Request for help with front end filter design, VLF reciever design help

[philwinder]

Hi, im designing an electrostatic reciever that works from approx. 0.1 - 15 Hz but im obviously getting loads of mains noise.
I have some simple active filters after the initial gain stages, but is there a way to filter the noise before the initial gain stage?
Normally this should be ok, but heres the snag: the receiver has to have a very high input impedance (trying to read fA) and the only way i can figure out how to do this is for the filter NOT to have a connection to ground, i.e. all the resistances/impedances add up in series and do not affect the overall Tohm input impedances. Is there a passive filter out there that does not need a ground connection?
It can either be a 50Hz notch, or a 20Hz low pass.

Many thanks,

Phil Winder

[CoulombMagician]

Look up lattice networks.

[philwinder]

Hi CoulombMagician,
I had a google for lattice networks, but the only references to them where about network structures, not filters. Care to elaborate?

Thanks,

Phil Winder