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About Negative Feedback

jefferski

Fractal Fanatic
Thanks for the advice on rather than turning up the Damping, turn down the Master. You described it perfectly - I find that sometimes the breakup on a Fender model can be a bit harsh and have gotten in the habit of compensating by turning up Damping, which does clean it up nicely but you're right - it becomes kind of sterile. Will make a note to try the Master next time.
 

reclavea

Power User
Cliff,

Thanks a bunch for your generosity and time to deliver these in depth information on the science of all this!

This surely sparks enlightenment and appreciation for those of us who crave for deeper knowledge and understanding!

Definitely MUST KNOW information when sculpting our own sound!

Kudos again ....much appreciated!



......someone should wiki!
 
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Jul

Inspired
Electronics and Electrical theory contain the most abstract concepts I've ever encountered in my life. My hat's off to all of you that get it. I remember being exposed to AC circuits in college where they presented the material in terms of " i " ...." i " being the square root of -1. Think about it. Subsequently I happened to fail that class and swore I'd never venture into that realm ever again.
 

GM Arts

Power User
Electronics and Electrical theory contain the most abstract concepts I've ever encountered in my life. My hat's off to all of you that get it. I remember being exposed to AC circuits in college where they presented the material in terms of " i " ...." i " being the square root of -1. Think about it. Subsequently I happened to fail that class and swore I'd never venture into that realm ever again.
And strangely .... the " i " you refer to is used to generate Fractal patterns! I think we've come full circle :lol
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
Electronics and Electrical theory contain the most abstract concepts I've ever encountered in my life. My hat's off to all of you that get it. I remember being exposed to AC circuits in college where they presented the material in terms of " i " ...." i " being the square root of -1. Think about it. Subsequently I happened to fail that class and swore I'd never venture into that realm ever again.
Electrical Engineers use 'j' for sqrt(-1) because we use 'i' for current.

Imaginary numbers are no big deal. It's just a convenient way to represent certain physical quantities that require two values to describe them. In electronics a sine wave is a fundamental concept since all real signals can be broken down into a sum of sine waves (Fourier theory). A sine wave has a magnitude and phase. It can also be described using a complex number which is the sum of a real value and an imaginary value. Using a complex number makes calculations easier since the mathematical rules on complex numbers are straightforward. For example if we add two sine waves of the same frequency we get a sine wave. If we try to do this using the magnitude and phase it's cumbersome, i.e. a1 * sin(wt + theta_1) + a2 * sin(wt + theta_2) = ?. With complex numbers it would simply be (a1 + jb1) + (a2 + jb2) = a1 + a2 + j(b1 + b2).
 

Sixstring

Axe-Master
Electrical Engineers use 'j' for sqrt(-1) because we use 'i' for current.

Imaginary numbers are no big deal. It's just a convenient way to represent certain physical quantities that require two values to describe them. In electronics a sine wave is a fundamental concept since all real signals can be broken down into a sum of sine waves (Fourier theory). A sine wave has a magnitude and phase. It can also be described using a complex number which is the sum of a real value and an imaginary value. Using a complex number makes calculations easier since the mathematical rules on complex numbers are straightforward. For example if we add two sine waves of the same frequency we get a sine wave. If we try to do this using the magnitude and phase it's cumbersome, i.e. a1 * sin(wt + theta_1) + a2 * sin(wt + theta_2) = ?. With complex numbers it would simply be (a1 + jb1) + (a2 + jb2) = a1 + a2 + j(b1 + b2).
Wow... I should have gone further in my electronics studies. Hey Cliff, it's really cool to see you posting more often :encouragement:, nice to know your accessible and not completely chained to your work... Thanks very much!
 

smcrosby

Power User
Electrical Engineers use 'j' for sqrt(-1) because we use 'i' for current.

Imaginary numbers are no big deal. It's just a convenient way to represent certain physical quantities that require two values to describe them. In electronics a sine wave is a fundamental concept since all real signals can be broken down into a sum of sine waves (Fourier theory). A sine wave has a magnitude and phase. It can also be described using a complex number which is the sum of a real value and an imaginary value. Using a complex number makes calculations easier since the mathematical rules on complex numbers are straightforward. For example if we add two sine waves of the same frequency we get a sine wave. If we try to do this using the magnitude and phase it's cumbersome, i.e. a1 * sin(wt + theta_1) + a2 * sin(wt + theta_2) = ?. With complex numbers it would simply be (a1 + jb1) + (a2 + jb2) = a1 + a2 + j(b1 + b2).
:lol now you are taking me back to my freshman E.E. classes at Rutgers. :)
 

DukeOfPrunes

Experienced
Electrical Engineers use 'j' for sqrt(-1) because we use 'i' for current.

Imaginary numbers are no big deal. It's just a convenient way to represent certain physical quantities that require two values to describe them. In electronics a sine wave is a fundamental concept since all real signals can be broken down into a sum of sine waves (Fourier theory). A sine wave has a magnitude and phase. It can also be described using a complex number which is the sum of a real value and an imaginary value. Using a complex number makes calculations easier since the mathematical rules on complex numbers are straightforward. For example if we add two sine waves of the same frequency we get a sine wave. If we try to do this using the magnitude and phase it's cumbersome, i.e. a1 * sin(wt + theta_1) + a2 * sin(wt + theta_2) = ?. With complex numbers it would simply be (a1 + jb1) + (a2 + jb2) = a1 + a2 + j(b1 + b2).
Cliff, do you frequently encounter zeroes and poles in these types of computations and if so, does it have any effect of the overall stability of the system.

Really just curiosity on my part, since I encountered these in my one and only complex analysis course 30 yrs ago...

Cheers and hope the knee will be back online soon...gotta log that Carr amp to the MIMIC shop...
 

Stadanko

Inspired
Hi Cliff,

I have forgotten a lot from my calculus and linear algebra days. My question is on linearity. I always seem to get it in my head that the term "linear" ends up meaning that we are dealing with non exponential equations. So x^x would not exist in a linear equation. Is linearity more complex than that? If so I certainly don't in expect you to teach a class here! Most people in non mathematical world, terms think of linear as a straight line or a rate of change which is simple and straight forward. Like if events are in chronological order then we say they are linear in nature. I know if I could clarify linearity in relation to this topic, I would be well "clued in" a bit more..:D

Thanks
Frank
 

shatteredsquare

Fractal Fanatic
since the Dual Rec Modern mode actual amp has no negative feedback, I've read that the presence control in modern mode is actually part of the preamp, like a separate top end filter after the preamp. Is the model in the Axe Fx the same as that? If you turn the recto modern Sag to zero and the model presence control turns to a hi cut, is it the same filter?

I read on the firmware notes that the recto models are now an "exact digital recreation" so i would assume so, but I also read in a few firmwares before that some amps got "corrections" to various parameters or component values that were either off, or needed to be updated.

but i also read that you got some crazy different values from a bunch of different Recto heads, some with different pot values and tapers and such. do you know what year the modeled rectos 1 and 2 are in the latest FW?

it's good to know all these details about how the controls interact based on the amp design, it's much easier to dial in tones than just blind experimentation. without knowing it's like trying to track vocals not knowing what threshold attack release and ratio do. if you know it's like playing with legos. just build stuff.
 

Mike Ruby

New Member
Very informative post! It makes me feel like I'm taking the right path for our project with the AXlll. Am I wrong to assume that negative feedback produces odd order harmonic distortion versus even order distortion in most circuits?
 

guitarfreak365

Inspired
I got turned onto this thread after I started turning up Negative Feedback on Class A amps. Specifically the FAS CLASS A amp. I wan't sure what i was doing. Now I know more of what I'm doing haha Does anyone else do this?
 

Rex

Legend!
I thought the thing about class A amps like Vox was not to have any negative feedback :rolleyes:
Class A operation and negative feedback are two different things. The Vox is Class A (more or less), and it has no negative feedback. In the Axe-Fx, you can change that in any way that suits your ears. :)
 

OddManOut

Inspired
I’ve just reread Cliffs tech note on negative feedback after having read it when originally written. As an electrical engineer with years of designing op amps I can say that he is spot on. Articles like this help us to recognize what a unique talent and expertise Cliff possesses - he knows the theory, he has deep experience in the design and modification of tube and other analog electronics and he’s been able to translate all of this into the digital signal processing realm in such an accessible and usable way. I continue to be impressed be Mr Chases accomplishments and am happy to be along for the ride! And I know this list of accomplishments only just scratches the surface. The electric car folks have Elon Musk but we have one better - Cliff Chase! He goes to 11.
 

2112

Fractal Fanatic
I’ve just reread Cliffs tech note on negative feedback after having read it when originally written. As an electrical engineer with years of designing op amps I can say that he is spot on. Articles like this help us to recognize what a unique talent and expertise Cliff possesses - he knows the theory, he has deep experience in the design and modification of tube and other analog electronics and he’s been able to translate all of this into the digital signal processing realm in such an accessible and usable way. I continue to be impressed be Mr Chases accomplishments and am happy to be along for the ride! And I know this list of accomplishments only just scratches the surface. The electric car folks have Elon Musk but we have one better - Cliff Chase! He goes to 11.
Imagine a Tesla with a built in Axe-Fx (or should I sa an Axe-Fx with a built in Tesla :p).
 
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