PSN-L Email List Message

Subject: Placing Geophone on Negative Feedback leg of op amp
From: "Geoffrey" gmvoeth@...........
Date: Tue, 9 Jun 2009 17:20:48 -0700

Hello Chris;

I tried the technique you suggested and
in preliminary testing I believe I received
a recent Alaska teleseismic quake of
4.1 at 38 degrees. It was deep ( 131Km )
and only barely perceptible using audacity
to hear it and Winquake to filter/integrate
the results. This is the weakest signal received
by me that I could still say it was some kind
of earth quake.

I could never say 100% it is in fact an Eq yet
the frequency range and time of arrival
( within 2 to 3 seconds of theoretical )
suggests to me it was in fact the Alaska event.
ARRIVAL TIME here: 18:46:21_2009JUN09_UTC
I was not able to use this idea before because
of drift with high gain but since using a DC
blocker (HPF) your idea has been working.

Placing the geophone between ground and the negative
input of the preamp/LPF with a 100K feedback resistor
gives about x228 of gain in the preamp for this setup.

Thanks for the recommendation.



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