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[Mickeyrouse]

I'm sure this topic has been discussed here before, but the " search" feture doesn't seem to locate it. So here goes.
 I have just acquired a so-called "red dot" km84. I understand mics indicated by this dot are different impedance  output (50 ohm? )than the non-dotted versions- or maybe I have it backwards. Anyway, I am expecting slightly lower output for this mic compared to a non-dotted KM84 I have, and certainly less than my KM 184's.  Having read that this red dot mic can be changed by modifying transformer output in the mic, how can I tell if this may have already been done by a previous owner? Even if the output seems less by the expected 6 db or so, it would seem  that could possibly be other performance issues, like the capsule. If it is not modified, just what leads are changed? 
   Performance-wise, I am now comparing KM84 vs KM184. Different, yes. I will no longer use the KM184's on drums- just too much fizzy cymbal sound, for example, and the output just too easily overloads the input stages of many of the mic preamps in 500 series racks- the Neve 1073LB is a particular miscreant. Pads help, of course, but I'd rather not.
However, if any acoustic guitar has strings that are past fresh, the 184's seem just the ticket. I don't think the KM184's are the dogs that many label them to be, but they will never be the all-around winner the KM84 can be.

[klaus]

Hello Mickey,
You can only tell for sure what output strapping and padding the mic is set at by opening it up.
There are two areas of interest under the hood:

1. At the edge of the circuit board is an area where the four output wires of the transformer are connected in one of two arrangements to four solder spots. See the diagram on the transformer core for proper series soldering connections of the four wires of the two output coils, or just copy proper connections from this picture: http://www.saturn-sound.com/images%20-%20microphones/neumann%20kmi%20-%20inside%20views.jpg

2. There are also two 47Ω pad resistors installed next to each other (the two on the left edge of the board in the picture below: yellow/purple/black bands). Remove both resistors and bridge the solder traces underneath with solder.

Both measures will give you 200Ω output impedance and full, unattenuated output of the mic.

[Kai]

... Remove both resistors and bridge the solder traces underneath with solder.

You don't need to remove the resistors if you bridge them.

[klaus]

Correct. It's just easier to make clean connections for the two solder bridges when you remove the resistors.