Feedback can be a real blessing or, in some cases, a curse.
Take for example helpful feedback: gently pointing out what someone's saying or doing isn't working well.
The recipient feels better.
But then there's hurtful feedback: pointing out one's frailties or focusing on their weakness.
The recipient feels worse.
In audio, hurtful feedback is called positive feedback. You hear it as a squeal or a loud whistle when someone gets a live microphone too close to a loudspeaker.
In an audio circuit we use what's known as negative feedback. Though it sounds like it shouldn't be a good thing, negative feedback is one of the essential tools we designers have at our disposal. We take the output of an amplifier and feed it back into the amp's input. There, the two signals are compared and corrections applied so that the output more closely matches the input.
Like any corrective action, we're always better off with getting the base circuit working as well as possible before adding any kind of feedback. Which is why we always strive to design our circuitry to work without feedback—a condition known as open loop (the "loop" refers to this output to input loop).
Get the open loop response and distortion perfected and then the addition of a bit of negative feedback is like icing on a cake.
