parametric equalizer has anyone built one, got a layout

[geoffro]

Hi,
been reading rg's site about parametric EQ http://www.geofex.com/Article_Folders/EQs/paramet.htm#variable_l
just wondering if anyone has built one or knows where i can find a layout for one
thanks
geoff

[newbie builder]

I'll bump this because i'm very curious too. I've got a t.c. electronics dual parametric e.q. pedal and a t.c. electronics 1140 (4 band parametric eq) and i love them both, but have never found a diy design like them.

[geoffro]

thanks dude.
i have been searching the forum and beyond,
but i think there is enough info from geofx to do it i just am not experienced in layingout
but when i can come up with something i will post it to get the experts to check it over for me

i am sure there has been a fair bit of talk on here about them.
cheers
geoff

[Mark Hammer]

Craig Anderton had a design for one in Contemporary Keyboard magazine several decades ago.  I built it and liked it.  Though the circuit at GEOFEX suggests otherwise, a great many of the parametric EQ circuits/designs are based around a basic state-variable filter topology, not unlike the filter in a Mu-Tron.  As such, they require two resistances to be varied simultaneously to move the centre frequency around.  That, in turn requires a dual-ganged pot, which some folks find a deterrent (though it needn't be).

The larger question is whether a parametric will give you what you desire.  If the goal includes notching out feedback or wolf-tones, then the more precise continuous frequency tuning, and potentially narrower bandwidth, is a real boon.  If the goal is simply adding presence or resonances and voicing, then something simpler may suffice.  So-called "quasi-parametric" circuits (frequency and cut-boost but no Q/bandwidth control) can be useful too.  Heck, even something like the Anderton Mid-range booster discussed in another thread here can be quite useful, and VERY easy to put together.

So, what do you need it to do for you?

[Morocotopo]

 Peoples, I built the Geofex param EQ. It works OK, but the controls sweep in freq is a bit small, good for some uses (precise freq setting), not so good for others. The article details (I think) how to modify the freq sweep and/or freq range for each EQ section, but I found it a bit too much for my limited knowledge.
I also built a one section parametric EQ that is in, I think, experimentalists anonymous page archives, taken from some ¿japanese? schems book. That works good also, bigger freq sweep. I posted the layout and schem here, it should be available still, so SEARCH!

Morocotopo

[stephanovitch]

I have built this one: http://damien.douxchamps.net/elec/param_eq.php

with a pcb that i have redraw

[stephanovitch]

http://www.neufgiga.com/index.php?m=30a162f4&a=50c2346d&f=136105014

[John Lyons]

+1 on the State variable filter (Craig Anderton's "Super Tone Control"). It really can shape your sound in radical and subtle ways.
Forgot to mention that to you earlier Geoffro...

If you do a search here for State Variable filter and or Craig Anderton you should come up with a post and build report I did on the one I made. It had sound clips I believe as well.

John

[stephanovitch]

http://www.neufgiga.com/index.php?m=30a162f4&a=50c2346d&f=136131705

[donald stringer]

http://www.sound.westhost.com/project64.htm  I built this one, really cool possibilitys. You can make it with as many or as few filters, for mine I used ten and housed them in a simple aluminum box. Whats so good about it is you can totally eliminate a particular freq. if you so prefer.

[geoffro]

Hi donald,
i was looking at this yesterday, do you have any pics of your build at all.
i would love to see some.

mark,
What i initially want this for is to fine tune the accoustic pedal i have made so that my humbuckers will sound a bit better with it.
and i thought a parametric eq looked far more flexible than a graphic.

i'm thinking maybe the one donald is talking about might do the trick for me a little better as it allows you to totally eliminate a particular frequency (range i presume).

morocotopo, i did see the jap parametric  eq circuit and pics you posted. with that it has adjustable q? and adjustable boost/cut and 1 set on frequency adjustment Ra and Rb, i take it that these Ra and Rb go to the ganged pot?
so you adjust the frequency to where you want it and then widen or narrow the q and then boost or cut the frequency? lets say you wanted to have 3 seperate controls for the frequency like a normal tone stack does this mean you will have 3 lots of q adjustment and 3 lots of boost and cut?
cheers
geoff

[stephanovitch]

http://www.neufgiga.com/index.php?m=c9ae77e8&a=7d397569&share=LNK229447111b649b747

[nisios]

im actualy macking one at the moment.
at this point it is only on paper.....im making a publishable schematic and layout with diylayout creator.
it will have 3 variable bands and a fixed one. covering low, mid low, mid high and fixed (switchable) high shelf.
ill post it here as i go.

[geoffro]

nisios, that would be great to see
looking forward to it.

btw stephanovich all the links you are putting in here i cant get to work.

cheers
geoff

[alfafalfa]

Stephanovic ,

I can open your links and am waiting for your pcb design without the lettering in it.

I would like to try this one.

What would be the most noiseless opamps ? Right now I'm considering the NE5532 opamp ( dual opamp)

Wouldn't the noiselevel be lower than with the TL082 ?

Alf 

[cheeb]

I've been mildly obsessing over getting a Maestro Parametric Filter for some time now. Anybody know anything about those?

[nisios]

Here is the schematic i ve just finished doing.
Its made on switchcadIII wich im just learning how to operate at the moment.
not very pretty as it is.

This is not checked and not tested.
I have just done the math and i even find the high shelf filter is wrong as it is....i used the paralel filter formula and not the series filter formula to get those values.
I have some doubts on that area so....if soemeone could help me there it woud be great.
I will try to run a simulation as i learnshow to do that propperly on SCIII and breadboard it too.
Ill post as i go.
This desigs was inspired on the ESP parametric project and also geofex data on this subject.

[stephanovitch]

sorry for this poor link.
Let me know If this new link is not active: http://www.neufgiga.com/index.php?m=c9ae77e8&a=7d397569&share=LNK768647150729844ff
I have redrawn it, it's one of my first PCB 6 years ago.
The NE5532 and NE5534 are good audio OPamps with low noise, best than the TLO82

[stephanovitch]

Layout + PCB:
http://www.neufgiga.com/index.php?m=c9ae77e8&a=7d397569&share=LNK32474717adfa61678