Simulated inductors - Girator ???

[nisios]

Hello everyone.
This is my first post on this forum.
I have to say i find it very nice and informative.
I consider myself a begginer on electronics and the first few things i did were stompboxes. I have a few notions now so now i decided to design my first distortion pedal.
I find it nice to play with the clipping diodes and that stuff but what i would really like to put in the stompbox is a nice sounding filter/eq.
I was looking for studio console filters to adapt when i found a guitar intended filter that i tested and liked very much...... It was on the stompboxology papers.
It uses a simulated inductor wich gives a very pleasing resonant tone.... i hate first order passive filters......they just seem to kill the sound to my hears.

Now im intrigued with this simulated inductor or impedance stuff and i cant find any info on it.

I would very much like to be able to calculate precise cutoff frequencies....

I can allways do it by hear but i would like to understand the concept behind it

Does anyone know any formula or calculators for this simulated inductor stuff?

Any info at all.

Thts it.

Thanks for all the info you guys have here.

Nisios

[d95err]

Just google for "gyrator" and you'll find some info. You'll find the appropriate formulas with the circuit more often than not.

Here is a good place to start...
http://en.wikipedia.org/wiki/Gyrator

[slacker]

Welcome aboard 

There's a good article on gyrators here. http://www.geofex.com/Article_Folders/EQs/paramet.htm
Well worth looking round the rest of that site, it's full of good stompbox stuff.

[lvs]

And another one...
http://www.bbc.co.uk/rd/pubs/whp/whp-pdf-files/WHP093.pdf

[nisios]

Thanks very much for all your help!

I just realized In fact this was my second post here....so...sorry for the double introduction.

Ive done some reading with all this stuff you pointed out and decided to go for an opmp gyrator......i was inicially thinking about making it with a transistor.

I then googled for a bit and eventually came across a schematic from an UREI equalizer. I used it to make the eq for the distortion and i like the sound very much.

Here is the pedal as it is now......I will try it with +-9v to see if there any significant improvement to the sound.

Im open to any sugention ... and it would be great if someone would try it....and make a review.

[d95err]

It seems unnecessary to use two separate gyrator circuits. You could use a double pole switch to swich between the two capacitors that determine the frequency. Or, even better - use a rotary multi-position switch to select between even more frequencies.

[nisios]

The thing is that i have 4 op amps so.....

anyway i done a couple of experiments and i changed the schematic already......

Now im using a movable frequency, fixed Q filter......from the geofex papers......i missed that one earlier.

Now i have one spare op amp stage.......what should i do with it....any sugestions that dont onvolve more potenciometers?

If not used is is wise to make it aground follower?

[johngreene]

The thing is that i have 4 op amps so.....

anyway i done a couple of experiments and i changed the schematic already......

Now im using a movable frequency, fixed Q filter......from the geofex papers......i missed that one earlier.

Now i have one spare op amp stage.......what should i do with it....any sugestions that dont onvolve more potenciometers?

If not used is is wise to make it aground follower?

If it was me I would use it to make a solid Vb supply.

--john

[nisios]

Im usig two 9v bateries because it improves the sound a lot.......really.

So.....is the any other application?

Isnt the gound follower exacly that?

I just seen it beeing used on a schematic but i dont undestand what it does.

Does it try to maintain 0v at all cost? But isnt groud at groud at all time? what can upset ground?

[johngreene]

Im usig two 9v bateries because it improves the sound a lot.......really.

So.....is the any other application?

Isnt the gound follower exacly that?

I just seen it beeing used on a schematic but i dont undestand what it does.

Does it try to maintain 0v at all cost? But isnt groud at groud at all time? what can upset ground?

Since your schematic only shows 1 +9V supply, I'm not sure how you are using the 2 +9V batteries (+18V or +/-9V). I don't understand what you mean by 'ground follower' either.

--john

[nisios]

well....in the breadboard i used +/-9.....i think this is the best choice ... no?
I can eliminate the voltage divider this way.......but i have one doubt......lets say one battery wears off faster than the other.......wont it distabilize the supply equilibrium?
This coulld be fixed with the 18v supply with voltage divider, but wont this raise the noise on the circuit?

Another question
Do i still need the 470k resitor to ground on the input?
Or does it raise the input impedance too much?

and another :

At full gain theres some perceptible noise....without voltage divider........is there any way i can eliminat it? Maybe with the help of the spare op amp stage?

[nisios]

Sorry for so many questions at a time 

[JHS]

A freeware program for calculating gyros called "gyrator.zip"

http://www.elitesecurity.org/t228672-Sema-ekvilajzera-pcb-molim-za-pomoc

JHS

[nisios]

Thanks....the link doesnt work from here.....but i ended up finding it on that forum.