The second is the choice of the input FET. The schoeps uses a BC264 which has an input capacitance of 4pF, and the dorsey uses a 2SK170 with an input capacitance of 30 pF. Considering the very high impedance at that point, isn't such a large input capacitance a bit of a problem?
At 16kHz the BC264 should have a input reactance of 2.5M (already quite small compared to the 1G precharge resistor), the 2SK170 on the other hand only 330k. Wouldn't it be better to use the BC264, despite the slightly higher noise figure?
The choice of 2SK170 is completely wrong, as used in Dorsey mod (as well as in many commercial mics). Having said that, it might be a very good choice, once all the voltages and operating points set right. Just look carefully at its data sheet to find the answers, otherwise, use what Schoeps does (and leave in the biasing pot). Look for Zapnspark messages concerning the right procedure of biasing.
Best, M