Thank you Hydron for the comments, and I agree, but that was not my intention.

I was interested only in the rather unusual front-end section and wanted to get a feel for the three things that stood out for me in this design. Tek engineers generally do that with good reason, and I wanted to try to understand why.

First the relatively low parallel HF capacitors of 2.2pF, (only 1.1pF in total) which makes the front-end much more sensitive to parasitic or stray capacitance. In all the other designs I have found a minimum of 4pF in total, which is about a factor 4 more and so is 40x the typical 0.1pF for parasitic or stray's instead of only about 10x more.

Second, the attenuation factor due to the 4M vs 6K81, which drives the rather odd LF compensation circuit with the strange, for me at least, dual parallel trimming section with R/C networks. In simulating the circuit, I found that the value of the LF 60.5pF I arrived at is extremely sensitive (I also used MC analysis), and the whole front-end is not flat. All the other attenuation designs I looked at can be easily calculated, and when simulated are flat.

Third, the interesting circuit to adjust the CMR (2x 100K and a 25K trimmer). In all the other designs I found, the engineers use a 100-500 Ohm trimmer between ground combined with the two attenuation resistors (here the 6K81), which not only adjusts the CMR, but also the attenuation factor. I like the Tek method better, so I'll use that for my own design.

I'm looking forward to get more comments about of this interesting circuit

Enjoy!

Paul