wave generation up to 20KHz)

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Thomas Strauß · 10407 Berlin · diodenfilter@gmx.de

Last edited by Parkchemiker on Mon May 29, 2017 9:00 am; edited 8 times in total
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g.gabba



Joined: Nov 29, 2008
Posts: 174
Location: berlin
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PostPosted: Mon Feb 01, 2016 10:08 am    Post subject: thx Reply with quote  Mark this post and the followings unread

Hello Parkchemiker,
thx for the schemo.
It looks interresting, like a new filter concept.
And in my opinion we need new concepts!

Probably will put it in Multisim the next days.
The CV range is 0V to 10V?

regards from africa to my hometown Smile
gabbagabi
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Parkchemiker



Joined: Mar 20, 2012
Posts: 11
Location: Berlin

PostPosted: Tue Feb 16, 2016 6:23 am    Post subject: VCF
Subject description: Control-Voltage
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Hello gabbagabi,

the control voltage is from 0...12V for the keyboard voltage, and 0...12V for the Cutoff-Voltage. The Cutoff-Voltage is regulated by a stereo-pot (2 X 10K lin), one for the Cutoff-Voltage, one for the ADSR-Voltage). The bigger the Cutoff-Voltage, the smaller the ADSR-Voltage and vice versa - this is to avoid an overdriving of the diodes.

Greetings from Berlin

Parkchemiker

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Thomas Strauß · 10407 Berlin · diodenfilter@gmx.de
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g.gabba



Joined: Nov 29, 2008
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PostPosted: Thu Apr 07, 2016 2:51 am    Post subject: Reply with quote  Mark this post and the followings unread

dear Parkchemiker,

I have simulated your schema in Multisim and I was pleasantly surprised by the operation of the filter stage.
The following Breadboard test has the simulation fully confirmed.

I immediately had ideas for the use of the principle in other filter topologies.

If you do not mind I'll post it here on EM and refer to this thread.

Do you have a name for your filter?

cheers
BB
gabbagabi


Parkchemiker Diode VCF 6dB Stage.png
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elektrouwe



Joined: May 27, 2012
Posts: 104
Location: Germany

PostPosted: Fri Apr 08, 2016 4:23 am    Post subject: Reply with quote  Mark this post and the followings unread

g.gabba wrote:

Do you have a name for your filter?
gabbagabi

I'm sorry, but there is nothing new with this filter concept. Look at Steiner's 70's diode filter and you can see the same diode-C arrangement. Diode based VC-attenuators have a long history in VCA and VCF design and many variants exist. BTW you can improve distortion/dynamic range by putting 2 or more diodes in series or using LEDs (although matched LED pairs are much harder to select). Diode attenuators have the advantage, that you get the V/oct (exp.) for free, but temperature compensation is easier to get with matched transistors. That's why most diode ladder filters do not apply CV to the diodes but use an extra transistor based expo to control the diode current.
Nichts für ungut Wink
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Parkchemiker



Joined: Mar 20, 2012
Posts: 11
Location: Berlin

PostPosted: Sun Apr 10, 2016 5:11 am    Post subject: VCF-Module Reply with quote  Mark this post and the followings unread

Hello gabbagabi,

I call the filter "diodenfilter".

My circuit uses diodes as voltage controlled resistors - this is not a new principle.

The filter capacitor is grounded in my circuit - what is not the case in the Steiner - filter.

I think the special about my "diodenfilter" is the minimum of electronic components and that only one half of the diode bridge is fed with an audio signal, what leads to another equivalent circuit as in related vcf-circuits.

This filter has a registered design:

Google: utility patent


cheers Parkchemiker

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Thomas Strauß · 10407 Berlin · diodenfilter@gmx.de
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