If someone want to use a chopper amp there is a good circuit at
the URL below. There are two amps on this page. I have built and
currently us the amp that has the 1hz filter with no problems. 
What I like is there is no drift of the output voltage,
which mean fewer re-adjustments. I have modified the the off set
adjustment section of the circuit which makes it easier to adjust.
If you are interested in my mod please contact me.

http://www.info2000.net/~aloomis/seismom.htm

Regards,
Dewayne Hill

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