This is the circuit I made:
This simple circuit incorporates differential stage – VA (Voltage-amplification) stage – OPS (Output Power Stage). Open loop gain is high, closed loop gain is approx. the value of 10. Miller effect of VA stage is compensated via Cc, which makes local feedback. Q4 is used for biasing of the OPS – when Vce = 2.4V, the current through Q6 and Q8 should be approx. 10 mA and the current through Q5 and Q7 should be approx. C1 is used for AC to bypass Q4 to be fed into base of Q7. 1 mA. Global NFB (Negative Feedback) is taken from the output and brought back to the non-inverting input of differential stage. I was first aiming for this amplifier to be loaded by 8 Ohm speaker but then changed my mind to 100 Ohm load, since there would be too high voltage gain drop (the current through last stage should be higher in my opinion).
The current through Q3 and Q4 is approx. 10 mA, while collector currents through Q1 and Q2 are approx. 1 mA
Unloaded amplifier behaves as expected, but loaded amplifier has great amount of distortion in between its output signal. I cannot figure it out what is so wrong with this amplifier to produce such high amounts of distortion on the output.
This is the signal of unloaded amplifier versus loaded amplifier (5V per division):
What is wrong here stays a mystery for me but maybe you can figure it out.