Alright then, now that my life is a bit less crazy for a moment or two, let's move on. Now that everybody has had a brief reminder of all the times they wanted to punch something because you just couldn't solve that noise problem or get the more out of your system without letting the smoke out, let’s talk a bit about the gain on the amplifier and how it may have played a role.
The gain, or sensitivity, adjustment on an amplifier is, in fact, not a volume control knob even though turning it up will most likely increase the audio level! By adjusting the amplifier’s SENSITIVITY to the signal coming in on its inputs, the gain simply allows us to match the output of one component to the input of another. But why do we need to do this? Why can't the amplifier just respond to any level of input? Well it can, and it does, but the real question is; are you maximizing that amplifiers potential, getting it just right, or driving it into clipping?
Let’s start from the beginning, the source unit. Taking a quick look at the specs of a few decks, we see that one has 2 volt outputs while another has 4 volt outputs and even some have 5 volts or higher. We all know that the higher the voltage from the source unit the better right? But, why is it better? A unit stating that it has 2 volt outputs would ideally produce 2 volts of electrical power on its low level outputs at or near max volume with a clean signal, a 4 volt unit would produce 4 and a 5 volt would produce 5. What’s the difference? Nothing, until you take into consideration what this output voltage is intended to do.
Note: Output levels of a source unit, as well as most audio potentiometers are exponential. This means that just because a 2 volt headunit has a max volume level of 40, that doesn’t mean that you get 1 volt at 20 or 1.5 volts at 30. You will, however, most likely get around 2 volts at 40. What you would most likely get at volume 30, or ¾ of the volume, is .75 volts, maybe 1. So, if you were to go with the old, turn it up to ¾ volume idea, then you are losing out on some serious output! You’ll see why it’s such a loss soon.
Now, let’s take that output voltage to the input of the next device in the chain. For simplicity sake, let’s say this is an amplifier. Now, this amplifier has an input sensitivity range of .3V(all the way clockwise) to 5V(all the way counter-clockwise) and we will just say that 2V is in the middle. Where you set your gain determines what the amplifier needs to see at its inputs in order to produce full output.
So you hook up your 2V output headunit to the inputs of the amplifier and you leave the amplifier at minimum (5V). All the amplifier knows is that when it sees 5 volts on its inputs, it needs to be at full output, but you’re never gonna be able to give it 5V are you? So, even if you turn the gain up 1/3 the way, you are still never getting full output from the amplifier. Sure, you get sound, but there’s no real excitement to it and even with the radio volume at max, the system is just not loud.
So, let’s take it all the way clockwise, now you’re telling the amplifier that when it sees .3V on its input stage then it should be at full power. Well, this is going to happen pretty quickly isn’t it? It will probably be somewhere around volume 20 or so and any increase in volume above this level will most likely result in a clipped and distorted signal which will damage the speakers and sound bad. So now you notice that you can’t seem to find the right volume level, 15 is too quiet and 16, too loud. You also notice that when the volume is low, you can hear a hissing noise and a high pitched whining noise that responds to engine speed. Both situations have to do with the fact that you have made the amplifier TOO SENSITIVE to incoming signal. So the smallest change in the output voltage of the headunit equates to a large change in the output of the amplifier and the amplifier is so sensitive that it is picking up on unwanted signals as well as the audio signal.
Note: The high pitched whine can also be, and in most cases is, caused by inducted noise. This happens when the signal cables (rca cables) are run too close to the power wire or some electrical components that create a magnetic field around them while operating, which infects the audio signal. While keeping control of the gain can minimize the effects of this problem, simply re-running the cables and killing the noise is the right way to do it.
So now let’s say that you put the amplifier gain right in the middle, 2V, the magic number we have been dancing around this whole time. Now, when you turn the radio volume to max, you get max output from the amplifier. The signal is nice and clean, the music is dynamic and exciting and there’s no smoke! Each little turn of the volume knob results in a slightly louder system allowing you to dial it in exactly how you want it in 1/40th increments and when you want silence, you get silence, with no background hiss. Your amplifier loves you, your speakers love you and most importantly, the guy in the car next to you at the stop light loves you!
“So, all I have to do is turn the gain to the 2 mark if I have a 2 volt deck, or the 4 mark for a 4 volt deck?” It sure would be nice if it were that easy wouldn’t it? While that will get you close, it assumes two things. First, that your radio will actually do its stated power output cleanly and that you know which volume level that is at. Secondly, that all music is recorded at the same level of output. Well, you know what they say about assumptions! Stay tuned…
