12. Is there a high background noise on the BTR1?

A: Generally the background noise of a bluetooth receiver/amp will be a little higher than the non-bluetooth playing devices. So it may not be suitable for the high-sensivity headphones such as the K3003 or SE846. The sensitiviy of FiiO headphone are moderate, so they can work fine with the BTR1. The volume setting is not synchronized between the Android devices and the BTR1, so if you feel the backround noise is high when using Android devices, you may try adjusting the volume on the Android device to the highest level while adjusting the BTR1's volume to a lower level (the level 6 or level 7 should be suitable)