Hello all,
I am Rico from Euler Precision.
As we have seen, there is a lively discussion about the function of the "DC-Servo" circuit.
Here now the solution of the mystery:
The circuit consists of the components C101, R103 and the DC Servo loop U203, R105, C103, R106 and R107. These represent an integrator which is limited in bandwidth (C103 // R105 and C103*(R106+R107) and gain (R105 / (R106+R107).
As some have already noticed, the theoretical cutoff frequency is above 100mHz. However, since the large capacitors also have a larger tolerance, we were able to measure that this cutoff frequency is 105mHz (-3dB) for our product over all stages.
The input filter consists of the components C101 and R103 (-20dB/dec) and the integrator (-20dB/dec) and is therefore a 2nd order filter.
R109 is not equipped. This resistor is intended for service purposes.
We hope to have brought a little more light into the darkness with our explanation.
Many greetings Rico