5-Band Fully Parametric EQ

[aziltz]

I would like to contribute something I've been working on.  I have not built it yet, but I'm going to very soon.  

If you see any issues with the design please let me know!

This is a 5-Band Eq that I've concocted from the ideas RG listed at Geofex - http://www.geofex.com/Article_Folders/EQs/paramet.htm

It uses FET-based Gyrators, which I have not seen before, but I really dig FETs.  I choose these over Op-Amps for a simpler wiring scheme.

This also features parallel inputs, and input and output trim (for active pickup basses).  The first and last stages could be dropped if this is not needed.  I used both because the summing amplifier is an inverter.

I wrote, Copyright Austin Ziltz 2009 on the schematic, but I wasn't really sure if I needed to point to geofex, or anything like that.  The ideas are not new, but the drawing was done by me.  Please advise me if this should be adjusted, I don't want to step on RG's or anyone else's toes!

It's still being tweaked, and the caps for the Band Ranges have been left unlabeled.  For info on how to select though, please see RG's great article above.
I'll be adding a pcb layout for it eventually.

Thanks,

[dschwartz]

looks interesting.. have you simulated it?

[aziltz]

I did.  I'll post my results tonight.  It looks like the FET in that configuration doesn't quite work.  I get more of a shelf response, where the slope on the high frequency side of the band is also amplified.

Swapping out the FET's for BJT's works like a charm though, and I may have to do that.  I think my issue with the FET is that I thought it was a simple follower, but perhaps the fact that the signal can't swing very far negatively impacts the gyrators L on one side of the band.  Just a theory.  I'll have to simulate it with a BiPolar Power Supply and see where I get.

There is some trickyness to locating the Ranges and C values though.  I recommend using J. Orman Gyrator Calculator, http://www.muzique.com/lab/gyrator.htm

There are different combinations of C's that give you the same frequency ranges, but the Q will vary drastically so watch out for that.


BTW, is there a decent version of 5Spice for the Mac?  I just got a new computer.

[aziltz]

I can't access my simulation files right now, but the conclusion was the FET Gyrator does quite work.  The BJT Gyrator is a little iffy as well.  The maximum Boost/Cut seems to vary with the frequency quite a bit, as well as Q to a less degree.

In other news, RG's original design using OpAmps simulates like a dream.  The Q varies every so slightly with frequency, but the amplitude (boost/cut) is dead constant.

So here's version 2.  Probably the one I will be using until I can develop some kind of FET Gyrator (for gits and shiggles).

[jkokura]

have you gotten to the point of creating a PCB layout yet?

[aziltz]

have you gotten to the point of creating a PCB layout yet?

Yes, I'm still tweaking it though.  Perhaps by the weekend I'll be happy with it.  I will probably etch some prototypes then.  I have a few small changes to make to the circuit.  It will be extremely universal though, something you can use all or some of it to achieve different goals.

Also, I'll post a new schematic soon.  I've added a few things including using the last opamp for Vref

[welcomb]

Just a quick question, why do you need 4 opamps (2 x NE5532) in the "signal path"?

Isn't IC1B and IC2A sufficient?

[jkokura]

I have a 10 band from BYOC, but I prefer parametric for acoustic guitar. I was thinking a 3 or 4 band would be great, but a 5 band could be really amazing. Low, mid low, mid, mid high, and high fully parametric bands! Looking forward to this one.

Jacob

[aziltz]

Just a quick question, why do you need 4 opamps (2 x NE5532) in the "signal path"?

Isn't IC1B and IC2A sufficient?

Yes they are sufficient.  However, the person that prompted me to design this wanted dual inputs, and I wanted Input and Output Trimmers.  The summing Amp used is inverting, and the middle two stages are non-inverting so I made the final stage inverting.  Overall, the circuit is non-inverting.  You could drop the outer Op Amps and just put the input at C1 with a 1M pull down resistor and take the output from C2.  I *think* this will give you unity gain, but I think its best to have trimmers.  A 1M Volume Pot Wired at the input would work as well.

Also, I didn't make this change, but I think TL072 (JFET?) should go in the signal path at the input/output and put the 5532's in the Gyrators.

I'm building this for two friends right now.  I will probably refine it over my christmas break as well.  I'm still planning to etch this weekend so I'll post some layouts then.


jkokura, the nice things about the way this is set up is, you can take the same layout for the full 5 bands and only populate as many bands as you want, and trimpots can become knobs and vice versa.  I'm building two slightly different versions right now using the same PCB.

Just for reference, here's a slightly updated schematic, and a board layout to go with it, just to show the scale and component placement.  I have to do some more simulations before I can recommend cap pairs and frequency ranges, but the opamp gyrators behave really well.  I've also removed the earlier versions from the web.

[Brymus]

Nice 
I like what you have done here.
Looking forward to more.

[welcomb]

Ah you're using trimmers for Q and f.

I'm going to have pots for both Q and f, and wonder how many bands I can fit into a 1590BB. I got my PCB designed months ago, just procrastinating with actually etching and drilling my enclosure. And still thinking what freq bands is useful for bass.

[earthtonesaudio]

If you use those tiny pots like in the Zvex "Seek" series, you could fit 2 rows of 8 with room for footswitches.

Or you could do like the Blackstone Mosfet overdrive and use submerged pots with flush-mounted "fingernail adjust" knobs.  I think you could fit 5 rows of 3.

[aziltz]

Ah you're using trimmers for Q and f.

Yes, I used trimmer's in the layout, but I'll be using those pads for pots as well. It's really no different, the sizes are the same.  

I'm building two versions, one with 5 Level Pots, 3 Frequency Pots and the rest are trimmers and the 2nd has 5 Levels, 5, Frequencies and 3 Q's all external.  I'm going 3 Rows of 5x 16mm pots in the big 1790 with this project.

As earthtones said, you can get small pots and fight up to 16 in a 1590BB.  Using 16mm Pots, You can easily fit 5 across, and possibly 2 rows if you use board mounted pots, so the PCB fits under it.

This is just the first iteration.  I will probably redo it to accommodate board mounted pots, both 16mm and the smaller Zvex-style ones.

I'll post what I decide for bass frequencies over the weekend.  Here's mockup's of the drilling layout of the 1790-projects using this PCB and 16mm pots.

[aziltz]

It just occurred to me that the best name for this project is probably, Box of Knobs.

For reference, here's a 1590BB with 5 16mm Pots across.

[welcomb]

Woah that's a nice layout pic. Thanks!

btw what software did you use to design that?

[aziltz]

Woah that's a nice layout pic. Thanks!

btw what software did you use to design that?

Thanks, I used Google Sketchup, the free version.  It's very easy to make a box to scale, mark holes and then extract measurement dimensions like I've done there.

[jkokura]

I think I'd build a 4 band eq, with the Bass and Treble controls only being level and Q, and the two mids being Level, Q and freq.

I'd build it in a BB if I could, but depending on the size of the PCB that's not really necessarily going to fit. the 1790 would do with that setup.

However, a DD would easily fit all 5 bands fully parametric with room for a boost/mute switch too, perhaps a tuner out. This would fit my acoustic need pretty well, especially the cut. It could remove the need for a volume pedal with the cutoff and tuner out...

[aziltz]

I think this project would allow you to do that quite easily. Keep in mind, without board mounted pots there will be quite a lot of pot wiring. I'm planning on using twisted pair and triplets with zip ties to minimize the rats nest in the 1790NS. With board mounted 16mm and miniature board mounted pots I think you could fit it in a BB.

[jkokura]

I hate to be a bother if this isn't possible, but is it too much to ask you to design a layout that features:

16mm board mounted pots for 4 bands level and Q, and for the mid low and mid high freq, as well as trim pots for the true middle? I have little experience with layouting, and have barely been able to create schems in Eagle, forget creating my own layouts.

I think I'd also want a layout that featured a fully parametric setup up with 3 16mm board mounted pots per the 5 bands to drop in a 1790 or DD that I could add a bypass, mute and tuner out to. I'd build them both I bet.

But again, if that's asking too much...

[aziltz]

I hate to be a bother if this isn't possible, but is it too much to ask you to design a layout that features:

16mm board mounted pots for 4 bands level and Q, and for the mid low and mid high freq, as well as trim pots for the true middle? I have little experience with layouting, and have barely been able to create schems in Eagle, forget creating my own layouts.

I think I'd also want a layout that featured a fully parametric setup up with 3 16mm board mounted pots per the 5 bands to drop in a 1790 or DD that I could add a bypass, mute and tuner out to. I'd build them both I bet.

But again, if that's asking too much...

Short answer yes, but I wasn't planning to do it this month.

I'm planning to do just that.  A few iterations with board mounted pots.  Right now I'm not sure when I'll get to it as I have to build two versions before mid-december using the board here.  I was already planning to work on board-mounted pots over christmas break.