Fractal Audio AMP models: your super guide to all AMP models

iaresee said:
Super forumite and beta tester @yek

There's a comprehensive PDF Guide now too, containing the contents of all threads, and more.
Click to expand...

Hi,

Thank you very much for compiling the info into a very neat and uniform format! Many thanks to Yek for and other contributors for the valuable information as well.

I would like to learn the importance of negative feedback. I noticed that this info is always present in the table at the end of each amp description. Why is it important to know if an amp has a negative feedback or none?

Thanks!
 
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Ytolyccuz said:
Hi,

Thank you very much for compiling the info into a very neat and uniform format! Many thanks to Yek for and other contributors for the valueble information as well.

I would like to learn the importance of negative feedback. I noticed that this info is always present in the table at the end of each amp description. Why is it important to know if an amp has a negative feedback or none?

Thanks!
Click to expand...
Hey! You'll probably attract more interest in your question if you start a thread specifically about this topic.
 
Ytolyccuz said:
Hi,

Thank you very much for compiling the info into a very neat and uniform format! Many thanks to Yek for and other contributors for the valuable information as well.

I would like to learn the importance of negative feedback. I noticed that this info is always present in the table at the end of each amp description. Why is it important to know if an amp has a negative feedback or none?

Thanks!
Click to expand...

Don't be afraid to use Google.

http://www.aikenamps.com/index.php/what-is-negative-feedback

One of the prominent effects of negative feedback is perceived tighter low end.
 
Ytolyccuz said:
Hi,

Thank you very much for compiling the info into a very neat and uniform format! Many thanks to Yek for and other contributors for the valuable information as well.

I would like to learn the importance of negative feedback. I noticed that this info is always present in the table at the end of each amp description. Why is it important to know if an amp has a negative feedback or none?

Thanks!
Click to expand...
You may like to read directly from Cliff:
http://forum.fractalaudio.com/threads/about-negative-feedback.79697/

Or all the tech notes from him:
http://forum.fractalaudio.com/forums/tech-notes.77/
 
barhrecords said:
One of the prominent effects of negative feedback is perceived tighter low end.
Click to expand...

Hi Barh,

Thanks for this very easy-to-understand description. This is exactly the type of explanation that I was looking for. Sorry to come out as a lazy poster... I tried looking it up but ended up more confused. Below are some excerpts from the fractal wiki:

"Negative" feedback means that a phase-inverted version of the output signal is fed back, that is, everytime the input signal is positive, the output signal is negative and vice versa. In effect this does not add to but subtract from the input signal. In other words, the overall amplification of the poweramp is decreased (hence the word "damping").

Why would some amp designer want to do that? The answer is that negative feedback also decreases nonlinearity in the poweramp. Consider what happens when the amp starts to distort. That is, the power supply isn't able to deliver the voltage which is necessary to linearly amplify a very high input voltage. The actual output is a bit lower -- and so is the signal in the feedback loop! There is less signal subtracted from the input, the overall gain is slightly higher for that input voltage. The feedback loop "linearizes" the poweramp a bit.:dizzy::dizzy::dizzy:

How negative feedback affects harmonic distortion
Reducing negative feedback increases harmonic distortion including 2nd and 3rd if operating below clipping. This is because feedback linearizes the amplifier. The Axe-Fx has a non-linear "power amp" just like a real tube amp and if you turn down the feedback (damping) then the power amp will be less linear and will therefore introduce some distortion products. The distortion products tend to be low order (2nd and 3rd).

Once you enter clipping, negative feedback can actually increase the distortion products since the onset of clipping is sharper. A power amp with no negative feedback (i.e. AC30) will produce distortion even when not clipping. However, it will go into clipping gently since the transfer function tends to be smooth. A power amp with negative feedback will produce less distortion when not clipping but will enter clipping more abruptly since the smooth curve is essentially turned into a piecewise linear function with an abrupt gain reduction at the supply rail. :dizzy::dizzy::dizzy::dizzy::dizzy:
​
I'm also very new to how amps work and the axe fx, I know I need a lot of help to ease my way into learning the wealth of information in this forum.
 
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