> Thank you very much for your detailed answer.
>
>
> And yes, linearity is important for me.
> If it's not too much work for you, could you please tell me which
> resistors I have to change, and what would be the new values
>
>
> Regards,
>
>
> Thomas

You have to increase the values of the resistors that define the
amplification of the circuit (nothing but the standard circuit of an
inverting amplifier with opamp) by the same factor. These are the 47k and
100k resistors of the unit in question (R1, R6, R11 = 100k and R4, R9, R13 =
47k for the sub-units 1, 2, 3).

You may replace e.g. 47k by 470k and 100k by 1M.

Good luck
Dieter Doepfer