Originally Posted by jackinnj
Gonna try outboarding this for the HP3577 and Bode100
Allow me to give you a simple tip.
With 50 Ohm for R19, the equivalent input noise at R19 for a 10Hz filter @3Khz and with the OPA2604 will be 38nV.
For a SNR of 35dB to give an accurate measuring result, the Signal will then have to be 2.1uV at R19. With this 50 Ohm resistor, voltage over the Cart will then be 400uV.
When replacing R19 by a 5K resistor, equivalent noise wil be 46nV with a 10Hz filter. For the same 35dB SNR you will need 2.6uV signal at this spot.
However signal over the cart will now be 5 uV, or 80 times lower as with the 50 Ohm resistor.
Your 3577 will calculate a wrong Inductance for the coil, that only has to be corrrected with a factor 100.