A marine amplifier is subject to strong humidity rather than salt. In fact, the amplifier is normally installed in a locker, preferably not far from the battery packs, which often coincides with an area not free from the effects of humidity.
Setting aside the summer period, the whole boat is always subject to high levels of humidity that often in the lockers becomes more consistent, so that the internal components of an amplifier are subject to a continuous aggression of this element.
While the stereo player can be removed in winter, this is more difficult for an amplifier which will then have to lend even more efficient marinizing techniques.
In addition, a marine amplifier must have the inputs of the various cables sealed or protected by special doors with gaskets.