In the beginning let us confine our study on the simplest op amp circuit, which is an inverting op amp amplifier with resistive feed back.The phase shift of such amplifiers has single pole with a phase shift of -45 degrees at the - 3dB point. So in order to limit the phase shift you have to operate your amplifier in the region of the flat frequency response.

The gain can be expressed by A= A0/ (1+ jw/wc),

Where Ao is the gain at zero frequency, w is the frequency of the applied signal and wc is the cut off frequency. The phase of the gain A, phi= - tan^-1 w/wc, for w/wc=1, phi will be -45, phase lag by 45 degrees.

If we want to limit the phase delay of the amplifier to a specific value say phil: phi limit, then as phil is very small, one can approximate the phse relation ship as:

phil= - wl/wc,

Then one can gat wl= phil x wc, and fl= phil fc

fl will be the maximum input frequency, phil is the allowed phas delay, and fc is the required cut off frequency of the amplifier.  If phil= 5 degrees= .0 8726 rad, fl= 10 kHz,

Then fc= 114.6 kHz.

This example shows how far cut off frequency is much greater than the audio signal frequency. 

The question now what is the required gain of the amplifier A0 of the amplifier,

Say A0=10,

Then the minimum required gain bandwidth product of the op amp FT= greater than 114.6x10= 1146 kHz= 1.1 Mhz.So, the op amp 741 can just provide the required function with upper bound given above, that the gain of the amplifier must not be greater than 10.

Till now it is okay? not just so, because the amplifier has this bandwidth for small signals in the millivolt range. As at large signal the op amp speed is limited by its slow rate.  Since your signal is large then you have to use op amps with very high slew rate dV/dt, 

For a sinusoidal wave with  max dV/dt= Vsm wl= 1Vx 2 pi 114.6 k=720 k V/s, So you an amplifier with a slew rate not less than 1 V/us if your amplitude is limited to 1V.  If you want to amplify signals with higher amplitude you have to scale your slew rate.

Please you can build your circuit on the light of my analysis in this post. You problem will be solved.

Best wishes

Thanks a lot for you detailed answer, I appreciate a lot.

I will go to the lab to study all this and update.

Have a nice day!

There are always problems with the phase. I recommend using the Bessel approximation for filters.

I recommend www.linkwitzlab.com

great! I have a lot to learn and test now. Thanks a lot for your answers :D

Pablo,

I do not want to bother you, but in my opinion the phase management in analog circuits normally targets phase linearity with frequency. Since if the phase is linear with frequency, there will be no phase distortion and the group delay time will be constant leading to preservation of the wave forms. This solution is introduced by Josef as he proposed the use of Bessel filters.

Even if analog circuits do not have phase - frequency linearity one can use phase equalizers to linearise the phase.

One the other side, if one makes the phase always small at all operating frequencies the group delay variations will be also small. A theoretical case is one makes the phase equals to zero at all frequencies, then there will be no phase distortion. This cost of keeping the phase very small may be high. 

So, i would like that you review the requirements and specifications on your circuits.

Best wishes

Abdelhalim:

Since I´m still studying electric engineering  your experience is very valuable to me, it doesn´t bother at all. It has been a great guide for my research. Thanks a lot for your time.

About the device, my professor required to make phase close to zero as much as possible. I tried to solve that but soon I noticed I didn´t have the knoledge so I researchd info and took it to lab´s team  to receive feedback. My professor´s backgrund is physis so maybe this will definitely help improving the project.

Tanks a lot once again for your advice.

Pablo,

Congratulations, you have already made a fundamental observation :

There is a difference between Simulations and Real-World ! 

(1) You can achieve  "Zero phase analog crossover"  

only in the Ideal-Linear-Calculation-Process of Spice .  

 (2) Any use of Real-World OpAmps will involve phase distortion,   

because the Real-World is basically Non-Linear. 

I have never been able to "fix" the problems generated by Spice, 

and have been heavily "tutored"

(by several talented engineers here on RGN)  

to see the difference between Simulations and Real-World.   

Net result,   

(1) I use the Linear Spice heavily,

(2) then do real-world compensation on my real-world prototypes,  

in order to bring Spice results into line with non-Linear real-world limits. 

Your "question" has brought up some interesting considerations. 

It is very easy to miss the distinction between 

(a)  Non-Linear world,

(b) Linear-Equation-Calculation-Process Spice. 

In my opinion,

Theory can be perfect.

Spice is a Linear-Ideal-Calculation-Process ,

and can seem perfect,  

in as far as the device models are partially perfect. 

I think Dr. Zekry cautions against trying for a "perfect" real-world. 

You should read again Dr. Zekry's posting. 

Buena Suerte !

http://www.geocities.ws/glene77is/

Adbelhalim I have read again your posts but didn´t understand this 

"Please you can build your circuit on the light of my analysis in this post. You problem will be solved."

You want me to update the circuit I made? Please let me know. Thanks!

See bottom section heading "3-Way Active Crossover with Linear-Phase Response" linked from this webpage:

To do analogue filters one has to add all-pass sections to compensate for phase.

It gets complicated very quickly :)

http://www.karma-audio.dk/Linear%20phase%20crossovers.html

Pablo, i mean you have to build your circuits on clear concepts to satisfy the requirements and specifications of your system. In my first post i developed the concept how to build amplifiers with their phase smaller than specific value.

Best wishes

Bohn, "A Fourth-Order State Variable Filter for Linkwitz-Riley Active Crossover Designs", 74th Convention of Audio Engineering Society, Oct. 1983.

.

Pablo:

.

You have received a lot of feedback on

this matter so I will not overburden you

with more poles and zeros. But there's

something you originally mentioned in

your description of the problem, which

is that you have tried using some very

ancient op amps.

.

These are terrible for audio. I can help

you with some modern parts - from my

own private stock - but first, you'll need

to send me clear pictures of the actual

circuit schematics in order to make an

optimal choice. I might have trouble in

mailing to you.

.

Barrie

.

Barrie, 

Thank you for "date" of 5532 and 741.    

Have always thought that it was "just yesterday",  

however,  truth is , 

1979 is near "beginning of time" for compensated OpAmps

... indeed. 

Yes, you and ADI do have marvelous OpAmp chips. 

I still work with 1985 chips  only  

(1) because my defined phase error tolerance is great,

(2) because I cannot "hear" the difference . 

I still think that the Real World rules over modern OPA chips

and talented engineers will forever find employment

developing OpAmp chips that function at higher GigaHz range

and lower Noise range.  

Pablo, 

If you want a " achieve zero phase (or close to it)"  Filter Effect  

then you will have Zero Filter "Q" Effect ( or close to it).     

Zero "Q"  would be a useless effect, for a "cross-over" circuit. 

Surely, you have realized that a Bessel filter is an "Analog Filter", 

and that all analog filters involve phase distortions.  

If you want a filter effect,

then you also produce a phase-distortion effect. 

The problems you have discovered are

with understanding the Analog Filter Concepts,

and not so much with opamp devices.  

You might do well to specify exactly

just how much phase distortion is acceptable.  

ie, IF Q=1 is acceptable, then design for Bessel with Q=1, 

and THEN you will find that there is very little filter effect. 

You might do well to begin designing specific Schematics,

and begin defining your real-world criteria.      

Summary: 

As it stands, Pablo may be asking for

Too much Sugar for a Nickel. 

Buena Suerte en la projecta, 

Dear Glenn, and everyone giving information: 

I have been carefully collecting and reading all of the info, thanks A LOT for that. I already learned I know very little about this so I´m reading everything you sent me in order to make better questions. Also contacted a friend here in Chile for this and my other project (audio preamp) and gave some information about choosing OPAMPS.

About the device, I already read about Bessel filters and some others and I can get now that it will be hard to get a nice phase answer. We are on vacations now, so my plan now is to meet my professor with a summary of all this next week showing him the issues and find out how can we deal with that in the project´s context.

Once again, thank you all, I was very complicated looking for info and now i fell like I have a thousand more great teachers! Very exciting!

Pablo,

Hope you have returned from your vacation , pasa quatro mes,

and are ready to "think"

about the Real Analog World que no es lineal.

.

I would like to see your preliminary schematic.

.

I have this comment about the way you are thinking :

* Real Analog World is Non-Linear .

* Simulations use Linear Equations

to analyse the Non-Linear Real World.

* Real Analog World OpAmp circuits follow laws of Physics.

* Simulator OpAmp circuits follow laws of Linear Equations.

Therefore, the two world views will never meet at "zero".

.

In your language it reads something like this:

* Real Analog World no es lineal.

* Las simulaciones usan ecuaciones lineales

para analizar el mundo real que no es lineal.

* Los circuitos Real Analog World OpAmp siguen las leyes de la Física.

* Los circuitos OpAmp del simulador siguen las leyes

de las ecuaciones lineales.

*** por lo tanto,

Los dos puntos de vista del mundo nunca se encontrarán en "cero".

.

I would like to see your preliminary schematic.

.

Pablo, I hope that helps you think !

www.GeoCities.WS/glene77is is my website

with many developed analog audio filter projects.

Glen

Thanks a lot for the info. I noticed I should choose a professional software and understand how to deal with its models before working on them.

Thanks a lot!