A little taste of some Kansas home cookin' (VCF)

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Moog$FooL$
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Post by Moog$FooL$ » Thu Jul 11, 2013 5:47 pm

nice! :tu:
i might be interested when it's for sale.

thanx.
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Scott Stites
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Post by Scott Stites » Thu Jul 11, 2013 7:16 pm

What a world - VTL5C3 is the guy that made me think of trying a SVVCF based on the 2040 gain cell JH had worked out and René Schmitz later modified.

Negativspace has really tweaked it into a demon here, particularly in the refinement of the front end and control circuitry, and very particularly in the fact that he got self-oscillation out of the thing. He has massively embiggened the idea beyond where I went.

I've always loved State Variable filters for their multiple outputs, and have put together a number of them on the breadboard. But, I hope I don't sound too hyperbolic when I say I've never run across one remotely like this one. "Thick" was the word that came to mind when I thought of it, but Doc Sketch-n-Etch's "tonnes of character" more precisely defines it, I'd say.

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J3RK
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Post by J3RK » Fri Jul 12, 2013 12:40 pm

Very nice! This is still something I've wanted to build since I saw it on EM. I was originally going to build small PCBs for the discrete version of the gain cells, that could be used in various applications. I haven't gotten around to it yet because of other projects. I'd still like to do that down the road, but getting a board or two sooner... :party:

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negativspace
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Post by negativspace » Fri Jul 12, 2013 6:00 pm

Some SMD gain cell boards would be really cool... I saw that post and wondered if you were still planning to do it. 8_)

Scott, good to see you here! "Tweaked" is an accurate descriptor of what I've done; it's really just a couple of resistor changes to the schematic you posted. Grafting on the CP3 front-end turned out to be a fantastic plan, but all I really contributed there was to find a suitable value for the input resistor. :hihi:

I want to thank you again for giving me the keys to this thing. I'm looking forward to getting it out there.

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appliancide
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Post by appliancide » Sat Jul 13, 2013 11:38 am

I am building a 194 board right now. The plan has always been to add a simple mixer to combine the outputs, but I ALMOST used an opamp-based design! The CP3 looks like a much better fit, both conceptually (holy crap I'm a dork) and sound-wise. Are you still running it on +12/-6V? I assume you changed the input resistors to 100k?

Back to this awesome filter... it's the perfect companion module to the recent Thomas Henry/fonitronik modules. Great functionality, easy to find (and therefore also cheap) parts and an easy build with a faceplate PCB. I'm excited about this one. Nice job Jason and Scott!

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negativspace
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Post by negativspace » Sat Jul 13, 2013 4:18 pm

That's how I do my 194s too, but I just use a CGS04 for convenience. :sb:

No reason the CP3 wouldn't work, though. I kept all the resistor values in this one original, so 22k for the inputs. According to my 'scope even 10vPP signals don't clip until well past 12:00 on the dial so I left that alone. I managed the levels (remember, 2x gain) by using a rather large input resistor between the mixer and the VCF - it's 470k in the current build.

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regenbot
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Post by regenbot » Sat Jul 13, 2013 4:21 pm

definitely one for me, sounds great :yay:

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terrafractyl
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Post by terrafractyl » Sat Jul 13, 2013 6:06 pm

wow I'm Totally down for at least one board.

Sounds fantastic!! :hail:
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decaying.sine
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Post by decaying.sine » Sat Jul 13, 2013 6:15 pm

That's a beauty. I'll take 2, which means I'll take 4 :sb:
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Post by hiawog » Sat Jul 13, 2013 6:26 pm

wow, sounds great from the demo.

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negativspace
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Post by negativspace » Mon Jul 15, 2013 2:30 am

Thanks!

Here's an update so you all know where the project stands... my "prototype" is part of this, a special project I'm working on at the request of a friend. This board holds the CP3 + SVVCF and a Minimoog VCA:

Image Image

When I offer this filter as a PCB/module it won't be on this board - I'm going to be starting from scratch and the VCA won't be included. When finished it will mate to a daughterboard on .100 headers. The panel design for that module is in a very early stage:

Image

Feel free to offer input here... the mixer stage is brought to the panel so it can be used independently and all 3 filter modes get their own output jack. The only bit of unclaimed space is the jack labelled '???' - I'm thinking to make that one a 1v/oct CV input, but please let me know if you have another idea. (It could, for example, be a toggle switch that selects the + or - output of the mixer for input to the filter.)

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robot909
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Post by robot909 » Mon Jul 15, 2013 2:41 am

Filter sounds great. I would be down for a pcb.

Beautiful PCB work btw! :banana:

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negativspace
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Post by negativspace » Mon Jul 15, 2013 4:30 am

Thanks! It was no small task to cram all three circuits into a 16hp board... of course I went with a 20hp panel in the end, but at the time it made sense.
The only bit of unclaimed space is the jack labelled '???' - I'm thinking to make that one a 1v/oct CV input, but please let me know if you have another idea. (It could, for example, be a toggle switch that selects the + or - output of the mixer for input to the filter.)
... or it could invert the polarity of CV2? Is it bad form to reply to my own request for ideas? :lol:

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appliancide
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Post by appliancide » Mon Jul 15, 2013 9:10 am

If the mixer can used separately, won't the VCF need its own input?

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paperCUT
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Post by paperCUT » Mon Jul 15, 2013 9:51 am

Looks great, maybe a notch pot could be squeezed in there? :despair: It could be done externally but if you added it that would be used 95% of the time for me. If there's just space for a switch a x5 or x10 overdrive switch would always be welcome :nana:

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Post by Dego » Mon Jul 15, 2013 9:53 am

:sb:

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Isaiah
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Post by Isaiah » Mon Jul 15, 2013 10:32 am

Yes, a Notch output with LP-HP fade knob a la SEM would be a great addition.

Could one of the CV attenuators be bi-polar (attenuverting)?
It's just something I expect of SVFs and other multi-mode VCFs I guess.

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negativspace
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Post by negativspace » Mon Jul 15, 2013 3:38 pm

You know I've never once used a notch filter in 19 years of making electronic music? Never even crossed my mind... I always reach for an EQ when I want to cut a frequency band. :despair:

Shouldn't be hard to add, though, it's just a mix of LP and HP? I don't have space for both a jack and a pot (as you can see) so the balance control would be a no-go.

I do intend to make one CV input bipolar - whether as an attenuverter or with a polarity switch in the ??? slot.
appliancide wrote:If the mixer can used separately, won't the VCF need its own input?
Not as such... tapping the mixer output doesn't change the internal signal path, it just gives you extra options. I suppose if I ran the internal mix signal through the N/C lug of a jack in the ??? position one could use both sections of the module independently at the same time, which is what you're getting at. Good idea.

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Post by wavehead » Tue Jul 16, 2013 2:51 am

negativspace wrote:Thanks! It was no small task to cram all three circuits into a 16hp board... of course I went with a 20hp panel in the end, but at the time it made sense.
The only bit of unclaimed space is the jack labelled '???' - I'm thinking to make that one a 1v/oct CV input, but please let me know if you have another idea. (It could, for example, be a toggle switch that selects the + or - output of the mixer for input to the filter.)
... or it could invert the polarity of CV2? Is it bad form to reply to my own request for ideas? :lol:
i think a switch between the +/- mixer outputs to filter would be awesome and imo most useful thing in this position. the difference between the negative/positive outputs (the saturation/clipping difference between them) of the CP3 mixer is a pretty substantial change in timbre. it's always nice to quickly switch between something like this instead of patching it... a lot easier to discover differences you didn't know were there.

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plankton
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Post by plankton » Tue Jul 16, 2013 6:12 am

That sounds really good!

I'm in for 1 PCB

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Paradigm X
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Post by Paradigm X » Tue Jul 16, 2013 7:40 am

automated notch filters sound amazing, a bit like a phaser but .. not.

:party:

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Post by Monobass » Tue Jul 16, 2013 2:56 pm

Paradigm X wrote:automated notch filters sound amazing, a bit like a phaser but .. not.

:party:
the toppobrillo filter definitely opened my mind to what's possible with notch filters, very cool.

This sounds great Jason!
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negativspace
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Post by negativspace » Tue Jul 16, 2013 4:31 pm

Maybe I've just never had a good one... I tweaked the layout a bit and settled on the 'mixer +/-' switch in the ??? position. It occurred to me that I only need one mixer output on the bottom, since polarity is accessible via the switch, which frees up one more jack. Hey, notch output! :party:

I'll mull it over a bit before committing, but this layout satisfies most every request (even mine) so I like it.

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Post by Monobass » Tue Jul 16, 2013 4:35 pm

negativspace wrote:Maybe I've just never had a good one...
I think that's definitely the case with me and the Toppo. I think there is some kind of gain compensation going on the in the Toppo which is perhaps what makes it really bite.
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Post by frozenkore » Wed Jul 17, 2013 9:21 am

I'm definitely in for a set. Great demo!
Cheers!
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