has anyone ever tried this circuit?
any thoughts, ideas?
here's the circuit:
(http://i82.photobucket.com/albums/j255/btroniq/4007basedVCF.jpg)
and the datasheet for the cd4007:
http://www.ensc.sfu.ca/reference/data-sheets/CD4007.PDF
http://www.uni-bonn.de/~uzs159/ has another version of a 4007 based filter.
Seems like it would work. Labolida recently posted his Tiny Synth (http://www.sdiy.org/labolida/) 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.
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:
anyone have any good circuits for filters?
lowpass, bandpass, notch, highpass, switchable, etc...
Do a google search for "state variable filter".
Also get a copy of Don Lancaster's "Active Filter Cookbook".
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:
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 (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 (http://www.diystompboxes.com/smfforum/index.php?topic=45148.0)