PSN-L Email List Message

Subject: Re: Seismic Pre-Amp
From: Pete Rowe ptrowe@.........
Date: Thu, 16 Dec 2010 15:23:36 -0800 (PST)


Hi Randy
My original schematic had no resistance=A0 in series with the coil. I have=
=A0 no resistance in my setup. However, you could make a case for some seri=
es resistance. (maybe 1k) Since the coil is connected directly to the high =
impedance, non-inverting input of the op amp, you could move the coil fast =
enough by hand to=A0 generate a voltage high enough to blow out the op amp.=
 If you want to make it more tolerant of high input voltage, go ahead and p=
ut some series resistance in. No need for resistance in both coil leads.

Pete

--- On Thu, 12/16/10, Randall Pratt  wrote:

From: Randall Pratt 
Subject: Seismic Pre-Amp
To: psnlist@..............
Date: Thursday, December 16, 2010, 1:21 PM

=0A=0A=0A =0A =0A=0A=0A=0A=0A=0A=0A =A0 =0A=0APete, =0A=0A =A0 =0A=0AI have=
 used your design for about 10 years primarily with=0Afairly low coil resis=
tance.=A0 I see matching resistors were specified as=0Aabout 5.1 K on each =
end of the 7 to 21 K coil but I have used coils of less=0Athan 1 K and anyw=
here from no resistors to 10K on each end.=A0=A0 What I=0Ahave noted most i=
s a slight reduction in output and maybe some less noise with=0Asome resist=
ance included.=A0 I do not use a damping resistor because a large=0Amass is=
 simply not possible to damp from the coil output with my magnets. =0A=0A =
=A0 =0A=0ANot to be confused with damping resistance, I have also=0Awondere=
d how to determine the value for the matching resistors between the coil=0A=
and the op amp inputs.=A0  =0A=0A =A0 =0A=0ACan you explain more? =0A=0A =
Hi Randy
My original schematic had no resi= stance  in series with the coil. I have  no resistance in my setu= p. However, you could make a case for some series resistance. (maybe 1k) Si= nce the coil is connected directly to the high impedance, non-inverting inp= ut of the op amp, you could move the coil fast enough by hand to  gene= rate a voltage high enough to blow out the op amp. If you want to make it m= ore tolerant of high input voltage, go ahead and put some series resistance= in. No need for resistance in both coil leads.

Pete

--- On <= b>Thu, 12/16/10, Randall Pratt <rpratt@.............> wrot= e:

From: Randall Pratt <rpratt@.......... ..net>
Subject: Seismic Pre-Amp
To: psnlist@..............
Date: Thursday, December 16, 2010, 1:21 PM

=0A= =0A=0A =0A =0A=0A=0A
=0A=0A  

=0A=0A=

Pete,

=0A=0A=

 

=0A= =0A

I have used your design for= about 10 years primarily with=0Afairly low coil resistance.  I see ma= tching resistors were specified as=0Aabout 5.1 K on each end of the 7 to 21= K coil but I have used coils of less=0Athan 1 K and anywhere from no resis= tors to 10K on each end.   What I=0Ahave noted most is a slight r= eduction in output and maybe some less noise with=0Asome resistance include= d.  I do not use a damping resistor because a large=0Amass is simply n= ot possible to damp from the coil output with my magnets.

= =0A=0A

<= span style=3D"font-size: 10pt; font-family: Arial;">   =0A=0A

Not to be confused wi= th damping resistance, I have also=0Awondered how to determine the value fo= r the matching resistors between the coil=0Aand the op amp inputs. 

=0A=0A

 =

=0A=0A

Can y= ou explain more?

=0A=0A

 

=0A=0A

Randy

=0A=0A
=0A=0A =0A=0A

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