Essentially there was only one problem which I was able to resolve: The bad input and output impedances of the former circuit. I now have a circuit with an input impedance of approximately 100kΩ, and an output impedance of approximately 10kΩ. A source-follower resistor for the output can be substituted where R3 is, to halve the impedance further, at the cost of also attenuating the output amplitude slightly more…
These were the SPICE Model-Cards used:
Please do not attempt to build this circuit using discrete components. As already described in the previous, main posting, the ultra-low capacitances used in this circuit will get overpowered by stray capacitance which breadboards, wires, etc. will introduce. This circuit can only be implemented as part of a larger circuit, on the same IC. Therefore, it should only be considered hypothetical.
(Updated 7/4/2019, 8h20 … )