Attached is the transfer function for the bandpass filter I built for the AOSEM readout. The schematic is primitively outlined below. The corner frequencies are what they should be (HP: 100 mHz, LP: 1 kHz)

The Johnson noise for the 1 k resistor is roughly 4 nV/rt(Hz). Frank says that it doesn't make sense to use much lower than 1 k if I'm putting it into an SR785.

           10 uF                  1 k

      -------| |-------------/\/\/\/\/\/------------------

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        < |

         160 k  >        _|_  160 nF

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