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A preamplifier is used in audio production when a sound source isn't quite loud enough to work with or there is not enough signal level. I choose to boost, or amplify, the signal level to an optimal input level so that there's enough there to work with. It gives your digital audio interface enough sound to digitize and sample and take advantage of all the bit depth. It makes audio easier to work with. We want to get things up to a certain level so that the volumes are all even, and there's enough of it there to look at and deal with. Microphones and record players almost always require a preamp to deliver enough signal to be able to record, especially in today's digital audio world.
Now you can use a preamplifier to increase the gain of any single, but it's not always a first choice, and things like microphones that don't have volume knobs and record players where there's just an output, and you have to go with it, it makes sense. But sometimes a preamp can add some noise. So if you're using like a drum machine, or a synthesizer, it's better to try and turn that device volume up first and get as much signal out of that device before you start to use a preamp to get more signal. A mistake is to have things come up kind of quiet and then crank the preamp, especially if you're using preamps on a less expensive device where the preamps they're actually adding to the some of the sonic character of the signal and they're changing a little bit of the tonality of it.
So it's good to use as much of the original signal as possible. On a lot of digital audio interfaces you'll find preamps, you might find one or two, or you might find as many as eight. You can also find them as stand-alone units, and you can find nice little hundred dollar tube preamps to two-channel something like that, or you can spend a couple of thousand dollars on one single preamp. That's because, generally speaking, to the pros they're thought of as one of the most important keys in the signal flow in terms of getting good sound. If you have a great microphone and not a great preamp a lot of times you're cheating the microphone from achieving all that it's capable of.
Amps and preamplifiers fall under few different categories, or classes, based on their design. I just want to take a minute to talk about and hip you to Class A preamplifiers, because I know when you're out shopping you're looking online for different devices and gear, you'll see this distinction, and I want you to know what it means. By design the Class A amplifier is always moving current at its inputs and outputs. So when the sound arrives at an input, it immediately is on its way through the circuitry and to the output. Other amplifiers kind of have to get it in gear before that happens.
Now this happens faster than we can imagine, but the result of that Class A structure where it immediately starts to move is that you get a very clean signal path with very little distortion and very little coloration. That's the advantage of a Class A preamplifier is that it's a very clean and generally accurate device. Of course, the downside is that they tend to cost quite a bit of money. But it's worth looking into if you have a really high-end microphone or if you're just aspiring for a very high-end setup, the Class A preamplifier can really help you get a nice sound. That's not to say that life won't go on without a Class A preamplifier, but there is something to be said for using a very nice preamplifier matched with a very nice microphone.
Generally speaking, Class A preamps aren't a bad thing, but regardless of the price most preamps are going to come with a similar set of features and functions. And we're going to explain those in this chapter, but the first thing I want to talk about is getting and setting the proper signal levels. So in the next movie that's what we'll look at.
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