From Alan:
I am attaching a calculation (as a Matlab live script and as a PDF) of the gain in dB vs. DAC voltage, to aid in creating the user’s gain control. It includes a formula which attempts to take the rounded end points into account as each of the two cascade chips runs through its gain range in sequence (the first from DAC voltages of -0.5 to +0.5 and the second from +0.5 to +1.5). As we discussed, the user should have a slider control marked in dB, along with an input box that allows typing the desired gain instead, for convenience; the slider and the input box both indicate the gain. The selected gain should be converted into the corresponding DAC voltage, from -0.65 to +1.65 V.
The chassis bypasses the amplifier if the DAC voltage is less than -1 V. There should be a bypass on/off switch that sets the DAC to something about -1.2 V (to be far from the transition). When bypassed, the path attenuates by -5.6 dB (almost a factor of 2 in voltage). When the bypass is turned off, the DAC can go to 0 V, since that gives almost the same gain, -5.2 dB. The user won’t see a big jump and can tweak from there.
