Think about this... if you use the WA8 while it is plugged in, does the battery drain? I think it is like my Fostex HP-P1 -- the power for amplification is drawn from the battery, but the battery stays nearly fully charged. That implies that the battery is still connected to the wall and will thus transmit noise like any conductor. I'd be happy for Woo or an EE to correct me, if I'm misunderstanding.
3/29/16 at 4:38pm