Revenge for an earlier incident?Unless I take a scalpel to someone.... ANY Volunteers??
JimB
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Revenge for an earlier incident?Unless I take a scalpel to someone.... ANY Volunteers??
In that case I would suggest a signal chain made up of 1) an instrumentation amplifier to get noise cancellation and common-mode rejection; 2) an active (i.e., buffered) notch filter to reject the 50 Hz mains fundamental frequency; 3) a multi-pole active low-pass Butterworth or Chebyshev filter to get rid of high-frequency noise, including mains frequency harmonics; and 4) a final amplifier stage to boost the signal level up to a usable level.Apart from the heart most of the other frequencies I am likely to get hold of are all under 40Hz.
Search for EKG and EEG circuits and you'll get lotsa examples from hobby to pro. The good ones rely on a well designed instrumentation or differential amp front end for most of the noise rejection, but some have lowpass or notch filters downstream. All filters introduce phase distortions that alter the waveshape of the signal of interest, but the frequencies of interest are so low that they are a couple of octaves away from the corner frequencies. AG is right, the line-induced noise has harmonics, but those frequencies are even farther away and can be handled by a gentle lowpass.
ak