فلزیاب پالسی فلزجو - FelezJoo PI

Thanks.
1- R9 is 1M and R10 is 100 ohm.
2- We have only a simple and powerful HIGH pass filter that implemented as C11=2.2uF for reduction 50Hz (or 60Hz in other countries) electrical noise. This value is critical for circuit to work correctly and block electrical noise as well. Low pass filter implemented simply by a 5pF (C10) filter with about 32Khz cut off frequency and it works nice to filter higher frequencies. Of course we can't rise it due to discrimination parameters.
3- I saw elsewhere that Op-Amp magnification of this project is 10000 !!!(?) I suggest you and those people to study more about simplest hints of Operational Amps! Did you just see a 100 Ohm resistor in input of LF357? Please note for small signal we have R11=390 ohm and total impedance in input of LF357 will be 490 ohm plus C11 reactance!!! So firstly, we have not a static magnification factor and it is dynamic. Secondly, maximum magnification for high frequencies(such as 10Khz in here) will be 2000. In fact for 50Hz electrical noise, magnification factor will be about 500, while for main frequency domain that we need, amplification factor is between 1000 and 2000!
In this case, two stage amplification doesn't help. Basically magnification with a factor greater than 2000 will not useful in PI projects at all. I've tested it in the past. Magnification factor 1000-2000 does not require two stage of op amps. The result will be worse! One stage amplification with a good Op-Amp and accurate values is better and easier too!