Thanks, Merc. I looked at the manual of the AMP, did not say much. The Amp turn on and off through the trigger as I turn the 990 on off. Even if I disable the trigger and leave the AMP on still has no sound. At night time I can hear the voice and sound came out from speaker but so tiny and there is a crack sound or should call it clip sound from speaker whenever I change source and turn on the volume higher or lower, there is always 1 clip with every one step volume change. I am so confused!