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Music servers and other computer based digital audio technologies.

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iPad and external DACs

Posted by soundchekk on August 17, 2012 at 01:57:52:
Hi there.

The iPad allows to connect external USB DACs via CCK... ...under certain conditions.

iPeng - the iPad player app - meanwhile supports up 2 24/96 playback (even as PCM stream) (- iPhone is limited to 48khz.)

To me all this looks quite attractive on the first glance.

As usual, there's always a "but".

Problem:

USB power.

Obviously the iPad won't power USB DACs with rather high (>100mA???)power consumption.

The problem is that even self powered devices ( not all -- but many ) - if directly connected - won't work.

iOS will complain about too much power consumption.

I did a test by using a USB cable with cut off 5V. No change.
I did another test by powering up the iPAD with DAC connected ( somebody suggested this). No change.

The only way to make it work was by hooking up a selfpowered USB-Hub in between iPAD and DAC.

Scratching my head, hmmh... ...I guessed - it must be a software/firmware issue.

Finally I stepped over a comment that stated that USB devices
need to announce estimated power consumption to the host.

Question:

Could it be that all those selfpowered USB-DACs that just work with
a hub in the line, don't announce the power consumption to the host??

That's just a thought. Would be nice if affected manfuctarers would look into the subject. Similar things might happen on Android devices soon.

Cheers