This will lead to transfer functions with two 0.0723 Hz zeroes, two 3.34 Hz poles and a DC gain of 0.957, or -0.4 dB. The HF gain becomes 45.2 squared, or 2040. Two further poles are located at 15.4 kHz.

During testing we noticed that the input transimpedance amplifiers (eight AD797s), were all oscillating between 10-15 MHz with an amplitude of about 500 mVpp. Adding capacitance to the feedback network seemed to have little effect, so we swapped all of them with TLE2027. This solved the oscillation. Using 400 Ohms transimpedance, the input referred noise of a channel is about 25 pA/√Hz between 10 Hz and 10 kHz. This is maybe a factor of 2 below shot noise at high laser input power. The electronics noise is dominated by the Johnson noise of the first 4.87K resistor in the whitening stages.

The output SMA connector which was shortening the negative leg to the chassis has been removed. Instead, we drilled a new hole for an isolated TNC connector.

With the upfront whitening gain the fast monitor points now have too much gain and are saturating. We removed the gain of 50 from ERR1 and ERR2 by replacing R60 with a 4.53K (from 220K). This also removed the 2.7 kHz pole in this path. The OUTPUT channel was also modified for a flat transfer function with a fixed gain of 1. It now looks like the other two. In detail, C52 and C53 were shorted out, and R60 and R61 were changed to 4.53K (from 45.3K).