Hi everybody. I have just bought an external DAC with amp (amp is supplied by external AC adapter) that is connected via USB OTG to a Samsung Galaxy S3. Because the DAC is USB-powered I could see my battery on the Galaxy drain fast when listening to music @ work.
Because of that, and because the DAC requires 150 mA and the Galaxy only can output 100 mA, I decided to buy a USB hub…A Belkin 4 ports with external 5 V supply.
However, when I connect the Galaxy to the DAC via the USB hub, there is music out of the DAC/amp even if I do not connect the power cable to the USB hub!!
It seems that the 5 V supply of the USB hub is just connected in parallel with the 5 V supply from the Galaxy. As the DAC function as load to the 5 V supply, the current supplied by the Galaxy and the USB hub, respectively, will depend on the impedances of the cables according to current division.
I would like the USB hub to supply all power to the DAC. I have read a number of DIY USB hub guides saying that the 5 V pin on the USB cable between the Galaxy and the USB hub should be disconnected, to force the DAC only to be powered from the hub. I have tried that, but then the Galaxy does not recognize the DAC and simply plays music out of the internal speakers.
Have anybody experienced the same phenomenon? I don’t know why the Galaxy has to be connected to the 5 V of the DAC to recognize the connection.
Will the solution perhaps be a series resistance of e.g. 1k Ohms connected in the 5 V wire between the Galaxy and the USB hub?
My setup is a mess of different USB cables, as I do not have all the prober cables yet, but it should not matter. It is as following:
Samsung S3 USB audio > USB OTG micro-b to USB A female > USB A male to USB mini-b > Belkin USB hub > USB A male to USB mini-B > DAC
Edited by DonJunker - 7/8/13 at 10:02am