The adapter you're asking about isn't trivial to make. The problem here is that the 3-pin XLR mic connections expect a balanced signal, but the stereo outputs that come out on the 5-pin Alembic XLR are unbalanced signals. They just happen to be on a similar family of connectors.
The Alembic outputs have a hot and ground conductor. That's like a regular passive bass plus a buffering preamp that makes a low-impedance output that eliminates interactions from cables and the amp front-end.
That's different than the balanced wiring of a microphone. On a mic, the signal is carried on a matched set of conductors and is completely separate from the grounding and shields. At the signal source and mixing board end there are transformers that recover the signal by recreating the difference between the +/- signal conductors. Inside the mic cable, the +/- conductors are twisted together tightly. If the cable passes through an electromagnetic field that would cause hum, both the +/- wires pick up the noise, but the differential combination at the receiving end will remove anything that wasn't at the source. This kind of noise reduction doesn't work with unbalanced connections (like an instrument).
You actually can connect the two conductors of an unbalanced connection to a balanced input, but you won't gain any of the normal benefits of the 3-wire connection.
The adapter you want to make would basically be two DI boxes. The transformer or active circuit in the DI box is what makes the conversion from unbalanced to a differential signal. You could put a DI transformer in the bass, but if you wanted to keep stereo out, you need even more pins on the connector.
On the Alembic 5-pin connector, there are two unbalanced, lo-z + signal outs, a common ground, and +/- remote power from from the power supply. The onboard batteries are a perfect power supply - since the power comes from chemistry, there's no opportunity for hum to leak in. Putting the AC power supply in the blue box lets Alembic make a super-high quality filtered power supply with low noise. This is really a remote power supply since there are dedicated power wires in the cable.
A phantom power supply is a clever trick that takes advantage of the differential microphone connection. They actually pump 48VDC power down the microphone signal lines. The microphone can be powered by connecting to the signal lines, but when you take the difference between the signal lines, the DC power is cancelled out. Many mixing boards provide enough power to power your bass, but you can't be sure of that. Microphones usually only need a small amount of power to charge a mic element, but your bass is powering a bunch of preamps, and maybe LEDs too.
David Fung
