Hi, with so many phones now dropping the 3.5mm headphone socket I was wondering what the options are for driving proper headphones from them? In this context I'm thinking of headphones like the Sony MDR-1A that can be driven fine from most phones and not super high end cans that have always needed a dedicated amp. I know many of the phones come with usb -> 3.5mm adaptors, are they generally just a pass through of the analogue signals, i.e. the DAC is still in the phone, and do they work as well as driving directly from the phone used to? If not then is some form of portable usb DAC/AMP required now? Thanks for any thoughts.