At the most basic level, the job of a microphone preamp (often called "mic pre," "pre" or just a preamp) is to increase the gain of the signal coming from a microphone when recording. But if that's all it did, there wouldn't be any mystery or hype surrounding them, and they wouldn't range in price from cheap to extremely expensive. As different guitar amps add different characters to the sound of an electric guitar, different mic pres add different kinds of character to the tone of whatever the microphone picks up.
Sweetwater has a great preamp buying guide article that explains this concept and more far better than I will here. If you're interested in this subject, the article covers all the bases and is a must-read. I invite you to check it out. Their article states that aside from increasing the gain of the mic, the preamp is: A creative device that you can use to add color to individual tracks. As the sonic differences of individual preamps become more apparent to your ears, you can begin to see them as colors in your sound palette, using them on different tracks and in different settings to build a distinctive sound.
When I started home recording in the late 90s, I was vaguely aware that my Roland 8 track DAW had microphone preamps built into the mic inputs on the unit. They did what they were supposed to do, and I never had any trouble getting great sound out of guitar amp by just slapping an SM57 in front of the speaker cab and going straight into the board. There was clearly a preamp in there doing something good for the sound. But because I was getting good results, I never thought much about it, or worried that I needed anything more.
However, when I started interviewing name players for DRG, the concept of good mic pres kept rearing its head whenever discussions turned to the player getting great sound in the studio. For example:
From Doug Aldrich
DRG: What are the indispensable items in your home studio? Aside from the basic monitors mixers and recorder. Are there any specific things that you always like to use?
Doug: I have a couple of Neve 1073s (mic preamps) that I bought ten years ago that I like to use. They're off an English console. It's the mic preamp that was really famous back in the 70s. And as these consoles became out-dated, people would take them out of the mixer and mount them in a rack because they loved the tone of them. And these things are really desirable. And they cost a fortune. But I got a pair of them really cheap back in 82 or something. And they've tripled in price. And they're great. And my guitar's always going through that at home. I've got other mic pres too but these things just add something — like this warmth. I go straight to tape with those and bypass the mixer. Then I re-EQ it off the mixer when it's coming off tape or ProTools or whatever. And they just sound real good. It's a transistor preamp, but it's got a tone about it. It adds something that's more punchy and in-your-face.
From Dave Meniketti
DRG: Aside from the basics of your mixers, monitors, recorders and mics, what are the indispensable things in your studio? What things do you really like to use?
Dave: I guess it's the two preamplifiers I've got. They really help out a lot in getting the sound I want out of my voice and my guitar — whether it's going through analog or digital. Really, it's a straight-ahead setup. I just plug straight into the guitar and just shove a 57 beta in front of the 4x12 cabinets. Run it through a tube mic preamplifier , and there you go. That's it. (i.e. the signal goes from the mic to the preamp, then into the recorder)
DRG: What does the preamp give you that you don't get if you don't have it there.
Dave: There's a texture to certain preamplifiers. You just have to find out which one sounds best with the amplifier you're using, the room you're using. It's a chain of events where you make experiments based on, you know — I've got six or seven preamplifiers in my studio — let me just try them all — with the same microphone and the same amplifier. And now let's switch something. Let's try a different preamp or a different microphone — whatever. And I kind of went around the block for a couple of months and usually came back to the same setup I've been using for years, which is: stick a 57 in front of a 12 inch speaker, turn it on, and here we go (laughs).
DRG: So what kind of preamp is that that you're talking about.
Dave: The mic preamplifier that I like the best is a thing called a "DW Fearn" (http://www.dwfearn.com/) — and the guy just happens to make his stuff in Boston — how 'bout that! (Editor's note: Dave knows I'm in the Boston area). He's a Massachusetts guy named Doug Fearn, and he's a guy with a long white beard, and he just makes this incredibly good tube preamplification that just sounds so natural whether you're going to digital or analog. It makes the sound of the voice just where I expect it to be. And if you put the microphone in front of he guitar amp, it just does the right thing.
From Roy Z.
DRG: Let's talk a little bit about your approach to getting guitar sounds in the studio.
Roy: I'm pretty meticulous about that. I own some really nice mic preamps. Basically, my favorite guitar sounds — I have them all here. I've got Hendrix sound, the Purple sound, I've got my sound.
DRG: Please elaborate. When you say you've got those sounds . . .
Roy: Well, check it out, man. Some friends of mine — back when — bought the Rolling Stones original mobile unit!
DRG: Oh, really?
Roy: Uh-huh. And that includes the (mixing) board. Now that board pretty much recorded Zeppelin III, IV, Houses of the Holy and parts of Physical Graffiti. It recorded (Deep Purple's) Machine Head — they had it in the lyrics of Smoke on the Water ("the Rolling truck Stones thing") A lot of classic British albums (were recorded with that). Well that same board — it's a Helios board — and it was developed by some guys who worked over at Olympic studios. And Olympic is where Hendrix recorded his stuff. So imagine that I've got — that's the same circuitry and everything. The same mic preamp.
DRG: You have the preamps from in the board?
Roy: A board is 24 or 48 strips or modules, right? Well I have two modules from the original Rolling Stones mobile. So if I want to get the When the Levee Breaks sound for the drums, I put up two room mics, and boom-bop — there it is.
From Steve Lukather
DRG: What would you consider the indispensable items in your studio?
Luke: Talent! (laughs) It's fucking true, man! Ok . . . A good set of mics, good compressors, good mic preamps and a set of monitors you can know and rely on. And if you don't engineer yourself, a great engineer who knows how to get a great sound quickly.
Conversations like these fired my curiousity and got me doing some research. The homerecording.com forum is one great resource. If you join, you can do a search on the many threads. You can also just google "microphone preamps" and find many articles. What I found is the following:
1. The interface devices that sit between your mics/instruments and your computer contain some kind of basic mic pre that does the most basic job of increasing the gain of the signal. If you have an inexpensive interface, you have an inexpensive mic pre. If you spend more on the interface, you're either getting more channels, better preamps, or maybe both. (and if you have a separate/external/better mic pre, you can/should bypass the pre that's built in to the interface device by setting it to line level. That is, let it just act as an interface, and let the better preamp color your signal.)
2. There are finally a lot of budget preamps on the market. You can get in the game for less than $100, and you can find recommendations for decent home recording pres in the $300-$500 range.
3. Real good mic pres tend to be quite expensive, and the low end ones are kind of hit or miss. Everything I've read from experienced pros suggests it's best to just save up and get the best one you can afford -- that they are worth the investment if you're serious. So my research was matching what the players were saying: the mic preamp is one of the places you should invest rather than skimp.
All of this information cemented the idea in my head that when I returned to home recording -- particularly on a computer based system, I was going to get the best mic pre I could afford.
Tube vs Solid State
As Dino guitarists, we inherrantly know that tubes seem like a good idea for adding tonal warmth to a signal. However, it is interesting to note that the classic studio preamps like the Neves (and their clones) that go for thousands of dollars, are transistor preamps. So this is a case where tubes aren't necessarily the best thing.
The Kelly Industries website broke down the differences as follows:
There are basically two types of mic preamps but there is also some that go around the definition. Solid State Preamps use either transistors or op amps (small integrated circuits with a number of transistors) to amplify the audio signal. These are generally meant to be more transparent or clean than a tube preamp. Solid State preamps are usually more resistant to noise including their own (self-noise). Because of this transparent quality solidstate preamps can have a sterile sound to them and lack a more definitive sound that tube version.
Tube preamps on the other hand are usually more expensive especially if you are trying to get a very low noise one. Each manufacturer’s preamp has its own sound because they color the sound. The trade off here is increased noise but great tone and a more natural and musical audio compression that occurs with tubes. Many studio engineers prefer tube base preamps over solid state ones but it really a matter of apples and oranges.
There are some preamps that use a solid state preamp stage and then pass the signal through a tube. The tube circuit has a drive knob that allows you to add more or less of the tube sound. This technically speaking is a solid state preamp.
Today there are many makers of mic preamps. This is similar to number of high end guitar amp manufacturers where each one offers something a bit different. The cost of some of these preamps is somewhat excessive for the average musician which puts them out of reach for most musicians.
Which mic pre is right for you?
Tough question. Just like which guitar, amp, pick, or string gage is right for you. It's largely a matter of personal preference and what you can afford.
However, that statement is hardly helpful. I would start with thinking about what you are trying to do, and how you are trying to achieve it. For example: how many channels do you need to record at once? What are you trying to record? How many of these things need a great mic pre? Here's one hint: Recording vocals is one place where the better preamps really seem to make a big difference.
Again, the Sweetwater article discusses these issues in a tangible way:
"Now, giving complete consideration to budget reality, adding a preamp to a modest gear setup can greatly broaden your studio's range. Consider the following:
- One high-quality preamp can make your low- or mid-priced mixer much more effective. In the world of project studios, the explosion of available mixers (analog and digital) and audio interfaces has been wonderful, but often these devices compromise on critical components to maintain moderate prices. You can alleviate the sonic compromise by adding a good vocal preamp that bypasses your low-cost mixer's input stage and create a noticeable improvement in the quality of your mixes.
- A variety of (even modestly priced) outboard preamps can give you more sonic tools for vocals, guitars and other instruments. Again, the different sonic qualities of different units come into play as you choose the most appropriate preamp for each track or group. With this point in mind, let's look at some specific applications for outboard preamps:
- Vocal tracking: The human voice is one of the most complex musical instruments to record, and no two are alike! While pro recording engineers strive for accuracy in most other tracks, they are most likely to choose a preamp with clearly identifiable sonic character to capture and enhance a vocal track. This often means a tube preamp with a "warm" midrange (caused by slight harmonic distortion that's a normal part of tube operation) and "smooth" high frequencies (a result of mild low pass filtering caused again by the tubes' performance). Here's where a preamp like the Universal Audio 610 or 2-610 really shine, but even economy-priced units such as the PreSonus TubePre can add "tube sound' to your arsenal.
Vocals are an area where recording engineers also opt for channel strips, which are a combination of preamp/compressor/equalizer in one box. Units like the Vintech X73i (a recreation of a Rupert Neve design) or the dbx 376 are examples. - Guitar/keyboard amps and direct injection: guitar amps can be a challenge to record due to their inherent distortion and high SPLs. Here's where a preamp with a wide dynamic range and lots of headroom - input capacity without breaking up - comes into play. Similar issues appear when you're recording amplified keyboards. In both cases, many engineers prefer to record guitars, basses and electronic keyboards "direct," bypassing the speakers and using an impedance-converting DI box. To compensate from a perceived loss of presence caused by this, they often run the DI into a tube preamp to regain the "punch" that a tube's harmonic distortion provides. The bargain-priced Samson C•Com 16 Valve and the high-end Groove Tubes Vipre fit this category.
- Preamps that can handle a variety of mics: If you already own a collection of dynamic, condenser, tube, and even ribbon mics, you need a preamp that can handle the different output impedances these mics produce. An example of a variable input impedance preamp is the Avalon AD2022.
- Remote recording preamps situations: When you're going out to the venue to record, you don't want to haul racks full of different gear you might never use along. Here's where multi-channel preamps become particularly useful. Some symphony orchestras have been recorded using just a 2-channel preamp like the Amek/Neve 9098 DMA; for more mic-intensive situations a 4- or 8-channel unit such as the PreSonus M80 provides 8 inputs at a modest price.
- Vocal tracking: The human voice is one of the most complex musical instruments to record, and no two are alike! While pro recording engineers strive for accuracy in most other tracks, they are most likely to choose a preamp with clearly identifiable sonic character to capture and enhance a vocal track. This often means a tube preamp with a "warm" midrange (caused by slight harmonic distortion that's a normal part of tube operation) and "smooth" high frequencies (a result of mild low pass filtering caused again by the tubes' performance). Here's where a preamp like the Universal Audio 610 or 2-610 really shine, but even economy-priced units such as the PreSonus TubePre can add "tube sound' to your arsenal.
So, there's a method to building a collection of preamps that fill your different recording needs. The most important thing you can do is clearly define your applications and your recording plans: what are you recording, now and in the future? Now ask the hard question: what's your budget? When you've answered both, you can begin to select the appropriate preamps that answer both questions."
Here is another good buying guide from Musician's Friend.
My own personal conclusion
Had my only need been to record loud electric guitars by micing a speaker with an SM57, I probably would have gone for something at the budget end of the spectrum. More experienced home recording engineers that I know and trust have said good things about the PreSonus products, and I might have gone that route.
However, one of my needs is to record vocals at a high/pro level. However, since I rarely need to record more than one track at a time, I chose the Vintech X73i, which is a solid state, one-channel modern clone of the classic Neve 1073 (which includes EQ functionality), at what everyone says is an "affordable" price (around $1500 with the required power supply). This unit has gotten some rave reviews and real good press. In a couple of shootouts with real Neve's, several experts couldn't tell the difference. I was told it was pretty much impossible to get a bad sound out of it. This preamp should work great for recording vocals or acoustic guitar with a condenser mic, or even a mic'd amp or direct guitar. The other preamps I was looking at were even more expensive Neve clones.
Later on, I added another pre. A Chandler TG-2, which is two channel preamp (no EQ) that has a very good rep for recording guitars, among other things. It has a very simple interface that just lets you adjust the signal's input and ouput, and it is pretty different in character from the Vintech. It's analogus to adding a different guitar or amp to your arsenal. You do it to have a different sound.