The noise floor turns up with the desired signal. You get a very high signal-to-noise ratio. Starting with your acoustic treatment , then microphone, and then preamp, you can control your desirable signal while maintaining a minimal amount of noise through gain staging.
That's part of the job of a recording engineer. So back to it. Transparency is created through solid state electronics, but old preamplifiers used tube technology just like cathode ray tube televisions did. Some newer solid state pre's use transformers. Pre's that use transformers and vacuum tubes are designed to raise your signals volume while imparting a specific Color. Coloration, Color, Flavor What happens is a very pleasant distortion is applied to the signal.
This is a harmonic distortion based on the signal itself at very low volumes and lower frequencies that provide a sense of "warmness" to the signal. Manufacturers have mastered the art of creating transparent preamps not that they all are willing to spend the money on the right electronic parts to do it.
The big boys that already have their transparent models are also providing colorful models. If you're out looking to buy the best mic preamp possible and encounter the conversation about coloration, don't worry about it at all. Worry about base quality first. At the top level, flavors are just very similar and very subtle preferences for people to argue about us studio engineers have learned to hear every peculiarity! Most preamps have two types of inputs.
The main one is the XLR input that accepts the cable that runs from your microphone and the other is a TRS input that accepts the cable that runs from your electric instrument keyboard, guitar, bass, etc. You'll see the second kind labeled as "Instrument" or "Hi-Z," with the second label being an abbreviation for "high impedance. You can't just plug in your mic or instrument and magically you're at the right volume.
You need to perform gain staging. Each piece of studio equipment expects to receive a signal coming in at a certain level and that includes preamps, compressors, EQ's, and most importantly your analog-to-digital converters. This is what the Gain knob is for. Gain is the ratio of your output to your input. So the higher you turn the gain knob, the louder your volume becomes.
This is you telling the preamp how high the signal needs to be boosted. Some pre's have lights that show you what level you're operating at, otherwise you need to monitor your levels inside of your DAW. You'll also see knobs called Trim which is essentially the same thing as Gain. There are a few other switches, buttons, and knobs you'll see.
On solid state preamps with transformers and on vacuum tube preamps you'll often find an impedance knob. This changes the amount of harmonic distortion your signal will receive, which is the pleasant color saturation we talked about above. Some don't give you this option. It's pretty subtle either way. Finally, you'll see buttons for things like Invert, which just flips the phase of the signal.
This is helpful when you're recording a stereo signal like a double-mic'd acoustic guitar and you're getting constructive or deconstructive phase issues. You'll invert either the left or right channel and that typically solves it. You'll see the ability to deliver 48 volts of phantom power as well.
A lot of mics need this and the preamp delivers it. Some microphones have their own built-in or external power source though, so in that case you'd turn off the phantom power. If you're unfamiliar with different outboard studio gear, you'll wonder why so many different preamplifiers have various shapes.
Some are weird shaped boxes that sit on your desktop, while others are long and horizontal that get mounted into a rack of other equipment. Then you have the lunchbox that accepts Series shaped equipment, which can be racked or sit on your desk!
Above is a single channel desktop preamp. There are lots of musicians, such as rappers or singers who only need one high quality channel for their vocals. They don't end up with a lot of other equipment other than a preamp and a mic, so they are happy to have it sit right there on their desk. The preamplifier thus became a fixture in the highest-end equipment, an arrangement which continues to this day.
While the preamp persists as much from custom as from practicality, there is still a method in this madness. While it is certainly possible today to assemble a system without a preamp, there is still a need for one in many, if not most, applications. Ignoring for now the question of integrated amplifiers and receivers, which combine in a single chassis a preamp, power amp, and, in the case of the receiver, a tuner a more practical arrangement with today's solid-state circuits than with yesterday's tubes , the justification for a separate preamp is today based on issues of gain and impedance incompatibility.
No one will argue that passive attenuation and switching avoids the perhaps unnecessary complication of a preamp-with-gain. The simpler the better, the philosophy goes. Devices for performing this function, known as passive attenuators, or the more appropriately descriptive but nonsensical "passive preamps," have carved out a small niche in the marketplace. But they are not appropriate in all applications.
There is no widely adhered-to standard for line-level output voltage or line-level input sensitivity. While many line sources—CD players especially—will easily drive many power amplifiers to their maximum outputs, there are situations in which you won't quite be able to get the level you desire from the system.
I have encountered this with two different "passive" preamps. A preamp with at least a moderate amount of gain will solve this problem, assuming that the amps and loudspeakers are up to the user's demands. Impedance compatibility is the relationship between the output impedance of the source and the input impedance of the amplifier it is driving. This more complex problem is not unrelated to the gain dilemma described above. It is generally not desirable for the two impedances to be identical, though such a matching might be intuitively appropriate.
In fact, if the output impedance of the source is too close in value to the input impedance of the amplifier it is driving, demands may be made on the source for more current than it was designed to deliver, with a resulting increase in distortion. There will also be a decrease in effective gain as the voltage-divider effect takes place and more of the available source voltage is wasted across the source or output impedance instead of across the input of the power amp, where it is needed.
The situation is actually even more complicated than this; increased current demands may cause the source voltage output to sag. The system may also become more sensitive to the cable used to connect the source and amp in this situation.
An input impedance ten times that of the output impedance of the preceding component is commonly considered a reasonable figure to aim for. Though this is not universally accepted, it will generally minimize such impedance interactions footnote 2. The impedances of many, perhaps most, of today's sources do match up reasonably well with those of most modern amplifiers. But not all. If this isn't enough to be concerned with, the varying resistance of the system's level control, whether incorporated in the source or in a passive attenuator you'll need some way of setting gain , also enters the picture.
This level control may be buffered footnote 3 , as in the variable outputs of some CD players and such devices as Corey Greenberg's buffered passive preamp , but in truly "passive" preamps it is not.
In addition to gain, an active preamp generally provides a consistent, and low, output impedance independent of the level control setting, relieving these concerns. In the real world, of course, not all preamps are equally successful at all of these tasks. It simply isn't possible to completely ignore, as I was asked to do for the sake of this discussion, such convenience functions as switching. If you have more than one input, you do require switching of some sort—unless you actually enjoy plugging and unplugging inputs.
And for those audiophiles who still value vinyl, how can I ignore the LP preamplification stage, which is still most conveniently incorporated into a "preamp"?
The switching, of course, can be done by a "passive" preamp, with the above concerns still applicable. But a phono stage requires a more active approach. Here is yet another example of the division of functions. The rise of CD has forced many preamp manufacturers to delete phono stages and, in many cases, market the latter as separate components to those who require them.
Again, in the right system, you may be able to get along without a "preamp. An external preamp may improve your sound quality significantly, if you work with low output dynamic microphones, including ribbons. With high output condenser mics, an external preamp makes less of a difference.
Why Do I Need a Preamp? Two sought-after Neumann Vb preamp modules from the early s. Better sound quality: This becomes most evident at higher gain settings. High quality external preamps are equipped with more sophisticated circuitry that retains full transparency even at their highest gain settings. More gain: The built-in preamps of an audio interface rarely offer more than 60 dB gain, often less.
Low output dynamic mics, such as ribbons, may require up to 70 dB, sometimes even more. A special sound character: This is perhaps the most common reason to buy an external preamp.
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