Most of you know that incorporation of negative feedback within amplifier is one of major considerations when designing a hi-fi amplifier. Till now, I have only dealt with differential transistor pair as input stage of amplifier and "eliminator" of distortions fed back from output of an amplifier. Although, I'm not quite sure if all kinds of distortions get eliminated by it (when compared to the original signal brought to the input of amplifier).

This circuit (proposed and made by user G36) has distorted signal, which is being delivered to voltage-amplification stage and after that it gets corrected to original (sine wave) signal being brought to the input of amplifier. It gets corrected by the differential transistor pair stage. (not shown here but: input of amplifier is at Q1 via capacitor and the output is taken from the collector of Q4).

[![enter image description here](https://i.stack.imgur.com/X5anIl.png)](https://i.stack.imgur.com/X5anIl.png)

Only problem here is that, when the distorted signal gets distorted enough, the output signal is being clipped. When input signal amplitude is low enough the signal at the base of Q4 is distorted (spiky signal), while the output at the collector of being corrected to sine wave (note that both channels weren't set to same voltage scale).

[![enter image description here](https://i.stack.imgur.com/ED9yI.jpg)](https://i.stack.imgur.com/ED9yI.jpg)

When the input amplitude was increased progressively, those spikes were higher and higher at the same time, but the higher they were, the negative half-waves were also progressively being clipped. I added potentiometer instead of RF2 to control the portion of NFB being fed to the base of Q2 but that didn't help either.

So that left me wondering for bit, and now it seems to me that all of that distortion cannot be eliminated (or corrected) after all.

I somehow didn't manage to design a differential transistor pair amplifier myself, but maybe with your help you can help me get closer to fully understand it and make one myself that would work like it should.