[LAU] Recommended USB interface with 2 XLR inputs?

Mark Knecht markknecht at gmail.com
Mon May 2 21:17:05 UTC 2011


On Mon, May 2, 2011 at 3:19 AM, Hakan Koseoglu <hakan at koseoglu.org> wrote:
> On 1 May 2011 18:51, Mark Knecht <markknecht at gmail.com> wrote:
>> As far as I can tell, no, I don't. I own a couple of USB hubs and 4
>> external hard drives. None of them functioned at all when attached
>> without their power supplies.
> According to the proper USB1/2 specs, you're only supposed to feed
> 0.5A at 5V (a measly 2.5W!) to an individual port. Now, most USB
> chipsets don't have the necessary hardware to achieve this and will
> provide up to 2A for a bus of four, letting any device draw as much
> current as they require (10W!). Most hard disks, on the other hand,
> will require more than 0.5A at 5V. Thus if you have a compliant
> machine, they won't work. If you have a dodgy machine with no
> isolation between the USB devices, it's more likely to work! Hubs
> without their own power supply draw the power from the mother board,
> making the power issue even more of an issue (4 devices served by a
> 0.5A current source).
>
> All of this means that since none of your hard drives works, your
> machine has a good, proper implementation of the spec with isolation
> between individual ports plugged into the same internal bus. Also it
> means any device that's completely broken in power requirement will
> struggle.
>
> Even different machines from the same manufacturer has issues. My Dell
> laptop can't drive one of my disks but a Dell PC can.
>
> USB3 has increased the individual current amount to 0.9A at 5V (4.5W).
> Most likely the implementation will be broken and a whole pile of USB
> powered devices will arrive soon, drawing massive amount of power
> (18-20W?).
> --
> Hakan (m1fcj) - http://www.hititgunesi.org
>

Hi Hakan,

OK, so I guess obviously the USB port must supply some amount power or
even a simple flash drive wouldn't work as the memory in it has to
require some sort of +/- supplies to function at all.

In terms of my external USB hard drive, I have 3 like the following
link except mine are 500GB.

http://www.amazon.com/Buffalo-Technology-DriveStation-External-HD-CX500U2/dp/B002IYDEMW

This drive ships with an external wall wart power supply and doesn't
function without it on any machine I've plugged it into.

I think what I've going to do is drop by Guitar Center and see if they
have any open devices they will allow me to plug into my laptop, just
to see if they are recognized at all.

Cheers,
Mark


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