If you are going the vibration route I suggest starting with the following circuit.
This is an extremely high gain version that you probably wont need.
You can try to power the circuit by taking advantage of the sound card's supplied biasing voltage with option A. I've never tried this though.
If the gain is too high you may have to implement a voltage divider at the output with optional capacitor B. This makes for a handy filter circuit
You can try substituting the op amp with another type but the 5532 has really good low noise performance in this application.
Here are some pics of the coil components.
The magnet mounted as it would be to the bottom of the experiment.
Cutting out the top and bottom coil forms from Styrofoam backing board.
Using a drill bit, paper and tape for the inside diameter of the coil form.
Making the inside diameters of the top and bottom coil forms the right size (a tight fit on the paper tube).
The finished coil form. I like to drip a lot of 5 minute epoxy into the form when I wrap the wire into it so that it creates a solid coil block that
holds the form together too. This way I can rip all of the paper out of the form when it sets, and if I've chosen the right drill bit size it produces
the smallest possible air gap between the coil and the magnet.
Wrapping the coil
The experiment upside-down, showing where the coil would be glued (or two way taped) to the bottom making sure there is an air gap all the way around
the magnet/nuts. The foam board is the same thickness as the nuts so the coil is suspended at the same height as the magnet.
Make sure your nuts and bolt are stainless steel so they do not dampen the magnetic field.
If you are using this on anything besides a low carbon (regular) steel plate I suggest shielding the coil assembly in a low carbon steel cup of some
kind to avoid interference (hum) from nearby mains fields. Test the type of steel used as a shield to make sure a magnet is drawn to it strongly.
Tighten the magnet retainer nuts only hand tight (this is why there are two). The magnet is too brittle to tighten against with a wrench (spanner)
edit on 5-12-2014 by CraftBuilder because: I can't write a single sentance without a typo.