hi,
This shows the NPN and PNP load drive Emitter currents, they are not being equally driven.

E

Why is that !
Darlington that i studied was quite straight forward. But practically it's taking loops...

 

I do not know why you have a 20mA current generator at the input of the opamp and why the opamp has a voltage gain of 44.7 times. Why is R4 only 10 ohms?
Why don't you use power darlington transistors (TIP120 and TIP125)?
The darlington emitter-followers have some voltage loss (as you measured) and produce some distortion so why isn't the negative feedback from their output?

The opamp is not turning on the darlingtons, R2 and R6 are putting some current into the diodes and the remaining current is in the bases of the darlingtons to try turning them on, maybe making the unbalance.

 

I do not know why you have a 20mA current generator at the input of the opamp and why the opamp has a voltage gain of 44.7 times. Why is R4 only 10 ohms?
Why don't you use power darlington transistors (TIP120 and TIP125)?
The darlington emitter-followers have some voltage loss (as you measured) and produce some distortion so why isn't the negative feedback from their output?

The opamp is not turning on the darlingtons, R2 and R6 are putting some current into the diodes and the remaining current is in the bases of the darlingtons to try turning them on, maybe making the unbalance.

Hi,

Using LM741 non-inverting and AB power amplifier (from TIP31, TIP32).
My frequency response at 4ohm 10Watt speaker shows this :

is that ok ?

 

The 741 opamp was introduced to the world 52 years ago. The datasheet of the uA741 shows its slew rate has trouble above 9kHz but audio goes as high as 20kHz. Your simulation shows the output dropping above 6.5kHz. Modern audio opamps work perfectly up to 100kHz.
Its "typical" output current is 25mA but its minimum is only 5mA.

TIP31 and TIP32 transistors have a "typical" current gain of 30 at 2.5A peak (10W into 4 ohms) but the minimum current gain is only about 15 so the peak opamp output current must be 2.25A/15= 150mA.

Your simulation software does not know these important things.