negative feed back is used in amp designs to decrease gain and prevent distortion.
It with clipping diodes is used in many overdrive/distortion pedals.
The clipping diodes add an artificial distortion to the signal.
Removing them increases gain, ie no negative feed back.
Placing a resister or potentiometer in the loop allows for adjustment of the feedback and gain.
Putting a capacitor in series with the pot, any thing from small value of 100 pf to a larger value like .1 uf, filters the signal being fed back creating a resonance circuit, which acts similar to a presence but controlling the gain as well.
Positive feed back, not used as much, can be used to increase gain. With a potentiometer and capacitor and a limiting resister one can create a resonance circuit that boosts the gain and changes the tone.
More gain drives amplification devices, tubes, opamps, transistors into natural saturation clipping occurs creating a more natural sounding distortion.
MM