via gmeredith on this electro-music.com thread where you will find more info. "Well, I've just completed a huge project, which has been on my mind for a while now, ever since finding this forum - to build a true polyphonic, 4-voice VCF module, with CV input and resonance, running off 9V DC.It has taken me about 3 months of spare time to get this thing researched, thought out, breadboarded, built and optimised for the Casio SK sampler keyboards (I have an SK8). But it has finally come!!
Below are the results of my efforts.
But I wanted specially to post this message, in order to say a big THANK YOU to everyone in this DIY community; for both directly and indirectly helping me with this project by the way of advice, and links to circuits and information.
I especially want to thank Tim Escobedo, who designed the Q&D VCF, from which this quad VCF is wholly adapted from. Using it as a starting block got me half way there in one hit! Thanks to all the people here who put me on to it!!
I've written up a complete illustrated guide on how to make this quad VCF, which I call the "PHAT PHILTER BANK", and how to set it up for the Casio SK series keyboards. The guide is here, at the bottom of the page here:
http://www.jz-server.de/forum2/e107_plugins/forum/forum_viewtopic.php?559
[Update: this original link appears to be dead. This updated link was added to the thread. Be sure to check the electro-music.com thread linked above for updates.]
There is also on that page an mp3 example of one of the SK presets with the filter applied. Makes the humble SK-8 sound like a real analog synth!!
You can also make it as a stand-alone unit, or adapt it to another type of keyboard, although another keyboard may or may not be able to take advantage of the full features that this VCF unit has - such as CV input. The SK samplers have separate internal envelope CV signals for their VCA's, which is particularly useful for driving this VCF. The guide shows you how to set it up in various ways.
Again, thank you all SO MUCH for sharing the knowledge that enabled this to happen!!
Cheers, Graham"
