Good morning all,

I am looking for some enlightenment on the subject circuit. I know just 
enough about it to be dangerous and not enough to understand what 
exactly it does and how to select the corner frequency of the high pass 
filter. I have not been able to obtain a copy of Wielandt's paper "Noise 
in Electronic Seismograph Systems", so if anyone has an electronic copy 
(in english) I would appreciate a copy. Short of that, can anyone 
provide an explanation of how this thing works, and what the 
alternatives to it might be.

I understand that the output of the high pass filter is fed back to the 
input amplifier and subtracted from the input signal, but doesn't the 
phase shift in the filter prevent this from working as Allan Coleman 
describes in his papers?

Thanks for any help you may provide

Dave Youden
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