In the case of the M-audio supplying phantom power it obviously must
be switching noise converting 5 volts to 48 volts.

I have not heard from M-Audio yet (holidays?) if this is a known issue
that can be fixed.

I have always wanted portable hardware that was not powered from
the computer's bus. The Echo products seem quiet but you must lug all
that hardware around and you need a mic preamp with phantom power
that is powered by its own power source.

When recording video and using a mic adapter (Beachtek) I found
the sound was quieter when on batteries than with an AC adaptor
powering the camera. A grounding issue?

Never had any problems when using a rented pro camera with
built in XLR mic inputs. (get what you pay for?)

I want to use the Laptop and interface so I can burn an evaluation
CD of the performance on the spot but I guess I need to invest in a
van for a mobile studio.

Let you know what I found out.

This sounds very similar to a problem I encountered with my USB sound card by Sound Devices the "USBpre". This device has all the bells and whistles that I needed for doing all the exact same kind of thing you're doing with a laptop. I use this card on the road and in my office bench setup. I found I could not have anything on the USB bus, besides the sound card because of power limitations. The USB power only provides 500mA max power for devices on the bus. This gave me some issues because for my bench setup I have a USB keyboard to do all the Vegas shortcuts with the numeric keypad and I couldn't have the sound card and the keyboard connected on the bus at the same time because of that power limitation. I wrote to Sound Devices and they acknowledged they had seen my problem and informed me the USBpre would use the full 500mA with phantom power applied and must be used on it's own USB port. I told them I wished the sound card had an option for an external power supply. They agreed but recommended I purchase a USB hub to solve my problem. I haven't used the phantom power, but I would not be surprised if I run into the same kind of issues you are. For phantom power to work you only really need 18-24volts instead of the full 48volts, but the real limitation is the current. Remember Power= Voltage x Current. That would be my best assumption of the problem you're experiencing, too much power required than the USB port can deliver due to the phantom power being on.

I can see this will be a problem for me. not knowing exactly what I would need to do the job. I bought the mobile pre because I could not wait for Digital audio labs " card deluxe usb 2.0" that's due out mid late next year.

what I do is record house music sets in Chicago. I have done 2 " Live " set when we mic the room for crowd noise.I used 2 dats. My plan is to use the card deluxe for dj mixer and mobile pre for the room.

A usb hub will solve the power problem? is one better than another as far as power supply goes ?

not change the subject but if you see more problem I'm not aware of please advise me

Thanks

"A usb hub will solve the power problem? is one better than another as far as power supply goes ?"

For your setup, I would have to say yes. If your laptop only has one USB port like mine does then you will run into this lack of power when connecting 2 sound card devices to 1 USB port. A USB hub has it's own power supply, thus it can provide power to each of the extra USB ports on the hub. The bandwidth of the data will still be the same, because the hub is connecting to the single usb port on your laptop, but each or the USB ports on the hub should have it's own 500mA current, that it won't have to share with all the other ports.

rednroll,

no i have 3 usb 2.0 inputs. i'm thinking the phantom power will be my problem.

i recorded a set last night with the mobile pre. it worked good no problems with 6 hours of recording. the gain were almost bottomed out. it was easy to use.

it sounds like a $150 card. it should work for the live sets but dats sound better.

bill (one hand typing)

I'm not an audio guy but two things:
There's two standards for phantom power, 12V and 48V. Some will run on either, others have a dummy spit. I'd imagine though that a 12V mic run off 48V will be wasting a bit of current so that's not going to help much.

Also consider a DI box to feed phanotom power to the mic, one less drain on the laptop's power supply as well.