I have a circuit diagram of a detector and filter design that is to be
used with a induction coil antenna, designed to pick up ELF (under
50Hz). The circuit needs to filter out high frequency signals and
amplify the remaining low frequency. The detector part of the circuit
consists of two Op-Amps that I think are only for amplification
purposes, the filter is made of a 3 Stage (Op Amps) part and a T
network notch filter. The Circuit needs to be reverse engineered
however, I am having problems doing this, especially with the three
stage filter as it does not seem to follow any normal low pass design
standards. Can you explain the way the circuit works and show the
relevant gains and frequencies for each stage? I will e-mail you a
copy of the ciruit if you take the question. Cheers, Stimpy.

May I suggest you take your question to "Tony's Answer Forum", this is
a non-commercial site for people interested in electronics where I'm
sure you'll get some good advice for free. The URL is:
http://www.uoguelph.ca/~antoon/Forum/Forum.html
Good luck, Gwilym.

thanks very much for the advise. I've posted it on tony's answer forum
and the circuit diagram has been added as a URL link.