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How can USB supply enough power?

Discussion in 'Computers / Software' started by krbusby, Apr 6, 2013.

  1. krbusby

    krbusby Guest

    I just purchased an M-Audio USB Fast Track and was surprised to find it relies completely on USB for its power. How can a 5volt USB port supply enough power for the Phantompower which is 48v? Should I get a powered USB hub?


    Thanks for any feedback.
     
  2. audiokid

    audiokid Staff

    I never rely on USB power. It seems to cause everything from latency to actual distortion. Buy a wall wart indeed! But you asked about a hub, so, I don't know about that. I'm curious what others suggest too.
     
  3. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

    I believe it's works with an oscillator and some caps and diodes. The osc makes AC (sort of), the diodes pump up the voltage and the caps smooth it back out. You trade away current for voltage but you only need 14mA for phantom power. Something like that anyway.
     
  4. Kurt Foster

    Kurt Foster Distinguished Member

    you not only need to power the phantom but that USB "power" is also feeing the mic pre .... we've all heard the advantages of high volt rails in power amps ... SPL's 120 volts etc. Mic levels are very low and the better power supply a mic pre has the better.

    like Chis said .. get the wall wart ... or better yet use outboard preamps, especiallly if you are doing more than one channel at a time.
     
  5. krbusby

    krbusby Guest

    Hey guys, thanks for the interesting info.

    Just a note... there is no option of using a wall-wart as this device doesn't evan have a place to plug one into it. I could use a new USB hub anyway so I guess I'll pick up a powered one in the hopes that this will deal with any power shortcomings in the future.
     
  6. Kurt Foster

    Kurt Foster Distinguished Member

    again, the best thing to do would be to get an outboard mic pre(s) that has real mains power (not a wall wart).
     
  7. mberry593

    mberry593 Active Member

    USB 2.0 can supply up to 500 ma @ 5 volts if it is specified 'high power.'
    USB 3.0 can supply an amazing 100 watts!

    All of this would be more than enough for a reasonable mic preamp & phantom power but USB power is not always implemented properly.....especially in laptops.

    Windows recommendation: Disable power management. Right click on 'my computer', open up 'properties', click on the 'hardware' tab, open up 'device manager', expand the 'universal serial bus controllers' area, right click on each 'root hub', select 'properties', select 'power management', now clear (don't check) the box that reads, "allow computer to turn off this device to save power." This is absolutely essential for some interfaces (***cough mbox3 cough***) and a good idea for others.

    Usually a USB hub is not recommended but I have had direct experience with one terrible Compaq laptop that absolutely required a powered USB hub to work with an audio interface. ........go figure!! do whatever works.


    btw, bouldersound: Yes, you have the right idea. That is a DC - DC converter & yes it does trade current for voltage.
     
  8. krbusby

    krbusby Guest

    Thanks man. Between you and Bouldersound I now have the logic in place. Was just bugging the heck out of me as to how this could work.

    Thanks a heap! (y)

     
  9. McMurphy

    McMurphy Guest

    With our current state-of-the-art chip manufacturers, these DC to DC up converters have become very popular when powering from USB from the computer. Many audio interfaces do not work well at all on hubs. I've had no problems powering up power hungry and gobbling Neumann 87's on Avid, M-Box 2, without issues from IBM, HP, Toshiba, Apple, laptops. However as Mr. Berry pointed out, he had a miserable Compaq, the low-cost division of HP where he had to use a powered hub. But I've actually had some issues with those powered hubs plugged into my laptops and things would go screwy or, I'd have a bad boot up. It would then require a restart. Not good if you're not prepared before the show rolls.

    I also second what has been said about power management on laptops. I turn off all power management, all screensavers, everything. Nothing times out. Nothing turns off, goes to sleep or hibernates. Except maybe the engineer LOL? At least that's what it sounds like on television lately. It's like the audio guy doesn't know the second news anchor is going to start talking LOL? So all I hear lately are guys missing microphone cues, not the computers. Automatic microphone mixers would do a better job than the folks who fall asleep at the switch.

    McMurphy
     
  10. CoyoteTrax

    CoyoteTrax Well-Known Member

    The concept is counter-intuitive for sure but it does work.

    I bought a 2i2 a few months ago just to have an inexpensive interface for my new laptop. Man, was I ever surprised at how the tracks sound. The pre's are actually really nice and far sweeter than USB or FW powered pre's from just 5 years ago. The technology has evolved quite nicely.

    So don't be afraid to go for it.

    BTW, I was planning on having to use my outboard pre's to get any kind of decent power to my mics (4033's, 012's, 4041's, etc.). Haven't had to do that.
     

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