Yulong D100 MkII Headphone Amp and Line Out Use
First, always use noise-filtered clean power supply. When you connect both line out connector (RCA) to your amp while at the same time plug in the headphone connector, I find that the sound through headphones will be distorted if the amp turned off. If you turn on the amp then the sound will be ok. Disconnect the line connector from D100 is of course ok. But if you use both then this is a little bit annoying having to turn on the amp while you just want to listen via headphones or having to disconnect the RCA connector.