Feedback

Hi there guys.

I have just one quick question and i hope i can get a practical aproach.

What is feedback and how can you explain this practically?

I am talking here about transistor aplifiers. Why you have to send a fraction of output signal back to input?

Thanks in advance.

An amplifier has non-linear transistors that produce distortion. If a lot of transistors are used then the gain is very high and negative feedback can be used to reduce the gain to a useable amount which also reduces the distortion.

An opamp is frequently used as an audio amp. A TL07x opamp has a typical gain without negative feedback of 3000 at 1khz. With negative feedback its distortion is only 0.003%.

Positive feedback (feedback signal in phase with the input) will cause instability and possible oscillations in the circuit.

Negative feedback (feedback signal 180 degrees out of phase with the input) will reduce the gain and distortion. Basically it reduces distortion by sort of comparing (subtracting) part of the output from the input. Any differences are distortion and the negative feedback for the distortion part is thus higher than for the non-distortion part. This reduces the distortion part at the output.