Added the attenuated input pin. At 1V @ 10kHz input from the sig gen, the trace of the attenuated input is a straight line. So turned the signal up to 10V.
So using a 10V signal input, after the voltage divider the input to the inverting pin is 1mv, Note: I cherry picked and did find 1% @ 999kΩ & 100Ω resistors. Not an enormous amount of gain here. In just 2kHz it loses 10k gain and as the freq continues to increase the output becomes unstable. @40kHz gain is down to ~80. I did some jury rigging and was able to get the board into my Faraday box but there was no noticeable difference. One thing I do like about opamps is their ability to filter out noise from the input signal. Also I've been meaning to ask. The 2nd opamp, I used a second TL071CP and I assume this was correct and not another model was needed?

 

Why are you measuring the open loop gain of this opamp?
When is an opamp used with an open loop?
Another graph is shown of its poor high frequency slew rate at high levels.
They are shown on the datasheet so that you can see that an opamp works poorly at high frequencies.

 

Where did you find that? I only have the TI PDF and in it is only the dB to Freq chart. Looking at both charts briefly my results are not too different. In fact my gain may be a bit higher. I'll do more charting and analysis of results tomorrow. As I said before, trust but verify and learn by doing so. Besides, I got to work on my layout and soldering skills building the test module.

 

The graph that @Audioguru again provided tracks exactly as the dB graph on the TI PDF. I added my results, and they track perfectly between 100Hz-1kHz albeit a bit lower and dropping off rapidly under and over those frequencies. So, I consider it a somewhat valid test. Now, back to the handbook!

 

TI has a new TL071 datasheet (December 2021) introducing the H version but the graph I posted is for the original version.

The frequency compensation in an opamp is done with only a single capacitor so that the phase shift is not more than 90 degrees which would cause an amplifier to oscillate or produce the instability you said occurred.

Your measurement wrongly shows a steeper high frequency loss maybe because the high frequency level is too low for you to measure. At 1kHz you measured an output of 2.3Vp-p then at 100kHz the output should be 1/100th at only 23mVp-p.