Engineering Analyzing the output impedance and open loop gain of a IC-741 Op-Amp

[PhysicsTruth]

Homework Statement

Analyze qualitatively, the output impedance and the open loop gain of a IC 741 Op-Amp from its internal circuit.

Relevant Equations

$V_{out} = A_{o} ( V_{in1} - V_{in2})$
$A_{o}$ is the open loop voltage gain.

Here is the internal circuit of the 741 Op-Amp -

Looking at the output stage, the output impedance seems to be the series combination of $25 \Omega$ and $50 \Omega$, that is $75 \Omega$. Is this a qualitative explanation enough to justify the output impedance, or am I wrong somewhere and need to take into account some other impedances as well.

Coming to the open-loop gain, the output Push-Pull amplifier has no voltage gain, only it's achieved at the Darlington pair and the initial input stage emitter followers. How do I go on to claim qualitatively that the open loop gain is significantly high, and nearing infinity?

 

[DaveE]

Looking at the output stage, the output impedance seems to be the series combination of 25Ω and 50Ω, that is 75Ω. Is this a qualitative explanation enough to justify the output impedance, or am I wrong somewhere and need to take into account some other impedances as well.

No. The output current flows either through one resistor or the other, depending on the output voltage and the way the load is connected. So it's basically 25 ohms or 50 ohms; there is no combination.

 

[PhysicsTruth]

No. The output current flows either through one resistor or the other, depending on the output voltage and the way the load is connected. So it's basically 25 ohms or 50 ohms; there is no combination.

Okay, I realize that now. Coming to the open-loop gain, I guess only the Darlington pair, and the input stage emitter followers contribute to the small signal open loop voltage gain, and that should be the product of 4 transistors' current gain, and should be around the order of 10E+8, which is nearing infinity, as it should be, for an ideal op-amp. But, on doing some more extensive search, I found that the open-loop voltage gain is around $2 \times 10^{5}$ for the 741 Op-Amp. Where am I possibly going wrong, and does this happen due to the frequency response?