Attenuating a 10V Sin wave [Circuit design]
What you've actually made between your signal line &amp; your AD8676 in the second diagram is a "pi attenuator."

While a pi attenuator could actually be used quite well in this instance, I think yours has the wrong resistor values.

Here's a link to a calculator made specifically for making impedance-matched pi attenuator circuits like that: Pi Attenuator Calculator

using that calculator, if your op-amp had an input impedance of 50ohms, the following would work:







simulate this circuit &ndash; Schematic created using CircuitLab
Since, however, the input of the OA is closer to 1Mohm than 50ohm, you'll probably want to do a little checking on "Impedance Matching Pi Networks" if you need to avoid reflections on the incoming signal cable.

EDIT

Or, if we stop over-complicating things on ourselves, using the fact that the op-amp's input can be considered infinite-impedance, compared to the 50-ohm required load, you could use this even simpler circuit:







simulate this circuit