Author Topic: State variable parametric eq layout/pcb  (Read 479 times)

st2

State variable parametric eq layout/pcb
« on: January 21, 2021, 06:18:27 AM »
Hi everybody, electric violinist here trying tinkering with DIY effects  :icon_wink:. First of all, thanks for the wealth of info I've found here over the time. Great forum  8).
I'm building a simple high impedance buffer (jfet+bjt) to make my instrument active (embedded piezo). Then I want to build a simple "universal" opamp preamp with active volume and sweepable tone controls, plus a pair of parametric state variable EQs. I don't have any experience laying out a PCB and so I'm looking if I can find some premade "building blocks", especially for eq.
I found BYOC did make a PCB with state variable parametric eq filters but unfortunately it's out of stock  :icon_rolleyes:
Do you know of any ready made PCBs or layouts for state variable parametric eqs?
Thanks a lot.

garcho

Re: State variable parametric eq layout/pcb
« Reply #1 on: January 21, 2021, 11:38:06 AM »
Welcome to the forum! Especially nice to have a violinist around here.

You'll find quite a lot of non-guitar pedal audio designs are made for bipolar power supplies, like 12 or 15V. Do you want this to be powered with a standard guitar pedal power supply?

Here is some good reading:

http://www.geofex.com/article_folders/eqs/paramet.htm
https://sound-au.com/articles/eq.htm

You might find something here:

https://www.elby-designs.com/webtek/cgs/cgs.htm

You're in the US?

I just found this, too, I believe it's from a forum member:

https://diy.thcustom.com/shop/3-band-parametriq-eq-full-control-pcb/
« Last Edit: January 21, 2021, 11:41:53 AM by garcho »
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st2

Re: State variable parametric eq layout/pcb
« Reply #2 on: January 21, 2021, 11:58:36 AM »
Hi Garcho, I'm from Italy. Thanks for chiming in. And sorry for my weak English.
Power supply will be 9V but I want to integrate a +9/-9 charge pump in the pedal. Probably a 3PDT + charge pump mini board.
ESP and Geofex are among my mandatory reads and I simulated on Simetrix a number of eq circuits.
I noticed that TH board but I'd like to avoid gyrator-based eq because I don't like Q changing along with frequency.
If I wanted a "tone control" eq type I believe I'd go with a Wien bridge, but I often use a -1 and -2 octaver with my 5-string violin (bass-like sound) and sometimes I neeed rather surgical eq to tame resonances. So I thought state variable is the way to go.
That link on elby design gives me security alert, is that safe?

garcho

Re: State variable parametric eq layout/pcb
« Reply #3 on: January 21, 2021, 12:17:48 PM »
Quote
That link on elby design gives me security alert, is that safe?

I don't get any alert, with Opera, Firefox, Chrome or Edge.

Quote
Hi Garcho, I'm from Italy. Thanks for chiming in. And sorry for my weak English.

I love Italy! And your English is fantastic, bravo.

Quote
but I often use a -1 and -2 octaver with my 5-string violin

I play a lot of Turkish music, they do that all the time, on clarinet, too, such a cool sound.

Quote
I'd like to avoid gyrator-based eq because I don't like Q changing along with frequency ... So I thought state variable is the way to go.

State variable is a type of filter, not EQ. Are you looking mostly for a notch filter? State variable filters have topography allowing you to tap LP, BP, or HP. 
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st2

Re: State variable parametric eq layout/pcb
« Reply #4 on: January 21, 2021, 01:52:54 PM »
Getting an alert with Firefox, perhaps it's geographic-related. I'll try in some other way.
You know that parametric Eq with state variable filters is done taking the bandpass out only, bonus is total indipendence of frequency, Q and boost/cut. No other bandpass or notch filter can do the same, apparently (I simulated most). Wien bridge is good but has a fixed 1.3 Q which is too broad in some cases.
https://sound-au.com/articles/state-variable.htm#s30


Ben N

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Re: State variable parametric eq layout/pcb
« Reply #6 on: January 21, 2021, 02:18:08 PM »
The aion Lumin, based on the bbe Sonic Stomp, is kind of a specialized SVF. It really focuses on the very highs and very lows, but if you socket the relevant caps you can experiment with it.

st2

Re: State variable parametric eq layout/pcb
« Reply #7 on: January 21, 2021, 02:55:52 PM »
http://musicfromouterspace.com/index.php?MAINTAB=SYNTHDIY&VPW=1910&VPH=809

https://shop.musicfromouterspace.com/cart/MFOS%20VCF%20State%20Variable%20Synth%20Module%20Bare%20PCB

Thanks, good finding! Unfortunately, this is made for working with control voltages, so half of the board is useless for me. Worth some musings anyway.

st2

Re: State variable parametric eq layout/pcb
« Reply #8 on: January 21, 2021, 02:59:13 PM »
The aion Lumin, based on the bbe Sonic Stomp, is kind of a specialized SVF. It really focuses on the very highs and very lows, but if you socket the relevant caps you can experiment with it.

Thanks, I saw that, similar to Anderton's Super Tone Control too I believe. That's the "other way" of using a state variable, with L, M, H outputs (like a xover). The parametric eq version requires a different circuit arrangement.

garcho

Re: State variable parametric eq layout/pcb
« Reply #9 on: January 21, 2021, 03:16:56 PM »
sounds like it's time to learn how to make your own layouts :)

there are these filter ICs available, on the Continent, too.
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st2

Re: State variable parametric eq layout/pcb
« Reply #10 on: January 21, 2021, 04:04:11 PM »
sounds like it's time to learn how to make your own layouts :)

You're right, I should bite the bullet but I'm very hesitant. I've been chasing Mr. Keen's book on PCB layout for a while but appears unobtainium. Do you know if there's a way to get it?
Thanks for your good advice

Ben N

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Re: State variable parametric eq layout/pcb
« Reply #11 on: January 21, 2021, 04:29:58 PM »
Thanks, I saw that, similar to Anderton's Super Tone Control too I believe. That's the "other way" of using a state variable, with L, M, H outputs (like a xover). The parametric eq version requires a different circuit arrangement.
Sorry, I missed that you wanted it parametric. Good luck!

jackwithoneye

Re: State variable parametric eq layout/pcb
« Reply #12 on: January 26, 2021, 12:58:30 PM »


http://www.geofex.com/article_folders/eqs/paramet.htm
https://sound-au.com/articles/eq.htm

https://diy.thcustom.com/shop/3-band-parametriq-eq-full-control-pcb/

Man, thoses links you'd posted are just what i was looking for, litterally for weeks. Still not perfect though, i'm tweaking values and try to find the right balance, but it already rocks, and i'm sure i'll find the right set up to integrate a good parametric eq into my next project, thanks to you