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I'm interested in listening to extremely low frequency band below 100Hz, where the famous Schumann resonances reside. I will use a large T shape antenna together with a very low noise, very high impedance preamplifier. This is my current draft of the preamplifier:

preamplifier schematic

C2 is the SA102A100JARC 10pF ceramic through-hole capacitor. R2 is the SM102035007FE 5GOhm through-hole resistor. C3 is an SMD ALU electrolythic capacitor. The goal is to have a -3dB LP cutoff at 100Hz and as low as possible HP -3dB cutoff (~ 1Hz). VCC is 5 volts. The next stage would probably be a 50Hz twin T notch filter. I would appreciate if you guys can do a quick check of the circuit and maybe suggest some enchancements :) Thanks !

P.S.: R2 and C2 are through-hole because of the guard ring and easier control of the leakage current.

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  • \$\begingroup\$ Get a free sim tool and simulate it. \$\endgroup\$ – Andy aka Jun 16 '18 at 15:22
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This will be very thermal-noise noisy. And has no ESD protection.

Consider this (from dyiAudio "simplistic NJFET RIAA") which uses a 2SKxxxx NJFET, not the default J310

schematic

simulate this circuit – Schematic created using CircuitLab

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The antenna is the crucial part of the design. Typically coils up to a metre in length and located at least 100 metres from any mains power sources. This might be of some help.

Votis, C.I., Tatsis, G., Christofilakis, V. et al. A new portable ELF Schumann resonance receiver: design and detailed analysis of the antenna and the analog front-end. J Wireless Com Network 2018, 155 (2018) doi:10.1186/s13638-018-1157-7

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