READ THIS FOR E-SCOPE CKT
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1) OP-AMP U1 is LM 387; is a low-noise pre-amplifier.
   it uses +12v and ground. Here it is designed for a gain of 
    jsut above 500.
2)  The remaining op-amps U2,U3,U4 are 741s using +12 and -12v.

3) The second satge is a butterworth secondorder LPF,at 600Hz cutoff.

4) The name CAP in the input,is for the input condeneser microphone.
    Use sheilded wire between mic and pre-amp.