I have RFI tested several Schoeps style mics with the 10, 15 or 22nF wired capacitors mounted on the PCB and on the XLR. YMMV, but in my tests it made
no difference as far as RFI sensitivity is concerned when I injected RF signals between 500 and 1200 MHz. Those capacitors act more like inductors the way they are mounted. If you want optimal RF interference suppression, the PCB and circuit design and the pin1 to mic body connections should be
designed with RF in mind.
Although I'm afraid it will prove difficult to make a mic RF proof when the transformer and its wires are close to the XLR and there is hardly any space for beads and other stuff others have already mentioned in this thread. Yet, I have designed a PCB for the CM-60, based on the KM84 circuit and added a ferrite bead between pin 1 and signal ground. I just want to give it a try and don't want to rule out that it helps. A common mode filter + beads + XLR with built-in spring-loaded contact to the mic tube as in the CM-63 will for sure work better, but is not an option here.
Btw, talking about the ferrite bead: in the original KM84 circuit, there is a 10 Ohm resistor between pin 1 and circuit ground. Don't know whether this is for hum or RF suppression or both. Anyway, it is not on the MP and Graeme's PCBAs, maybe due to a lack of space or other reasons? But MP
did include this resistor on the LDC version of the KM-84. Does anyone know why? What surprises me, by the way, is where Neumann decided to make the connection of the mic tube to the circuit: it is connected to signal ground at the impedance buffer side of R13 instead of to pin 1. This means there is an interruption of the Faraday shield, which should be contiguous.
Jan