General discussion thread:
Some resistor and trimmer references are incorrect included in the initial BOM.
Please download a recent version of the BOM (20/11/2018 or later).
The offset compensation on the filter boards do not allow easy fine-tuning.
In case of an inaccurate setting of the trimmers, the LM741 opamp immediately saturates.
See page 11 how to easily fix this.
To adjust the LM741 bias exactly to 0,00 mV on the low pass filter and high pass filter, there is a minor modification on both PCB's required.
See page 12 how to easily fix this.