How many of you out there know what the gain structure of your sound system is? If you think it has something to do with the material used to build your amp rack, then you definitely need to read this month's column. One of the most common problems I see in the judging lanes (especially with beginning competitors) is a complete lack of proper gain settings in their systems. This is a very important and often overlooked step that must be done correctly when dialing in a competition system.
The question of the month this time prompted me to dedicate the entire column to this often-overlooked subject. The reader has a head unit, a crossover, and three amplifiers in his system, and he asked how he could most effectively set up the gains to get the most out of it, without using any expensive tools. Many articles have been written on gain-setting over the years, and most of them involve using an oscilloscope along with some other specialized equipment. While using these tools is the best way to get optimized gain settings, most people don't readily have access to them. With that in mind, let's show you how to set up your system using only your ears and a good demo CD.
The key to proper gain settings in any system is to maximize the potential of every piece of equipment in the signal chain. If any part of the chain is not optimized, the whole system will suffer. In most systems, the first part of the chain is the head unit. The idea here is to figure out how much output the head unit has before it clips, or distorts, the signal coming out of the RCA's. Normally, you would put in a test CD and hook up the RCA's to an oscilloscope, but since we don't have one available, let's do it another way. First, turn the gains on your amps all the way down, along with any other gains in the signal chain. Now, put in a CD that you are familiar with, one that is well-recorded and that has a strong output level. Turn the head unit's volume up slowly and listen for distortion. This won't damage your speakers since you turned the amp gains down, so don't be afraid to turn it up all the way. Once you hear distortion, back off the head unit's volume slightly, and you have just figured out the maximum output of your head unit. Remember this volume setting, and don't turn it up any louder. If you do, your system will sound distorted. If you don't hear any distortion at full volume, congratulations, you purchased a quality deck.
Now, let's move on to the next piece of equipment in the signal chain. In most competition-type systems, this will be an equalizer or a crossover. Many of these have an input and an output gain, while some have one for the output only. The head unit should still be on its maximum undistorted volume for this step, with your familiar CD still playing. Slowly turn up the input gain until you hear distortion or until the clipping indicator on the component starts to flash. Back off the gain slightly, and now the equalizer or crossover is receiving the maximum available signal from the head unit. Next, turn up the output gain until you hear distortion from the speakers, and back it off slightly. Now the equalizer or crossover is sending the maximum undistorted signal to the next component in line. Continue this process until you get to the last components in the chain, which are probably the amplifiers.
At this point, gain setting really becomes a judgement call. Since the signal is maximized all the way to the amps, the only gain control left is on the amplifiers themselves. These gains can be turned up until the speakers or amplifiers distort, so you have to decide how loud you want your system to be. For a normal street system, louder is probably better, so turn the gains up until you hear distortion again (you might want to use earplugs this time) and back the gains off slightly. You have now optimized the entire signal path in your car, and you can enjoy the full capabilities of your equipment.