Alessandro \$m[1]:What about powering with +-24 V (i.e. using lead acid batteries)? I need for an indipendent and fully isolated 2 channells pre.
You need both + and - DC, plus if you want phantom power you need another 48V supply. So assuming that 24V was enough to keep the regulators happy, you could do it with six 12V batteries. Not exactly portable.
What you really need is a power supply that takes a more reasonable DC voltage and has a bunch of DC-DC conversion to produce the necessary voltages to run the pre. Then you should be able to run it with a more reasonable source of power. (I've got a Sound Devices field recorder that uses standard camcorder batteries, for example, and will run all day on one, including providing phantom power and spinning a disk drive and cranking a bunch of LEDs. I doubt that a single mic pre requires a whole lot of power.)