Audiophilepure

https://stereo-magazine.com/article/audiophile-mobile-usb-dac-by-cayin

The best solution for the R-2R circuitry is to obtain the highest possible incoming bit-stream level and then apply a high-quality analog volume control after the signal is converted by the R-2R DAC. Therefore, Cayin recommends using a music player app for the smart device that supports Bit Perfect USB, bypassing the volume control of the source device.

An optional adapter cable is also available for devices with a Lightning connector. Two headphone outputs with 3.5 mm and 4.4 mm jacks are placed on the connection panel. The user can also choose between oversampling (with upsampling to 384kHz) or non-oversampling.