I have a QA401 and QA470 connected with 30 dB amplifier. I would like to know why in the specs of QA470 the input coupling is AC and Fc= 2 Hz for the 30dB and 10dB amplifiers.
Making some test about voltage references and RC Filters the voltage change when I connect the input of + 30 dB amplifier. I can see that the coupling is DC and not AC because with a multimeter I measure 100 Kohm all the time in every amplifiers inputs.
This condition affects all the measures for cause of the loading the circuit with 100 Kohm and changing the workind DC point of the device under test creating and unexpected behaviour and of course a bad result. I use this amplifier because the limit of DC voltage of QA401 is 5v and QA470 is 50v. Normally I’m working with 15v supply. The solution is a capacitor before the BNC input but i dislike it.
Have you got any solution, for this,
It seems a mistake, the QA470 is internally connected diferent of your specifications.
Is possible to be more length in the Title field? Sometimes this space is limited for explanation, perhaps one solution can do that this field accepts two lines of text.
Imagine this serial circuit, DC-DC converter (Out A) to a LM317 regulator (Out B) to a Sziklai noise reductor (Out C) to a load of 100 Ohm.
I would like to view in the same graph the plots of the Noise Floor with input shorted and Out A, B and C with different colors.
Now only I have one snapshot of the Noise Floor, overlay in green color and the plot of DUT in blue color, only two.
Could you implement these features for new software versions?, now I’m using the v1.917.
Any suggestion will be apreciated. Thanks in advance.