USB DAC charging itself from phone

[Johnpj]

Hello,

I have had (almost) no trouble getting the usb dac, fiio q1 Mk II to work via the usb connection (with the app USB audio pro).  But the device insists on being charged from the phone, which is speedily using up the power in the phone.  I don't understand why there isn't more on this anywhere, just references to using data only usb cables to improve sound quality.  Is there anyway to have the usb dac stop the power out of the phone?  It does have its own rechargeable battery.  I don't know if a data only cable would solve it, apparently usb power might still be important for some reason.  And these types of cables are next to impossible to find.  The ones on ebay don't have the ground connection which is wrong I read.  I was going to post this on the fiio forum too if that makes a difference.

[NunoSEN2]

Hi @Johnpj;

Have you tried changing the USB connection mode under settings >Device Connection >USB Connectivity?

Try also changing USB configuration in the Developer options.

[Johnpj]

USB connectivity only shows via the pull down notifications.  It is greyed out via the settings menu.  It shows at 'supply power'.  I've tried the various options and they don't help.  'Transfer files' causes the device to stop being charged and stops it working as well.

Under 'developer options' it already shows as MTP (media transfer protocol).  I tried 'audio source' and it made no difference and also RNDIS (USB Ethernet).  The rest are Charging, PTP and MIDI.

'Charging' does nothing too.

I guess most people just use these things like this.  I don't like how the phone charge keeps going down fast.