PSN-L Email List Message

Subject: Re: PreAmplifier Design for HS-10 1Hz geophone
From: "Geoff" gmvoeth@...........
Date: Sat, 11 Aug 2007 16:18:33 -0700

I fully disagree with you based upon personal experiences.
If I use this circuit it is the only one that will
work for me but I will also try adding the additional
cap you talk about.
There seems to be a 180 deg phase shift occuring at
all freqs above some cutoff
that is applied to the plus terminal the first 90
coming from the feedback and the second 90
coming from the plus minus cap.
It works very well in my place here but i got some
12800 volt power wires only 60 feet away
and i think they may be the sources of my troubles.
The neg lead of the opamp want to be non-changing
effectively creating a phantom ground it is the positive
changes above some cutoff that are being cancelled.
This type of unheard of noise filter seems good up to
very high freqs within the limits of the op amp.

I bet if the caps were big enough you would just have almost DC.

It is funny to realize the distance between one and infinity
and one and zero are essentially the very same thing
when looking at inverses.

I need this circuit.


----- Original Message ----- 
Sent: Saturday, August 11, 2007 11:59 AM
Subject: Re: PreAmplifier Design for HS-10 1Hz geophone

> In a message dated 2007/08/11, gmvoeth@........... writes:
>> Comments welcome as well as improvements.
> Hi Geoff,
>      The 400 Ohm HS-10 requires a 2050 Ohms damping resistor and you have 2 
> K Ohms. 
>       You need a second 0.33 mu F capacitor across the 100 K resistor to 
> Earth to balance the circuit. The 0.33 mu F across the input terminals is not 
> doing anything!
>       Regards,
>       Chris Chapman   

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