Circuits for magnetic pickups

[Sandy]

Tim and others...

I was thinking much of the same idea, but was afraid that it was way too
simple. I guess that I have to go out and get a sensor, and a wheel on a car
and see how bad the noise really is. I'm guessing that it is really bad in
some cases, but if I can rid my design of the lm1815, that would be very
good. The circuit that you used on the Direct Ignition looked good, but
again looked like it would be susceptible to noise. 

Do I need to ground the - on the sensor at all? If I do, don't I lose any of
the balanced input benefits that I'm trying to get? If I grounded the (-) at
the opamp, I would guess that I would lose ALL of the benefits of the
balanced inputs.

Also I messed around with some input voltage limiting, and found that zeners
won't work, as they are too slow. I think however, that the TVS's will work
like a champ, with only a few ns to clamp.
     
     |----------------*---------()()()-------*---*------>>> OpAmp +
     |                |                      |   /
  [pickup]          [TVS]       Inductors    |   \ Gain   
     |                |                      |   /
     |----------------*---------()()()---*---|---*------>>> OpAmp -
                                         |   |
                                        --- --- 
                                        --- --- Small Caps
                                         |   |
                                         --|--
                                          GND         

This is what I was thinking, with some hysteresis on the opamp side, should
do the trick, but again this is just a guess. What do you think, and what
problems will be caused by not have a GND in the pickup side?

More food for thought ;)

Sandy