API 3124 Phantom Power

I was getting ready for a tracking session at my studio. Bass guitar overdubs and a bit of percussion work. I pulled out a number of microphones and DI boxes including a few Shure SM-57s, a Neumann U87, a Sennheiser MD-421, and a pair of Neumann KM-184s. The KM-184s are a stereo matched pair as pictured above.

I intended to use my API 3124+ as the primary mic preamp. Only something was not right when I tested the KM-184 microphones. All the other microphones worked perfectly. But not the KM-184s.

The KM-184s are small diaphragm condenser microphones and they are generally used for drum overheads, acoustic guitars and certain types of percussion elements. These microphones require 48-volt phantom power. In the trade, the Neumanns are known to be a bit particular about the quality of the phantom power.

When I connected the KM-184s, the meters showed dramatic oscillation and the tracked waveforms showed asymmetric clipping. Not good. And this was true for both of the KM-184 microphones and evident on all 4 channels of the API 3124.

I did not have time to test the KM-184s on my other preamps. I’ll try that this evening. I have used the KM-184s extensively — they have been in my mic collection for about 15 years — but usually with my Millenia or Neve preamps.

I will have to test the API to see if I have any issues with phantom power.

The way to test the unit is to take a multimeter and measure between pin1 and pin2 on an XLR output. I should see +48vdc within about a 3vdc tolerance either way. I will then need to check between pin1 and pin3 and I should see exactly the same reading.

If the readings are not the same and if the levels are outside the +48vdc range, then I can attribute the issue to the preamp chain and I can use a different set of preamps for the KM-184s. If both KM-184s happened to die both at exactly the same time, which I doubt, then I am in a wee bit of trouble for this session. I do not carry any other small diaphragm condensers in the studio and I can’t get something in quickly enough.

I hope the mics still run fine on the other preamps. We’ll see.