The gain or level pot is not a volume knob, it is used to match the relative output level (voltage) of your source unit to the input circuit of your amplifier. The gain control determines how far you have to increase the volume on your source unit for the amplifier to reach full power. If you have your gain set too low your amplifier will not be able to reach full power and this could allow the source unit to clip which in turn will result in a distorted signal being delivered to your speakers. This is especially relevant with low voltage sources (lower than 2.5volts typically OEM units). With higher voltage sources (2.5volts or higher) if the gain is set too high the amplifier will be able to reach full power at a lower volume control setting from the source unit. This will allow the amplifier to be driven into clipping. The gain settings should generally be set lower, meaning a higher setting on the volume control of the source, to minimize amplifier clipping.
Guide to Setting Gain Control
If you do not have the correct equipment (oscilloscope) this may help
you to set your gain.
1. Once you have installed the system power it down.
2. adjust the amplifier gain to the minimum.
3. power up the system and adjust the volume control of your source unit
to about 3/4 of the way up.
4. slowly increase the gain control until it reaches the maximum level you
are comfortable with or until it starts to clip, and then reduce the level
until you are happy that you will not damage your speakers or Subwoofer.