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 Prattwrote: 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 =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;"> = p> =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. = span>
=0A=0A=
=0A=0ACan y= ou explain more?
=0A=0A=0A=0A
Randy
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