Condenser microphones require some sort of power source, this can be via an internal battery or some require an external +48Volt (phantom) power source. This will depend on your particular microphone. What you need to know is that the synthesizer does NOT supply this power. So you will need to get power for the microphone from some thing other than the XF input.

You can plug the microphone into a capable preamp or a small format mixer that can provide the phantom power, then feed the output of that as a LINE level signal to the XF's A/D input.

The advantage of recording your input through the XF is how you can process the signal prior to recording. The A/D Input of the XF has far more processing available than your typical expensive audio interface or small format mixer. You have the ability to route the A/D input through two studio-grade Insertion Effects before routing it as pristine 24-bit audio to your favorite DAW. You would be very hard pressed to try to improve upon the quality of your recording over what you'll get using the A/D Input through the XF and onto your computer via FW.

Could you improve upon it? well, sure, but not without a huge investment in gear. I highly recommend you get into recording with what you already own (given the investment you would need to make improving on it).

Condenser microphones can be warm and give a big sound, but they are not, simply by their nature, better than a good dynamic mic. Choose your microphone wisely.

Here is an article on setting up a microphone with the XF
(If you use a preamp for your condenser, then you would set the source to "Line" instead of "Mic")
Setting up a Microphone Motif XF

Here's an article on assigning the A/D Input to a FW Bus for recording:
Assigning a Mic to a FW Bus

I agree with what Bad Mister says.

Though….
I had condensers microphones before my first XF arrived. KSM44a and Sennheiser e965
I found out that all I needed was a small mixer, so of course, I picked Yamaha. (The Photo of MG102c)
This particular model of course, has been discontinued. 🙂
However, the replacement models are still moderately priced and are included below.
These 4 are U.S. prices and retailer MG10c or MG12XU are my choices.
I didn’t need too many inputs, only Phantom Power.
The help I can also offer is, put a set of good headphones into the mixer and keep the input knob of the XF A/D as low as possible. Adjust the volume of the mixer beginning with very low, then up higher until the sound is the way you want making sure the XF knob for A/D is about 25% (what mine says now) 50% is never higher.
Using both L and Right of the XF's A/D while using LINE not mic, and keeping the gain of both to a minimum, these stereo mixers sound more expensive than they are and with surprisingly low noise if gain, output, and equalizer settings are low and subtle adjustments. The Gain of each is most important and must be as low as possible.
To understand the reasoning of this instruction is; basically, both the A/D input and the mixer are power producers which is never a good thing.
And, if you pick the model with 'U' at the end, be certain to understand, that means it’s USB which is not needed when FW16e is managing the XF in the on position.
(usb of the my mixer comes in handy when/if I wish to just lay down a vocal track/s on Cubase without using the XF as the audio interface.)

Luck to You

Thanks for your responces.Finaly I think is a good way to record the voices trough the AD input of my motif with my condensed mic but I need to know if I only need to connect the mic previusly to a phantom power or I need too a preamp for the mic?
Sorry about my english

Finaly I think is a good way to record the voices trough the AD input of my motif with my condensed mic but I need to know if I only need to connect the mic previusly to a phantom power or I need too a preamp for the mic?
Sorry about my english

Hi Joan
I only know from my own experiences.
Please post information on the Phantom Power you are speaking about. Brand/Model Number
This way others as well as myself might know about the need for a pre-amp.
Straight away, I would not think so but I dislike guessing. 🙂
*What language are you comfortable with?

Hi Bubba, thanks for your answer,

well, I was thinking to buy a cheap model like behringer PS400 supossing that the only funtction of it is to trasmit phantom power to the mic and don't altered the quality of the signal.
But My question is . Do the Motif have an pre amp to the mic? It's necessary?
I would get a better quality in the sound of the recording of voices with a pre amp for my mic ?

by the way, my mic is an Rode NT1 A

I do not know. I know nothing about Behringer.
As I stated before, I stayed with Yamaha, with the small mixing board which comes in handy for us as we have several condenser mics capturing different instruments and human voices. This is what works. They are very clean and quiet and though a bit more money, they were tried and they work.
Again, it is very most important to keep the AD knob of the XF at the lowest GAIN setting when adding 48 volt phantom power regardless where it’s coming from. I don’t believe it’s wise to use it as a volume control because it says 'Gain' ! 😀
... I always believe, whether it is true or not, same manufacturers sometimes cooperate better with same manufacturers.
(Yamaha Mixer Yamaha Motif XF) I added headphones as well. Works great, sounds great.
I know also what it’s like to be limited with funds. no problem here 🙁

Maybe someone else 'round these parts, might have some more info on that Behringer phantom power you’re interested in.
Stay hopeful and keep trying... while being very cautious with voltage going into the back of the XF.