I'd like to connect a headphone jack to both speaker outputs of the MiniAmp. The headphone jack (and plug) use common GND. Within the community I found out, that the connectors for the speakers on the MiniAmp are in order + - - +. So I connected GND of headphone jack to - and right pin to + of one speaker connector. Now I get clear sound on right ear. But when connecting GND of headphone jack to - of second speaker connector the sound begins to stutter. What is the correct connection for headphone jack to MiniAmp?