Sound quality is not good.

• Ensure all cables are connected properly and that the headphone cable is fully plugged into the headphone jack.
• Adjust the volume levels on both the DAC and audio source.
• Try using a different USB cable (e.g. Q4->USB power cable and PC-USB cable with OTG function; K5 PRO-> USB cable with OTG function), multiple USB ports and with another source.
• Try using different headphones.
• Try using a different headphone microphone two-in-one adapter (if included).
• Test if the issue persists when connecting speakers to the RCA output.
• Check if the issue is still there when connecting to the TV via optical or coaxial input.

If you have any questions or concerns, please don't hesitate to contact support@fosiaudio.com.