The objective of an audio amplifier is to boost the incoming audio signal that is supplied by a radio or receiver. When we say audio signal, we mean a low voltage electrical current that a radio outputs which has all the information of your musical selection in it. The typical audio signal from a CD player averages about 0.5-2V which is not enough to power an audio speaker or subwoofer by itself; this is why we need amplifiers. The amplifier will turn that 0.5V into 20V or more and feed that to the speakers, which in turn produce music that we can hear. Ok great to know, but what is the “gain” knob on my amplifier?
If you adjust the gain knob while listening to your music playing, you will notice an increase and decrease in volume. However, this does not mean the gain control is a volume control. Let’s repeat that. Your gain knob is NOT a volume control knob. Got it? Confusing? YES! The purpose of the gain control is to level match the head unit’s output voltage (around 0.5V) to the gain structure of the amplifier (how much it amplifies a signal) so that the signal is not over driven which would produce clipping and distortion.
Think of it like this, you have two radios and each of them has a volume knob that goes from 0 to 30. One radio outputs a signal at 0.5V and the other outputs that same signal but at a whopping 5V. The amplifier will amplifier both of those voltages by the same percentage. Turn both radios to a volume of 15 (halfway), will the loudness of the music be the same for both? NO! The 5V radio will sound much louder in comparison to the radio only putting out 0.5V. Now turn both radios to a volume level of 30, which is maximum volume. What will happen? The 0.5V radio will sound loud, but the 5V radio will have damaged your equipment, exploded, or sent the amplifier into protection mode. This is where the gain comes in. Using the gain, your radio’s maximum volume will make the amplifier loud but not damaging. The 0.5V will be loud and the 5V will be louder but won’t damage anything. You can set the gain to a point where your equipment gets loud at about 3/4th of your total volume swing (ex: 0-30).