Q: Qualitative explanation of the high open-loop gain of a 741 op-amp using its internal circuit characteristics Here is the internal circuit of a 741 op-amp:

Using small signal analysis, I can claim the open loop voltage gain to be the product of the current gain of the transistors in the Darlington pair(Q15, Q19) and those in the input circuit emitter followers(Q1, Q2).
This should not include the output push-pull amplifier stage (Q14, Q20), as it has no voltage gain.
This can give me somewhere near the order of 10E+8, thus nearing infinity, as it should be for an ideal op-amp.  When I looked up the characteristics of the 741 op-amp, it shows an open-loop gain of around \$2 \times 10^{5}\$.
Is there any way to understand this deviation qualitatively, or does one have to do the simulations and calculations to understand in this case? Does this occur due to the frequency response of the circuit? I would like to observe this qualitatively at first, before going into the simulations and the extensive calculations, in order to carry an intuition before actually testing it out. Can someone help me out in this?

A: You have two principal gain blocks, the input differential to single-ended amplifier around Q1, and the amplifier around Q15.
Both of those amplifiers involve output loads which are ideally infinite, but whose impedance will be brought down by real transistor effects like finite output impedance of the Q4/6 current source.
What you're being asked to do is to get an understanding of how the circuit works, so that when you make the (inevitable) mistake or three doing detailed calculations, you have a better chance of debugging where you went wrong, and indeed spotting that it's wrong in the first place.
Both figures of 108 (how did you arrive at that?)(show your working and we can advise better) and 2x105 are 'big', so you could be in the right ballpark. If the difference is real transistor effects, so lower hfe and hoe than you expect, then you're there, because there are lots of them and they would all multiply up.
Don't neglect the loading that the darlington stage puts on the first stage. You need to examine this stage carefully to see what its input impedance and gain are. Don't neglect the input impedance of the output stage on its gain either.
If you could walk us through how you arrived at 108, then we could give you a better critique.
