why would KM84 not work with phantom from a Neve?

I helped a friend of mine build a pair of my JC1272 design, and they sound great, but the phantom power doesn't seem to power his Neumann KM84. His AKG C460 works great with it, but not the KM84. the Neumann does work with other preamps, however.

The phantom supply on the Neve is a true 48vdc fed through matched 6.81k resistors directly to pins 2 and 3 on the XLR inputs. I'm not sure what the current is, but my understanding is that the KM84 (and most other transformer-coupled condenser mics) don't need much more than 1mA to function properly.

FWIW the AKG C460 is transformer-balanced as well, and it works fine.

I remember something about early Earthworks mics that caused them not to work with transformer-coupled mic preamp inputs.... something like one leg pulled more current than the other or some such, but I don't believe this is true of the KM84.

Does anyone have any ideas? I haven't tried his mic with my own Neve builds to see if it works yet. I just thought I'd go ahead and throw the question out to you gents to see if anyone had and idea of why this would happen.

:?: :?: :?

JC

PS - if this subject has already been discussed elsewhere on these forums please accept my apology for the repeat. I searched for relevant threads but found none. -JC

Have you actually measured the voltage on pins 2 & 3 referred to pin 1? The KM 84 is exceptionally picky about phantom voltages; if the unloaded voltage is less than 45 volts, it won't work.

Edit: Also, have you tried a different mic cable?

Peace,
Paul

Good thoughts, Paul, thanks. I'm going to head over to his place, probably tomorrow, to try some different combinations as well as try his KM84 with some of my own Neves.

And I'll be sure to verify the actual voltage at pins 2 and 3.

Thanks,

JC

BTW, it's a very late response, but yeah, the phantom supply on his preamp was only putting out 27 volts.

[just wanted to close this thread in case this info can be helpful to somebody].

JC