For those planning to use this with a phone, you should get the upgraded DAC version as they don't have a line out and you don't want to double amp by connecting to headphone out of phone.
The amp only C5 is only for DAPs that have a fixed line out feature.
For Android, you will need to purchase the appropriate OTG cable.
For iOS, you will need to purchase a CCK cable.
Edit: If one insists on doing phone headphone out to amp, then set phone volume to somewhere between 80 and 90% of max volume to reduce artifact and distortion noise.
Edit: If one insists on doing phone headphone out to amp, then set phone volume to somewhere between 80 and 90% of max volume to reduce artifact and distortion noise.