Alesis 1622 Reference Manual page 37

diminished. If the power amp has a grounded type plug (3 pin), use a 3 to
2 pin adapter (ground lift) instead of flipping the plug.
C) Plug in each tape machine and outboard effects device one at a time.
Either use a ground lifter or flip the polarity until the quietest position is
found.
D) You should've done this in the first place, but in case you haven't yet, make
sure that all of the audio cables are in working order.
detached ground wire will cause a very loud hum!!
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Cables with a