So, you just got back from the car audio shop. You have been saving up for the last 3 weeks to get that bright shiny amplifier that is going to send your subs right through the seats. you get it home and take it out of the box, then immediately install it in your car. you crank up the volume on your head unit and something is not right! This hunk of metal that is supposed to drive you out of your car is simply driving you insane!
What you neglected to check was the gain on the amplifier. Now before you start poking and turning knobs, there are some things you should know. First, the gain knob is NOT a volume knob. The volume knob is on your head unit. The gain knob on your amplifier is a way of matching the output from your head unit to the amplifiers input. Since no 2 head units are created equal, we have to have a way to interface the two pieces of equipment. Some head units put out 4V of signal, some put out 8V or more. Some only put out 0.5-1V. So you ask “why is this important?”, “why do I care what my head unit puts out?” Since amplifier companies dont know how much signal your head unit is capable of producing, they had to come up with a way to allow their products to be connected to any head unit out there. Hence the gain control on your amplifier.
So what does the gain control do? Anyone who has had an amplifier will tell you that it controls how loud the amplifier gets, right? Well, yes, it does do that. But it doesnt do it in the way you think. If you look at the control you will see that it has a range of 0.1 to 10 volts input. Some companies break that into two ranges with a “X1 and X10” switch. What that really means is that if you have it set on 0.1 volts, the amplifier will put out its full rated power, with only 0.1 volts of signal input. This is as sensitive as the amplifier will get. (There are side effects to making it that sensitive, but we wont get it that for this article. Just realize that turning it all the way up has some undesirable effects.) if you set it for 5V input, then it will take 5V of input from your head unit to drive the amplifier to full rated power. What this means for the user is that you can match the output of your head unit to the amplifier with the least amount of distortion.
So now we get to the point of this excersise. You want your amplifier to put out as much clean power as it can, so, matching it is important. There are a few different ways to match an amplifier to your head unit, we will discuss a couple of them here today.
The first method is also the simplest if you know what you head unit output voltage is. Now I would like to clarify, the voltage I am talking about is the voltage that is coming out of the RCA connectors from the head unit. If you know what the voltage is, then simply set the amplifier for that voltage, you will be in the ballpark. You may have to adjust it slightly. If you have multiple amplifiers you may have to adjust it slightly to mix the music together (ex: if you have a seperate amplifier for your tweeters and mid-bass you will want to adjust the gain to mix those two speakers to create a good balance.) just keep in mind that if you turn a gain up too high, you will overdrive the amplifier input circuits and could cause damage. Either way it certainly wont sound very nice.
The second method will require a DMM. (digital multi-meter) You will have to contact the amplifier manufacturer to get the output voltage (speaker connectors) that your amplifier puts out at full rated power. This can also be calculated using a simple formula. If you have a 500watts x 1 amplifier then use the following as an example. Sqrt(500) = 22V. That will be the most that amplifier can put out. Now turn up your head unit 3/4 of the way up and play a test CD track at 30-40hz. With the DMM measure the voltage of the speaker output. Turn up the gain on the amplifier until it reads 22V AC. (make sure you do not have the meter set to DC) This will set the gain to its highest settable point without over driving the amplifier.
Well, that is it. Its not too hard once you understand what the gain does on an amplifier. I hope this has cleared up any confusion and has helped you with creating a better sounding system in your car.