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CD4007 voltage controlled filter?

Started by caress, December 16, 2006, 01:29:08 AM

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caress

December 16, 2006, 01:29:08 AM
has anyone ever tried this circuit?
any thoughts, ideas?

here's the circuit:


and the datasheet for the cd4007:
http://www.ensc.sfu.ca/reference/data-sheets/CD4007.PDF

Paul Perry (Frostwave)

#1
December 16, 2006, 02:20:28 AM
http://www.uni-bonn.de/~uzs159/ has another version of a 4007 based filter.

Tim Escobedo

#2
December 16, 2006, 02:47:05 AM
Seems like it would work. Labolida recently posted his Tiny Synth using that design, with sound samples. It is pretty much a Sallen-Key filter design. My only wonder is how much distortion there would be using those MOSFETs as variable resistors. Distortion which really shows up with relatively clean guitar like signals are sometimes masked when fed those brute synth waveforms.

gez

#3
December 16, 2006, 04:34:22 AM Last Edit: December 16, 2006, 04:36:42 AM by gez
Quote from: Tim Escobedo on December 16, 2006, 02:47:05 AMMy only wonder is how much distortion there would be using those MOSFETs as variable resistors. Distortion which really shows up with relatively clean guitar like signals are sometimes masked when fed those brute synth waveforms.

I once reworked the standard op-amp SVF design for use with a 4007.  Didn't take much to get it to distort.  Ended up having to divide down the signal into each integrator stage.  Worked well, slightly noisy (as you'd expect) and it was easier to use an OTA design in the end.   :icon_lol:
"They always say there's nothing new under the sun.  I think that that's a big copout..."  Wayne Shorter

caress

#4
December 16, 2006, 11:32:26 AM
anyone have any good circuits for filters?
lowpass, bandpass, notch, highpass, switchable, etc...

R.G.

#5
December 16, 2006, 12:36:55 PM
Do a google search for "state variable filter".

Also get a copy of Don Lancaster's "Active Filter Cookbook".
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

caress

#6
December 17, 2006, 12:56:40 AM
i got a copy of it already, but i'm working on a project that i want to add a lpf and bpf onto right now.  i need a little bit of time to get down the math for some of the filters... :P  filter design is very very new to me so i want to read through the book at least once and then mess around a bit.  for the time being, though, i need a filter that works...   :icon_wink:

slacker

#7
December 17, 2006, 07:01:56 AM
If you want something a bit different try the Synthacon VCF, it's a very cool sounding filter that can do lowpass, bandpass, highpass, notch and phaser sort of effects.
Here's one implementation of it http://www.cgs.synth.net/modules/cgs35_syntha_vcf.html
and here's what I did with it, with schematics and soundclips.
http://www.diystompboxes.com/smfforum/index.php?topic=45148.0
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