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A new VCF! Half a Polyfusion VCF, simplified
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Hashtag Octothorpe



Joined: Jun 11, 2017
Posts: 16
Location: Grand Rapids MI

PostPosted: Wed May 02, 2018 2:03 pm    Post subject: A new VCF! Half a Polyfusion VCF, simplified Reply with quote  Mark this post and the followings unread

I love the sound of kick drums going through a resonant high-pass VCF, but my Sallen-Key variable-state-filters are too unpredictably screamy at high Q settings, and my most beautiful filter, a Polyfusion 4-pole HPF works super great, but the cutoff is too steep for this purpose.

So I decided to build half of a Polyfusion HPF (with opamp buffers instead of the FETs) simplified circuitry for the cutoff setting, and no voltage-controlled resonance.

I've got it working, and YOU GUYS it is SO GOOD. The resonance is utterly predictable and controllable. The self-oscillation goes from moving the speaker cone back and forth slow enough to see to ultrasonic with no harsh changes in volume at all, and the self-oscillation comes on so gradually.

Has anybody already designed a filter like this?

Once I get the values sorted out, I'll post schematics!

Here's the original Polyfusion HP VCF

My circuit in progress
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LFLab



Joined: Dec 17, 2009
Posts: 469
Location: Rosmalen, Netherlands

PostPosted: Thu May 03, 2018 1:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Well, if it is stable in that build from the picture, it is bound to be stable on a PCB Smile

Wow, maybe cast it in clear epoxy, as art? Very Happy
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AlanP



Joined: Mar 11, 2014
Posts: 490
Location: New Zealand
Audio files: 30

PostPosted: Thu May 03, 2018 1:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Very nice deadbug Smile
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Grumble



Joined: Nov 23, 2015
Posts: 721
Location: Netherlands
Audio files: 21

PostPosted: Thu May 03, 2018 1:34 am    Post subject: Reply with quote  Mark this post and the followings unread

LFLab wrote:
Well, if it is stable in that build from the picture, it is bound to be stable on a PCB Smile

I'm not to sure about that! Cool

_________________
my synth
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