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CV Control for the CGS/Serge Resonant EQ...
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author CV Control for the CGS/Serge Resonant EQ...
tuanuibi
Hi guys,

Anyone done this? I'm thinking of having a separate panel for CV ins, but I'm not sure of the best way to go about it. Any ideas?

This thing sounds amazing! CGS Resonant EQ Page

Cheers,
Josh
CLee
Given the way the module is designed I don't think there is any easy way to voltage control it. If you look at the schematic each band's pot sets a balance between the input and an inverted signal from the output, which then goes to that band.

VC would be complex. Maybe Vactrols if you're energetic...
tuanuibi
Thanks - I think I'll go with vactrols, got a bunch lying around.
Cheers
Josh
Siri


Any thoughts on how to do this? It would be such a crazy feature Dead Banana
thermionicjunky
It could be done properly with 10 crossfader circuits in place of the pots.
GrantB
Something I've always wanted to try but still haven't got around to building is two RESEQ with one crossfader. That way I could use one CV to crossfade between two frequency response profiles. Someone who has the modules should make a demo of this Guinness ftw!
windspirit
I was thinking that just using 10 vactrols to affect the tuning of all 10 bands simultaneously would be the easiest thing, that way you can "sweep" the EQ shape across the spectrum. I have no idea if it would actually sound good though.
notmiserlouagain
You´ll need crossfaders for vc cut/boost. for changing the cutoff off the filters, it´s a bit awkward to do it with a vc resistors, because they are multiple feedback filters, and to change their cutoff with just one resistor will also change their gain/q aka bandwith.
MFB-Filter-Info
Siri
Would the suggestion on this link be a good idea?
https://www.muffwiggler.com/forum/viewtopic.php?p=1548097#1548097
jules
notmiserlouagain wrote:
You´ll need crossfaders for vc cut/boost. for changing the cutoff off the filters, it´s a bit awkward to do it with a vc resistors, because they are multiple feedback filters, and to change their cutoff with just one resistor will also change their gain/q aka bandwith.
MFB-Filter-Info


Yes, yes and yes. Plus you need a multiple cross fader for both band on each side of the one you want to change.

And I'm quoting myself: "this "eq" is designed as a network of filters which feed back on one another. Trying to add CV control to the bands amplitude would be total chaos: changing one band would have probably more effect on the other bands than the CV'd one"

Solutions:
=> Use VCAs on the individual outs of the bands.
=> Have a look at 4ms multi band/ spectrum module. Looks like it's doing what you want. Plus its code is open source.
=> Cwejman QMMF4: also called 42.
Siri
Quote:
And I'm quoting myself: "this "eq" is designed as a network of filters which feed back on one another. Trying to add CV control to the bands amplitude would be total chaos: changing one band would have probably more effect on the other bands than the CV'd one"


total chaos, i don't know, the idea would be to simulate/replicate the movement you're doing when you move the slider manually.

Quote:
Solutions:
=> Use VCAs on the individual outs of the bands.


that's a good idea, i forgot that you can tap the outs of each band (i didn't do the mod on my module). but then, as you said, it won''t affect the other bands like it does when i manually move the trimpot.

I don't have the knowledge to create such a circuit but if someone comes up with a schematic (the hardest part, i know) i can do a pcb layout of it and share it here (and modify it as suggestions would arise)!
PWM
You could mix the VCA outputs (upper, lower, all) as shown in the original schematics. Some values have to change, probably, but it's doable.

I expiremented with this some time ago. Upcoming weeks I'm fairly busy, after that I'll get my VCA breadboard out and see where I left of.

EDIT: VCA's at the output stages won't work - what was I thinking?! This wil set the volume of every band. It's not useless, but it's no VC over the band's frequency.
Crossfaders are the only way to go, I'm afraid, this means you need 2 VCA's per band.. Doable, still, but somewhat expansive.
Siri
PWM wrote:

Crossfaders are the only way to go, I'm afraid, this means you need 2 VCA's per band.. Doable, still, but somewhat expansive.


So it's like what, 10x TL074?
negativspace
No... far, far more complicated than that. Go find a VCA schematic and them imagine 20 of them, you'll begin to understand the scope of the problem.
Dogma
CV over everything isnt the Panacea i think people think it would be - i think this circut is a perfect example of that....it wasnt designed with CV the bands "frequency" - as already mentioned it would be choatic mush..

Check the ADDAC 601 for the closest i think you could get - amplitude maybe via a billion VCAs - but frequency - i dont see how it would or should work n the Serge EQ
Siri
Well that explains why nobody spent time on it eek! thanks for the explanations.

One more question, because i guess it can help others who think about it :

What about what they are suggesting in this thread?
http://www.electro-music.com/forum/topic-37628.html
about the suggestion in the last post, using two 2N5457?

(link for the MFOS schematic using 2N5457 : http://www.musicfromouterspace.com/index.php?MAINTAB=SYNTHDIY&PROJARG= WSG2010/wsg_page9.html&CATPARTNO=WSG001&PN=1&SONGID=NONE )
(Reseq page : http://www.cgs.synth.net/modules/pic/schem_cgs202_res_eq.gif )

I was thinking that if you stick to replicate exactly what's happening when you move the slider (one resistance goes up, the other one goes down - in a linear way, so vactrols would not be a good candidate), it should not be chaos, no?

Or a teensy maybe could do that?

thanks
1n
Sorry for reviving an oldie that was resolved zombie

I can't find any threads about making a CV breakout for the Random Source version, for movulating feedback. I can't read circuits, so don't know how different the CGS and R*S ones are.

Wondering whether anyone has done this and made it work?

Thanks
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