Component List
IC 1, IC 2, IC 3 & IC 5 ..... LT1007 Linear Technologies
IC 4, IC 6, IC 7, IC 8, IC 9, IC 10 & IC 11 ..... NTE857M NTE Electronics Inc.
Note: The original design used the following device numbers instead of the NTE857M. I substituted using the 857M as it is readily available locally off the self.
IC 5 ..... OP27, IC 6 .....TL072, IC 7.....TL072, IC 8 ..... TL081, IC 9 ..... TL072, IC 10 ..... TL072 & IC 11 ..... TL081.
Resistors are 1/4 watt
R 1 & R 7 ..... 100 K
R2 ..... 3.9 K
R5, R6, R12, R13, R14, R15, R21, R22, R28, R29, R34, R35, R40, R41, R46, R47, R52, R53, R58, R59, R64 & R65 ..... 100 Ohm.
Note: The 100 Ohm resistors listed above are for decoupling devices from the rail supply.
R3 ..... 200K Linear Taper Trim Pot ..... Circuit board mount.
R8, R9, R10 & R11 ..... 560 K for 60 Hz. Notch Filter. Use 680 K for 50 Hz.
R 16 ..... 100 K Linear Taper Trim Pot. Notch filter adjust. Circuit board mount.
R4 & R27 ..... 10 K Linear Taper Trim Pots. Circuit board mount. Note: These two pots are used for DC null adjustment. They are an option but it's advisable to incorporate them into the circuit where large changes in temperature occurs. They are not used by me and I have not observed any degradation in performance.
R17, R18, R30, R31, R36, R37, R42, R43, R48, R49, R54, R55, R60 & R61 ..... 7.5 K
R19, R32, R38, R44, R50, R56 & R62 ..... 39 K.
R23 & R25 ..... 10 K. Note: R24 was deleted and therefore does not exist in the list.
R26 ..... 220 K.
R33, R20 & R51 ..... 2.2 K.
R39 & R57 ..... 18 K.
R45 ..... 51 K.
R63 ..... 50 K Linear Taper Trim Pot. Circuit board mount. Note: R63 may be a fixed resistor but I found it necessary to make it adjustable to aid in matching my laptop mic. input impedance.
Capacitors
C1 & C2 ..... .001 UF Multi Layer Ceramic.
C3, C4, C9, C10, C11, C12, C15, C16, C18, C19, C22, C23, C26, C27, C30, C31, C34, C35, C38, C39, C42 & C43 ..... 2.2 UF Tantalum. Note: Do not use electrolytic as a substitute. I have found tantalums superior. These capacitors are used for supply rail decoupling. Make sure you use the proper polarity when installing! Remember this circuit is powered by + and - 12 VDC including a ground.
C 17..... 330PF.
C5, C6, C7 & C8 ..... 4700 PF Multi Layer Ceramic or Equivalent.
C13, C14, C20, C21, C24, C25, C28, C29, C32, C33, C36, C37, C40 & C41 ..... 2.2 UF Multi Layer Ceramic. These capacitors determine the bandpass of your receiver! Note: A value of 2.2 UF creates a bandwidth of approximately 0 Hz. to 18 Hz. with a cutoff frequency beginning at 12 Hz. I use this value as my main interest only lies with the first Schumann Resonance at 7.83 Hz. To increase the bandpass simply change all values of the above capacitors accordingly. Example: Using a value of .33 UF a bandpass of approximately 0 Hz. to 50 Hz. will be achieved enabling observation of all Schumann Resonances.
Final Comments
I use the above Preamp / Signal Conditioner in the field. It is powered by 12 VDC Deep Cycle lead acid batteries. Two are needed to create the + - 12VDC with a ground to feed the Op-Amp Rail Supply. This system may also be used if 120 VAC is available with a well filtered and Regulated DC Power Supply. In the field I have found two 12 VDC batteries rated at 7 AH will last extremely long. How long is hard to say as I have never depleted them between charges.