Understanding analog signal levels - RMS, P-P, SE, and Balanced

You missed one:

Switch 2 and 3 closed: Rin = 4k99 || 2k49 || 1k24 = 1000 * 1/((1/4.99)+(1/2.49)+(1/1.24)) = 0k71

Gain (lin) = 2.49/Rin, so...

Switch 2 and 3 closed: 2k49/0k71 = 3.51x -> 10.9 dB

Looks good otherwise. I'd double-check stability at the various gain settings, especially -6 dB and around +10 dB. Just feed the circuit a 10 kHz square wave and look at the ringing, if there is any. This can be done pretty easily in the simulator and the OPA1632 model should be plenty good for this.

Tom
 
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