One of the last steps in installing an amplifier is to set its gain correctly. The gain setting matches the input level of your amplifier to the output level of your receiver, ensuring maximum distortion-free music and minimum background noise. This process is also called "gaining in", as it is used to correctly adjust the "gain" or "level" knob. If your amplifier has a clipping LED, disconnect all speakers and only pay attention to the clipping LED instead of the distortion of the sound.
Start with all EQ presets and tone controls on the radio turned off or set to low. Turn off all filters on your amplifier, set the bass boost to zero and turn the gain to a low value.
Play some familiar music and turn up the volume on the radio until you hear the music start to distort, then turn it down a little to make it sound clean. If you don't hear distortion even at full volume, turn the volume of the radio to ¾ full.
Slowly turn up the gain on your amplifier until you hear the music start to distort or the clipping light comes on, then turn it down a little so it sounds clean again and the clipping light goes out.
Reduce the volume of the receiver to a comfortable level. Play the familiar song over and over while you continue to adjust your system.
Adjust the EQ presets or tone controls on the receiver to how you want to hear your music.
For a 2 or 4-channel full-range amplifier, turn on the amplifier's high-pass filter and adjust it to remove the lowest bass tones from the full-range speakers. These low tones would likely be the first to distort through the speakers when you turn up the volume later. With subwoofer amplifiers, you turn on the low pass filter and remove everything that is not bass from the sound of the subwoofer.
The bass boost is another type of EQ or tone control, usually related to a particularly low tone. Experiment with it carefully and listen to how it affects the sound of the bass and adjust it to your liking.
Readjust the gain control on the amplifier - first turn down the gain on the amplifier and then repeat steps 2 and 3. Turn up the volume on the receiver until you hear the music start to distort and then turn it down a little to make it sound clean. If you don't hear any distortion even at full volume, turn the receiver volume up to ¾ full.
Slowly turn up the gain control on your amplifier until you hear the music start to distort, then turn it down a little to make it sound clean again.
Re-adjusting the gain (the last two steps) is important to compensate for any EQ or boost effects so that the gain of your amplifier is set exactly the way you hear your music.
