OP AMP AC Simulation

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Which very old opamp are you testing that has a gain of only 92dB and no gain above only 100kHz?
The lousy old 741 opamp was introduced 47 years ago and is a little better than that. Maybe you are testing a lousy old 709 opamp that was introduced 48 years ago.
 

You don't understand how the circuit operates.
The rolloff needs to be more than the open-loop gain at the frequency of interest so it doesn't affect the measurement (in other words you want very little feedback at the frequency of interest). That's likely in excess of -100dB for most op amps at 1Hz or below.
So an RC circuit rolloff of -16dB at 1Hz would not allow such a measurement.
 

The 1 Farad requirement in this case is to attenuate more than the open loop gain at 1Hz, thus > -130 dB attenuation @1Hz isn't overkill. But we must assume the lowest frequency flat response is the DC gain and find a good 1 Farad capacitor that has leakage >>>1M Ohm ( doesn't exist yet)

But there are more practical methods used in industry for measuring open loop gain for DC gain


and AC gain

 

Interesting discussion, but not related to the OP's question.

1. He's clearly asking about simulation, not gain measurement in real hardware.
2. He used an 1 F, not 1 µF capacitor
 

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