[sdiy] How to explain how negative feedback lowers noise?

[Richie Burnett]

Negative feedback reduces noise (and DC drift, and distortion,) that occur 
inside the feedback loop because all of these things represent sources of 
error at the output that are inverted and fed back in order to reduce the 
error.  All of these things happen in an audio amplifier.  The one that it 
harder to explain is why negative feedback increases bandwidth ;-)

Negative feedback doesn't remove things like noise or distortion present at 
the input because these aren't error as far as the control system is 
concerned.  So if the set-point input is noisy the control system will try 
it's best to get the output to follow it faithfully, noise and all.

-Richie, 


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