Originally posted by Goaty
View Post
With 470nF, the corner frequency of this high-pass filter is ~34Hz, and with the 22uF (suggested by Eric) it's 0.7Hz.
While experimenting with a different design to the MPP, I encountered the same problem with less than perfect Earth field elimination (EFE), so decided to investigate further. This design was also using a high-pass filter between the preamp and the sampling integrator, with a capacitor value of 470nF, and there was a definite improvement in EFE when this capacitor was increased in value. However, there was a much greater improvement when the capacitor was shorted out, and the resistor to ground (R19 [10k] in the MPP) was removed. I'm not sure whether this is possible with the MPP, as it does not possess the ability to set the null-offset of the preamp, so maybe you can try this and report back. If increasing C12 to 22uF, or shorting C12 and removing R19 does not do the trick, then you will need to look elsewhere for the problem.
Comment