In a message dated 25/03/2006, davenn@............... writes:

Bi-FET Op-Amps     ....  eg  the  OPA 027   and  similar 
series,  rather 741   etc  type



Hi Dave,
 
    Google can't find an OPA027 ! and neither can I  !!
    OPA27 are very low noise, but they are not Bi-FET  The later types are 
OPA227 LT1007 etc
    In general, FET opamps have a much higher voltage  noise than ordinary 
transistor types. I would not use one by choice in a  geophone or a coil sensor 
circuit. Some of the less expensive / older types  suffer from step noise - 
transient level or pulsed shifts. 
 
    When you connect up a geophone, you need to  wire the metal case to the 
earth / shield line.
 
    Regards,
 
    Chris Chapman






In a message dated 25/03/2006, davenn@............... writes:
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  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
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  Bi-FET Op-Amps     ....  eg  the  OPA 027&nb=
sp;=20
  and  similar 
series,  rather 741   etc=20
type


Hi Dave,
 
    Google can't find an OPA027 ! and neither can I=
=20
!!
    OPA27 are very low noise, but they are not Bi-F=
ET=20
The later types are OPA227 LT1007 etc
    In general, FET opamps have a much higher volta=
ge=20
noise than ordinary transistor types. I would not use one by choice in=20=
a=20
geophone or a coil sensor circuit. Some of the less expensive / older types=20
suffer from step noise - transient level or pulsed shifts. 
 
    When you connect up a geophone, you need t=
o=20
wire the metal case to the earth / shield line.
 
    Regards,
 
    Chris Chapman