Buying Guide:Preamps Buying Guide
- 1. How To Use This Guide
- 2. What is a Preamp and What Does it Do?
- 3. Do You Need a Preamp if You Have a Mixer or Audio Interface?
- 4. "Color" vs. Transparent Preamps
- 5. Preamp Types by Circuit Design
- 6. What is a Channel Strip?
- 7. Transformerless/Transformer–Coupled
- 8. Understanding Applications > Intelligent Selection
- 9. Should You Buy a Preamp or Channel Strip?
- 10. The Benefits of Owning More than One Preamp
- 11. Applications for Different Types of Preamps
- 12. Should You Choose Mono, Stereo, or Multi-Channel?
- 13. Preamp I/O
- 14. Preamp Features
- 15. What Do the Specs Mean?
- 16. Choosing a Preamp — What to Look For
You’ll no doubt notice that this buying guide is quite long. In reality, it’s quite short in relation to the numerous books and articles written on the subject. To accommodate your needs as best as possible, we’ve created three ways of navigating this guide (four if you count clicking through the table of contents).
First, for those who subscribe to the philosophy, “when in doubt, know everything,” just read through from beginning to end and check out the sidebars along the way. Second, for those who want more of an overview and basic insights, we have the Fast Track. Just start reading and along the way you’ll find the icon at paragraph headings or in the body of text. This will permit you to click through the important issues of preamp selection without reading all of the details. Of course, there’s no reason why you can’t stop, view more details, then jump back on the Fast Track. Third, we have the Faster Than Light Drive , which takes you straight to a list of preamps and their applications without any of the theory.
You Need To Ask Yourself a Question . . .
Before you can decide which preamp or channel strip is best suited to your musical vision, you have to ask yourself a question: Do I feel lucky? (Sorry, having a Clint moment there…) Actually there are a number of questions you need to ask yourself, which should take luck out of the equation, that is, once you know your options. So, before you sit at the feet of Swami Snatch-your-dineros, audio guru extraordinaire, or listen to countless assertions without proof, we’ve designed this buying guide to provide insights, answers, and a little history about what happens on the other side of the glass — and while a little techno-babble is good for the soul, we’ve also set about the task of demystifying and clarifying the specs and jargon, because sometimes the big numbers don’t necessarily mean better sound.
Remember that there are near infinite paths to audio nirvana. A little knowledge will take you a long way, but in the final analysis, it will be your ears and budget that will determine which path you end up taking.
You’ve heard the term pre-school? Basically, it takes a low-level intelligence (a person whose last job description was “Embryo”) and brings them up to spec in order to attend regular school. A preamplifier does much the same thing to audio signals before they go to a power amp or recording equipment.
In essence, the preamp’s job is to take a low level signal, possibly from a guitar pickup, mic, or turntable etc, and amplify it to line level. Technically speaking, the preamp provides voltage gain but no significant gain in current. That makes a preamp good for recording applications, but if you want to actually hear the signal, a power amplifier must follow. The power amplifier provides the higher current and voltage needed to drive loudspeakers. (A guitar amp incorporates both a preamp and power amp in one housing.)
Even though preamps appear to be utilitarian devices, they also cross over into the creative realm of music in terms of the sound quality they impart to a given signal. One preamp may excel at recording guitars and vocals, while another may be better at audiophile or orchestral recording.
Preamplifiers come in various forms. They can be built as a standalone unit, or integrated into a modular system such as a recording console or standalone channel strip (see What is a Channel Strip? below). The standalone channel strip is based on the console channel strip, which combines a preamp with other signal processing circuits including EQ and compression. (More on that later.)
If you own one of today’s affordable mixers that promises performance rivaling more expensive consoles, or use an audio interface with DAW recording software and processing plug-ins, you may wonder why we would recommend buying an external preamp to record through. The answer is simple. While these mixers and interfaces have successfully brought studio recording to the masses, some corners had to be cut in order to keep the prices down. In fact, even with world-class recording consoles, in order to keep prices down, the first place manufacturers would slash and burn was in the preamp section. This is one reason why using outboard preamps became a standard practice in the studios.
Aside from that, in a console, the signal has to travel through a number of circuits, switches, amplifiers, busses, controls, patch points, etc, until it reaches the output. Each one of these detours degrades the signal to some degree, and once degraded, it cannot be restored. Recording direct from the preamp to recorder offers the clearest, most detailed, and punchiest sound. Even Mr. Rupert Neve, creator of the legendary $1.2 million Focusrite Forte mixing desk has stated that the best recording path is the simplest — from mic to pre to recorder. Besides, there just isn’t enough room in a console’s channel strip for a tube design or the sophistication of today’s external preamps. Meanwhile, it certainly stands to reason that you won’t get the same sound quality from a $3,000 mixer as you would from one costing a million, which makes the need for a good outboard preamp that much more essential. To be fair, numerous hit records have been recorded exclusively on such consoles, but today, they are more often used for mixdown and monitoring.
With digital workstations, the audio interface takes the place of the routing and monitoring functions of a mixer, and while they may contain preamps, they are usually not the focus of the unit. For professionals working with DAWs, the use of a quality analog front end bypasses the lesser preamps of the audio interface and adds character to the inherent sterility of digital recording.
The beauty of adding a high-quality preamp or channel strip to your setup is that instead of paying, $4,000 per channel times 32 for a pro-quality console, about $2,000 to $3,000 buys you a “gold channel” for your DAW or mixer that you can use to record track by track. That’s one of the secrets of having world-class sound on a project studio budget. If you need to record more simultaneous channels, there are a number of high-quality multichannel preamps available from , , , , and others.
While there are several categories of preamps in terms of circuit design, aesthetically they can be divided into two main groups. Those that impart a distinct timbral characteristic to a sound are commonly referred to as “color” preamps. Those that deliver a signal that remains as true as possible to the original source material are referred to as being “transparent.” You’ll usually find both types in most studios to meet a range of recording needs. For example, a color preamp can add body or character to a thin voice or instrument, whereas a transparent preamp strives to reproduce the sound as accurately and true to life as possible.
|Groove Tubes ViPre|
In rock and pop recording, the idea is to make the music sound larger than life, and more importantly, sound unique. This is where you’ll find more color preamps in use. The people who subscribe to this school of thought tend to be mavericks with more of an “anything goes” outlook. That is to say, whatever gives you the sound you’re looking for, whether it’s hi-fi or lo-fi, then that’s what you use. Preamps that fall into this category are generally tube and solid state, transformer-coupled designs. Examples include the , , , , and .
|Grace Designs 101|
On the other hand, there are producers and engineers engaged in audiophile recording who firmly believe transparency is the only way to go. The audiophile school believes that there should be as few active components as possible in the signal chain in order to achieve the best possible and most realistic recorded sound. To the super-tweaks, the best preamp would be a straight wire with gain. Shy of that, they seek one that offers the shortest signal path possible from input signal to recorder. Generally, these folk will prefer solid state, transformerless preamps. Such preamps are built by companies including , , and
It’s Not a Clear-Cut Case of “Us” and “Them”
Remember, transparent does not equal sterile! George Massenburg (designer and builder of equipment found in top mastering studios) is perhaps the foremost proponent of transparent equipment, yet he produced rock and pop music. His belief is that you can’t mix or EQ properly if you can’t hear the actual sounds you’ve recorded. Besides, if the instruments already sound good to begin with, then you’ll want to reproduce them as accurately as possible without electronic artifacts (or at least as few as possible). It is also possible for solid state preamps to emulate the sound of tube pres, which has been proven by the aforementioned Mr. Neve,designer Ted Fletcher, and others.
Keep in mind that electronics will always add or take away something. The only true acoustic reproduction is done by your ear. When you think about it, any sound that’s picked up by a microphone, converted to a voltage and then sent through preamp, EQ, compressor, digital converters, and ultimately out to loudspeakers is going to be affected in one way or another. As such, an audiophile recording of an acoustic guitar or grand piano by definition is actually electronic music. In the final analysis, it’s the sound that is most pleasing to your ear that matters.
Generally preamp design falls into two main categories, tube and solid state. Tube preamps, as the title implies, employ thermionic tubes (or “valves” as the Brits call them), to create gain. Tube preamps fall mainly into the “color” category and are known for their ability to add character, midrange presence, deep bass and an upper frequency response that is described most often as “open and “airy.”
In discussions regarding the desirability of tube preamps, you’ll often hear the words “warm” and “fat” used incessantly, but what do they really mean? Let us clarify. It helps if you understand how tubes function. First, as signal level increases, the tube produces mild distortion, which in turn produces the body and depth that the word “warmth” is meant to describe. Since the distortion is produced gradually in measured amounts, it is pleasing to the ear. Going deeper, the distortion itself takes the form of second- or even-order harmonics, which are considered to be more “musical.” Here’s why: Harmonics are component pitches of a fundamental tone that sound at whole number multiples of the fundamental. Musically speaking, the second-order harmonic forms the interval of a perfect octave. The octave reinforces the fundamental tone, similar to the effect known as doubling. That’s where the word “fat” comes in since octave doubling results in a broader sound with more depth. (“Beefier” is another word used to describe tube preamps by engineers and producers.) Even-order harmonics allow for pleasing distortion (much like power chords on guitar) since they don’t produce the dissonant pulsing (intermodulation) caused by odd-order harmonics. The addition of even-order distortion via tubes equals color.
Another factor that contributes to the musicality of tube designs is their natural compression characteristics. If you were to look at the output waveform of a tube preamp, the curve at the top of the wave becomes gradually compressed as more gain is applied (or the tube is overdriven). This natural compression is also more pleasing to the ear. In the mastering stages of professional recording, compressors that utilize tube compression such as the classic Fairchild 670 (which can go for $30,000 on the vintage market) are still sought after for the “audio glue” they apply to a mix, giving it that finished-record sound. Yet another natural function of tubes is to act as low-pass filters, which smoothes out distortion in the high end of the spectrum and somewhat reduces high-frequency content. This can be desirable or undesirable depending on your sonic goals in a given instance (e.g. desirable for warmer vocals, undesirable for percussion, where attack information is essential).
Solid state preamps employ transistors or op-amps to achieve gain, which do exactly what tubes do, only more efficiently and with less heat. As opposed to their tube counterparts, transistors operate more consistently as gain is applied. Solid state devices maintain very low distortion right up to their maximum level, beyond which they distort in the extreme (called clipping). This is actually a good thing since solid state amplifiers can provide excellent performance when operated at maximum gain. The result is a more accurate capture of the input signal. This is why solid state devices are called transparent. Since solid state devices will accept much larger gain increases prior to distortion than tubes, you can record hotter signals without distortion.
While tubes have achieved cult status as being more “musical” than solid state components, there are also solid state preamps that are renowned for their sonic signature, such as those made by Mr. Rupert Neve, the grandfather of pro audio. (Like the aforementioned Fairchild, vintage Neve preamps such as the 1073 still fetch many times their original price.) According to Mr. Neve, when transistors came into being, he simply thought of them as just another form of component and set about the task of understanding their characteristics in order to apply them in musical context. Apparently he was successful, as the inherent musicality of Neve gear has become legend in professional audio.
Recently, hybrid designs have emerged that combine both solid state and tube components. The transient response and clarity of solid state devices with the ability to add the rich second-order harmonics of tube saturation as seasoning.is an example. It uses solid state circuitry for the input stage with an output gain control that drives a tube. This design aims to combine the faster
|Focusrite Liquid Channel|
The latest development in preamp technology is modeling, which also employs solid state circuitry, while “warmth” and other abstract sonic qualities are added in digitally. In the case of the , convolution processing is used in conjunction with actual physical changes in the analog circuitry. The result is the ability to mimic the sound of virtually any preamp and compressor, tube, solid state, or otherwise, in any combination. While some purists feel that there is no substitute for the real thing, the Liquid Channel has found a home in many top studios. Of course, since the Liquid Channel combines both preamp and compressor models, by strict definition it’s considered a channel strip.
Basically, we’re talking about a preamp that combines analog input with A/D/A conversion and digital outputs for recording direct to a DAW, bypassing the DAW’s converters. Some preamps offer an optional digital output card that can be installed by the factory or by the user, such as the Apogee is known for making some of the best digital converters in the indus— the distinction is regarding function. Perhaps it would be more accurate to say “preamp with a built-in audio interface.”, while others feature digital conversion and output integrated into the preamp’s design, such as the and the . These preamps could also fall under the category of audio interface, however, the main focus of these units is their preamp sections. This is not to say that the digital section is of lesser quality —
Here we have a category of preamp that can also be categorized as an active DI (see the section within our DI Buying Guide.) Generally when we say “preamp” we’re really thinking “mic amp,” with an instrument input added as a secondary convenience. With the myriad tones available for electric guitar and bass, certain manufacturers have created preamps that cater specifically to the impedance requirements of these instruments without additional circuitry. For example, the , while categorized as a DI, is actually a tube preamp designed primarily for bass guitar. Many of these preamps fall under the category of modeling preamps and include guitar- or bass-oriented DSP effects that can include distortion and modulation effects, plus speaker cabinet, mic, and amp modeling. The advantage of an instrument-specific modeling preamp is that you can have the tone of a specific guitar amp manufacturer such as Marshall, available for direct recording without having to buy an entire amp and additional DI to send the amp’s output to your DAW or console. If you recall our , we stated that a guitar amp has both preamp and power amp. For examples, see .
Certain mic preamps can also be instrument specific. For example, thepreamp from the aforementioned A Designs Audio is designed to work best for miking snare drums and electric guitars. This is achieved with the selection of input and output transformers. The number of coil windings and type of wire used in the transformers will emphasize certain frequencies. For example, nickel wire brings out high frequencies. The advantage to selecting preamps such as those from the EM-Series is that the knowledge that comes from years of experience in selecting the right preamp for specific instruments is “built-in” for you.
|Trident S80 Producers Box|
Basically, you can consider any preamp with additional signal processing circuits to be a channel strip. The channel strip of today is a standalone unit that in its most common form comprises a preamp, equalizer, and compressor/limiter . Some channel strips offer variations on that theme such as preamp and EQ only, or preamp and compressor only, while others offer additional sections such as a de-esser or enhancer. In short, a channel strip can offer all the signal processing tools you need in one box.
Initially the console channel strip grew out of the need for convenience. When most recording was done in the major studios, engineers didn’t want to spend the extra time connecting various units together. Besides, with the clock ticking away at $250+ an hour, a sneeze would cost a producer about five dollars, and $50 for quick trip to the bathroom. This was the single most important reason for the birth of the home project studio. (See History of the Channel Strip sidebar.)
In terms of component use, channel strips tend to employ hybrid or solid state designs. For example, the Universal Audio 6176, while the is solid state only.combines both tube and solid state circuits, as does the
Just as some people rally round the PC flagpole and others pledge their troth to Mac, approaches to circuit design evoke similar reactions.
The reason we are singling out this particular component, or lack of it in a preamp’s circuitry is because this is mainly where the difference between color and transparency lives. Transformer-coupled designs sound beefy and tend to be punchier (often referred to as the “big iron” sound of the ’70s) than the transformerless preamps. Since all transformers color the sound of a preamp, designers in search of an uncolored, true-to-life reproduction of sound prefer to eliminate them from the circuit path.
Due to the reduction of active components in the signal path, this is a desirable design feature in the realm of transparent preamps. A transformer will always add a level of coloration to a signal, and as such, a design employing transformers cannot rival the transparency of a well-designed transformerless input, particularly in the upper range of the frequency spectrum. (We’re talking audiophile degrees here.) Transformerless designs are more prevalent in solid state preamps. Transformerless tube designs do exist but they tend to be very expensive since they are more difficult to build than their solid state counterparts. Major proponents of transformerless design are John La Grou (Millennia Media and George Massenburg (GML).
Benefits of Transformers
As we said in the introduction, the function of a preamp is to take a low-level signal and increase it to line level. The function of a transformer is to bridge the input section of the preamp to the output section while increasing signal voltage. The transformer does this by virtue of magnetic coupling. Because there is no hard wiring between input and output thanks to the transformer’s magnetic coupling, they offer better circuit protection and the benefit of true electronic isolation, which results in minimal noise or hum when connected with other equipment. So you see, they’re not all bad. In fact, certain classic solid state transformer designs are still highly sought after for the coloration they impart and command quite a price on the vintage market. The important issue in a transformer-coupled design is the quality of the transformer, which is why manufacturers such as and PreSonus (for the have them custom made.
As you can see, there are no absolutes. Electronics is a study in tradeoffs. There’s no reason to reject one design or another out of hand based on design theory. We suggest you listen to examples of both designs and see what your ears tell you. If you like the sound of a particular preamp, whether or not it uses transformers becomes irrelevant. It’s much like choosing a guitar. If you want a Les Paul, you simply accept that is has a set-in neck even if you prefer a bolt-on neck. Conversely, if you think that a set neck is superior, but want the sound of a Fender Stratocaster, then you accept the bolt-on neck.
Hopefully by now, you have an idea regarding which type of preamp you may wish to select, but for those on the fast track, lets just get right into to the meat of the issue and discuss the advantages and applications of tube and solid state devices. This should help narrow it down for you.
|Tube-Tech MP 1A|
When character, body, or a thicker sonority is required, particularly when vocals or instruments are thin sounding, a tube pre does the trick. If for artistic reasons, you want a thicker sonority for instruments in general (wall-of-sound rock guitar, bass, string samples, synth pads, violin, etc.) the tube preamp is a good choice here as well. Examples include the,
When is “analog warmth” too much? If you’re recording instruments that are already rich in the midrange and lower midrange, without a prominent attack, you might find that a tube pre can cause the sound to be a little too thick. Since we take spatial information from highs, the tube pre’s natural tendency to act as a low-pass filter, smoothing or reducing high frequency information might make an instrument already lacking in high-frequency content sound a little smeared or indistinct in its placement in the stereo field. Conversely, a tube preamp can also be used to tame sounds that are too prominent in the high-frequency range. A well-designed tube preamp can also sound open and “airy” in the high registers, so again, nothing is written in stone. Do not, however, expect a tube preamp to be as quiet as its solid state counterpart, as tubes emit more thermal energy, which translates to noise.
Since solid state preamps have a faster transient response and better high-frequency response (this is where instrument attack and spatial information lives), you’ll most likely want to use them on drum overheads and instruments with percussive attacks (piano, acoustic guitar, etc.). Basically, in any application where you want more detail and transparency, the solid state preamp will be your best friend. You can also use them to effectively bring out instruments or vocals in a mix that are dull and lack detail. (While tube preamps can be detailed and accurate in the highs, this is generally where solid state rules.) If you want transparent audiophile-quality recording, a high-quality, transformerless solid state preamp such as the are excellent choices.
It is important to keep in mind that solid state preamps are not limited to transparency. Certain solid state, transformer-coupled preamps are also capable of producing a rich, colorful sound. Examples would be the, , and the .
If you are unable to afford both a tube and solid state preamp, you might do well to consider a hybrid design, such as the. It combines solid state input circuitry with an adjustable gain tube output, which enables you to add some second-order harmonics to the signal. Another possibility would be the channel strip, which offers a choice between tube and solid state, transformer-coupled, or transformerless operation in virtually every audio function. While it’s more expensive than the Summit 2BA-221, it’s one investment that may well cover all your recording needs for a long time to come. Of course, to most recording engineers and producers, preamps are like potato chips — nobody can have just one. For those who prefer numerous tonal options in their palette of audio colors but can’t afford a vintage outboard gear museum, a modeling channel strip such as the is the next best thing.
Channel strips offer certain practical advantages including convenience and cost effectiveness. With your signal processing tools all in one box, you don’t have to spend time setting up and patching separate components together. (This is the concept behind the recording console, from which channel strips are taken.) Let’s say you’re recording vocals. Normally you’d use a preamp, a compressor and a de-esser. Rather than buy three separate units, a channel strip can give you all of those functions in a single box for much less than it would cost to buy the units separately. On top of that, say you want the British rock sound of a Trident console or SSL desk, then buying a channel strip such as the or the is just what the producer ordered.
On the other hand, if you’re recording acoustic instruments or orchestral ensembles where accuracy and detail are essential, a channel strip might not be your first choice. Those engaged in audiophile recording would likely select a preamp with no other devices or circuits in the signal path for the cleanest possible acoustic reproduction. That concept also holds true for pop music. Additionally, using a preamp alone allows you to save other signal processing for mixdown. For example, if you record vocals or instruments with EQ applied, the sound, which may have been great on its own, might not sit well in the final mix. You may find yourself trying to cut the very frequencies that you originally boosted. The same applies to compression, reverb, delay, and other effects. That’s why engineers tend to save those types of signal processing until the mixdown process.
Another factor to consider is noise. Since all of the signal-processing sections of a channel strip are combined in one matched unit, the chances for self-noise and hum from ground loops are minimized as opposed to the greater possibilities for noise that may occur by combining separate units from different manufacturers. But there’s another side to that coin. By using a preamp only and saving signal processing for mixdown, the ground loop issue is negated. It may also be argued that compared to a preamp, a channel strip will have more noise along with some signal degradation as audio passes though each processing section, even if they are unused. With that perspective in mind, some channel strips, such asallow you to use the preamp or EQ sections independently of one another, taking an output before the unused component for the shortest possible signal path to the recorder.
Since 24-bit recording enables the engineer to be less concerned over recording levels (see our Buying Guidefor more information), many prefer to record without compression. In this case, going direct from the preamp will provide the cleanest possible signal path. Once in the digital environment, additional signal processing can be done with plug-in emulations of outboard signal processors.
Some engineers prefer to record vocals with mild compression. In that case, wouldn’t it make sense to use a channel strip? Yes, provided you like the sound of the channel strip and that it works well with the singer’s voice. But what if it doesn’t? Having different preamps allows you to find the one that’s best suited to the source material. The advantage of separate components over a channel strip is the ability to mix and match different units for unique sounds, specific purposes, or to use them individually to process already recorded tracks. For example, many engineers prefer to use one particular compressor or EQ with different preamps. More importantly, certain signal processors have become industry standards for the sound they impart to vocals, guitars, or drums. For example, the and have been studio standards for decades on vocals and drums respectively. In other applications, you may find that an all-tube compressor is absolutely magical when combined with a particular solid state preamp, and a dismal failure when combined with another tube preamp (hypothetically speaking). Going back to the analogy of the guitar, a Les Paul will sound differently when played through a Marshall stack as opposed to a Fender Twin Reverb combo amp. Your choice depends on the requirements of the music. The same concept holds true for preamps and signal processing equipment.
To sum up, by offering both preamp and signal processing in a single unit, a channel strip is convenient, cost effective, and can offer the “signature” sound of a coveted console. The advantage of a preamp is that if provides shortest signal path to a recorder and the ability to mix and match them with other processors for unique sounds, specific recording purposes, and the possibility of creating your own signature sound. Ultimately, your application will determine which you use in a given setting. Sometimes, you may want to use a preamp and nothing else (say for recording acoustic guitar) while at other times, the channel strip will provide precisely what you need (recording vocals, for example). Finally, if your budget doesn’t allow for separate components, start with the best channel strip you can afford. If you just need to get a signal into a recorder or DAW and plan on processing digitally, get the best preamp you can afford.
Mics respond differently when matched to different preamps. This is mainly due to loading and gain characteristics unique to each preamp. Each possible combination of mic, preamp, and source material offers its own unique sonic possibilities (some good, some not so good, some absolutely magical). The near limitless sonic possibilities are a primary reason why outboard gear has become so popular among the more creative engineers and producers. Also, from reading the above applications, it becomes obvious that a good studio should have both colored and transparent preamps.
For example, you may be recording a singer/acoustic guitarist whose voice is a bit thin. You could add a little body to the voice with a color preamp (tube) such as a midrange. You wouldn’t necessarily want to add more harmonic content, as it may muddy the sound of the guitar. A transparent preamp with excellent transient response such as a or (both solid state tranformerless) may be just what the doctor ordered. Creative engineers and producers think of each preamp and mic combination as another color with which to paint a sonic landscape. For a painter, one color is a blank canvas. Fortunately, there’s the advantage of instruments providing their own distinct sonic image, so until you can afford a rack of preamps, you can get by. However, if you only “paint” in one color, you lose the contrast and variation that gives a mix dimension and a life of its own. Plus, if all you own is a color preamp, you may find that your recordings suffer from too much color.or a . For the acoustic guitar, let’s assume that it has a mahogany body, which would make it rich in the
If you can’t afford more than one preamp, or don’t see yourself owning more than one (just wait, you’ll get bitten by the gear bug soon enough!) a preamp with “tone” switches such as theand can offer enough tonal variation to keep your recordings interesting.
(Fast Track users, select appropriate category and continue at section 13.)
|Universal Audio 2-610|
If you’re just going to record yourself (or a guest artist) one track at a time, then a mono unit will suffice. For example, if you’re a guitarist-vocalist whose backing tracks will be created virtually via sample players, virtual synths, or audio loops, you’ll only need one channel. Keep in mind that if you wish to add a little sonic spice to stereo keyboards, or record your amp or acoustic guitar in stereo for some spatiality, you might consider a 2-channel or stereo preamp/channel strip. Even virtual instruments or stereo samples could benefit via re-amping through a 2-channel or stereo preamp. Besides, better more than less, we always say.
Will You Be Recording Multiple Tracks Simultaneously — Studio or Remote? (If not, get on the Fast Track)
|True System P-Solo|
If you plan on recording miked drums, rhythm sections, horn sections, or full bands, then you’ll need a multichannel preamp. There are a number of rackmountable 4- and 8-channel preamps such as those made by, , , , , and . If you are doing location recording and need more than eight preamp inputs, certain 8-channel units such as those by or can be cascaded or expanded to offer more input channels. For those who can’t settle on a fixed number of channels, some manufacturers have come up with a clever solution in the form of application-specific single-channel preamps, such as the , that can be cascaded in groups of up to eight in specially-designed open racks. This offers a great solution for a growing studio. As your need for channels increases, you can add preamps as you go.
If you don’t plan to do remote recording but would like to expand your DAW’s capability to handle more simultaneous microphone inputs, a multichannel preamp would be a welcome addition. For example, if you own a Digidesign Digi 002 and would like more mic inputs, an 8-channel preamp with an ADAT lightpipe or FireWire output is just the ticket. Examples would be the , the , and the
An integral part of preamp selection is to know what type of input and output connectors you’ll need. A combination of XLR and 1/4" outputs will pretty much take care of most input configuration you’ll come up against. Some preamps also have digital outputs or option cards for digital output, but then we tread into the realm of digital audio interfaces. For this guide, we’re going to keep everything analog — nice and simple. (See our buying guide for more information about audio interfaces.)
Balanced and Unbalanced
Balanced I/O is generally preferred, particularly in high-end preamps, due to its noise canceling properties. In some cases, you will find unbalanced inputs and outputs in pro equipment. They are used mainly for instrument inputs, effects loops (which allow you to send to other signal processors), and outputs that mirror the main outputs for connection to mixers or audio interfaces (used for zero-latencymonitoring with DAWs). Unbalanced cables can be used with balanced I/O without problems, provided that the length of the cable is relatively short. With longer cables you’ll want to go balanced. Overall, your best bet for a noise-free system is to go with all balanced I/O.
Most preamps offer a back-panel switch that allows you to select between these two operating levels. These are the voltages that have been determined for consumer (-10dBV) and professional gear (+4dBu ) to operate for optimal performance. The main difference between the two is that the +4dBu operating level of professional equipment provides more headroom and allows for longer cable runs without signal degradation. As a result, power supplies for professional equipment are much more expensive. In properly designed equipment, there is no appreciable difference in sound quality between –10dBV and +4dBu systems — unless you are trying to use very long cable runs at the –10dBV setting.
All of your equipment should be set to the same operating level. If you’ve set your system to operate at +4dBu and you have a unit that only outputs at –10dBV, that’s where the switch comes in handy. Otherwise, you may find that you don’t have enough gain. Conversely, if you try to send a +4dBu output into a -10dBV input, you’re going to have overload and distortion problems.
Digital outputs on preamps (usually provided by digital option cards), come in a number of varieties. AES/EBU is a professional standard that can take the form of 3-pronged circular XLR jacks or 9-pin connectors ( ). S/PDIF Sony/Phillips Digital Interface), which can take the form of a typical RCA connector connector or optical port, is generally considered to be a consumer format. Keep in mind that AES and S/PDIF refer to a data transmission scheme, which is why the hardware can take different forms. For example, on the Focusrite ISA 428 digital option, the 9-pin AES format can be switched to S/PDIF. ADAT lightpipe, an optical format developed by Alesis, can transmit eight channels of audio. TDIF (TASCAM Digital Interface) can share the same format as ADAT, but only transmits two channels. TDIF also comes in a 25-pin form (D-sub), which can be found on the . Some digital preamps also have FireWire outputs, such as the , which features eight preamps, but this is where the line between preamp and audio interface begins to blur. Another type of digital I/O to be found on preamps are BNC connectors that transmit digital clock information (Word Clock). Again, this falls more in the realm of audio interfaces.
Below you’ll find some of the most common features found in preamps. Keep in mind that certain features may be necessary, while there are others that you may occasionally or never need (usually there’s a workaround for those.) Rather than go for an extensive features list, you might want to sink more of your dollars into sound quality. Certain manufacturers take this into account when they design and leave out features that by virtue of their position in the signal path may compromise sound slightly. To some preamp makers, the features are the specs, but in this guide, we choose to separate the two since not all specs determine sonic performance.
The classic example used to explain impedance is to think of water flowing through a hose with a nozzle. With the nozzle wide-open or completely removed (low impedance), water flows freely, but with less force. As the nozzle is closed blocking the flow of water (higher impedance) resistance to the water stream is increased resulting in more force accompanied by a hissing sound (high frequency). In terms of a mic connected to a preamp, higher input impedance means greater maximum output for the mic and more high-frequency content. It also reduces distortion and provides noticeable improvement in transparency. A basic rule of thumb is to make sure that the preamp’s input impedance is at least five times higher than the mic’s output impedance. Variable impedance lets you dial high-frequency content up or down, as you desire. This serves two purposes. First is the ability to EQ your input signal without adding another unit into the signal chain, thus maintaining a purer signal. Second, you can improve the performance of your mic by increasing the preamp’s input impedance. One reason for this is because microphones exhibit different output impedances at different frequencies. The higher the input impedance, the less effect the variations in output impedance will have on sonic quality.
This is an area where your “winging-it” and Fast Track privileges are suspended. In conventional DC-Polarized condenser mics, phantom power supplies the voltage required to polarize the mic’s transducer element (capsule). It is called “phantom” power because the supply voltage is effectively invisible to any balanced microphone. Phantom power supplies the voltage through microphone cables to power condenser mics, so if you plan on using a condenser, the question of whether or not you need it is already answered. Beyond that, you need to know if a preamp’s phantom power supplies the correct amount of voltage and enough current for your mic. Most condenser microphones require phantom power in the range of 12-48 volts DC, with many extending the range to 9-52 volts DC. Contrary to popular myth, increasing the phantom power does not improve sound quality. The mic’s electronics never “see” the voltage direct from phantom power, but there are exceptions. For safety’s sake, just stick with the recommendations by the mic’s manufacturer.
Phase Reverse/Polarity Reverse Switch — What Is It, Do You Need It?
This switch can be handy if you’re working with multiple mic setups as far as checking for phase cancellation or improperly wired mic cables. If you’re just going to record with one mic at a time, then you won’t need it. On the other hand if you plan on using your preamp’s DI to record a direct signal along with a miked signal (such as a bass), then a phase reversal switch is necessary. Phase reverse is actually a bit of a misnomer, but we’ll use it since it has become an accepted term. This is a topic that causes a bit of confusion since a signal that is 180 degrees out of phase can appear to be the same as a signal whose polarity is reversed. Phase is a time-related phenomenon that can only be measured when two signals are present (AC) whereas polarity is the simple reversal of positive to negative in one signal (DC). On a preamp or mixing console, the switch actually reverses polarity. Its function is to correct 3-pin XLR (balanced) cables that are wired backwards (pin 2 & 3 are cross-wired). While this can be a useful feature for stereo recording, a phase switch in the signal path will add some coloration to the signal. Hence, audiophile enthusiasts may prefer a preamp without it. If you subscribe to the transparent school of recording and require a polarity reverse, simply wire a cable “backwards” (swap pins 2 and 3 on one end of the cable) and put some red tape on it — vo— instant polarity reverse without adding switches to the signal path.
If you have a high-voltage input signal that’s causing your preamp to distort, a pad will attenuate or reduce the signal to manageable levels. Of course using a pad means a tradeoff in signal to noise ratio, but in anything shy of audiophile recording it’s not terribly significant.
DI — Hi-Z Instrument Input
Many preamps offer a convenient front-panel 1/4" input for direct recording of a guitar, bass, or other instrument. This feature is particularly useful for a number of situations, such as combining a miked bass cabinet with direct sound or processing a clean guitar signal with plug-ins. Certain high-end preamps don’t offer a DI since it is difficult to get circuits designed to operate at +4dBu to handle the lower power requirements of unbalanced instruments. Many engineers prefer a high quality, dedicated DI for instruments. (See our )
This allows you to combine or link (cascade) two mono preamps or channel strips into a stereo or multi-channel setup. This is a good feature if you have a mono preamp or channel strip you really like and want to add more of the same model to your studio as budget allows. It also provides the opportunity to add multi-channel or stereo signal processing as you go (with similarly equipped units). Examples would be Summit’sand or the (channel strip), which includes signal processing. Chaining gives you the capabilities to perform stereo recording or mastering to a final two-track mix.
Gain control: stepped vs. infinite.
Gain controls are either infinite or stepped (also known as a stepped attenuator). A stepped attenuator lets you come back to an exact setting. This is particularly useful for mastering applications, precise stereo matching between channels, or matching volume when overdubbing on tracks you’ve previously recorded (provided you’ve written all down your settings). Infinite controls offer more precise setting capability. For example, if the gain you need is between two positions, are gong to tell a singer to back off the mic by a fixed amount or sing softer? Probably not. Your particular recording needs will determine which gain control method is better for you.
In order to manage your levels, preamps provide some form of visual feedback. These can be in the form of LEDs that show when a signal is near or about to clip, or VU (Volume Unit) meters, which are designed to respond to signals in much the same way our ears do. VU meters show average levels, and are not really useful for providing accurate information about transient and peak levels — that’s what the LEDs are for. True VU meters are more commonly found on the high-end preamps, while the less expensive units have VU-like meters that actually measure decibels. The volume unit corresponds to the decibel only when measuring a steady sine wave tone. As far as a make-or-break feature goes, true VU meters are not one of them. In reality, a simple LED overload indicator will suffice. Sometimes we can’t actually hear the overloads, which if otherwise not detected, will have a negative impact on your sound somewhere down the road.
M – S Decoding — What/— Do You Need It?
M - S is short for mid-side, which is a mic placement technique for stereo recording. The advantages of mid-side recording are mono compatibility, which actually provides a more cohesive stereo image, and greater control of the amount of stereo information (widening or narrowing the stereo field). And you don’t need a pair of matched stereo mics. Not many preamps feature this, and an M-S decoding (sum and difference) matrix is easily created in a DAW or mixer with phase reverse. If you work in multi-mono (overdubbing), obviously it’s not necessary, however, if you’d like to add “being there” feel and impact to your recordings, then you may consider a preamp with this feature. You’ll find M-S decoding on preamps such as the make standalone MS decoders.and . Some manufacturers such as
As Einstein once said, “A little knowledge is a dangerous thing. So is a lot.” Nowhere is this more true than in the world of specs (with the possible exception of building nuclear weapons). Specification listing is an area of consumer and professional electronics that can be the most misleading under the guise of providing objective measurements of performance. We don’t deny the importance of specs, but they must be handled with care. There are certain specs that if given in the proper context can be very helpful in choosing a preamp. In many cases, however, it is nearly impossible to use the specs to compare units, since the conditions used to obtain the data are often omitted. For example, if you see one preamp’s dynamic range listed at 118dB while another is listed as 122dB, it would be natural to assume that the bigger number is better. Not so. By itself, 122dB tells you nothing. Without reference to what bandwidth was measured or whether or not weighting filters were used, you simply have a number but no idea what the number is relative to. Hence, there’s no way to accurately compare. We’ve also seen a number of different ways that manufacturers express the same spec, which makes comparisons that much more difficult and confusing. Can we clear it all up for you? Not really, unless you’d like to take a four-year course in electronics, but if you’re interested in a greater understanding of how the specs are arrived at and what they may or may not be telling you, please see our sidebar “ .” There are certain specifications that are useful in preamp selection, which we discuss below. There are also specs that objectively measure of a preamp’s performance but offer no clue as to sound quality. These specs include THD, slew rate, frequency response, and phase response. Several units can have precisely the same numbers, yet sound completely different. To put it in musical terms, it’s like trying to learn harmony by analyzing Bach chorales on a blackboard. Without audio examples, the rules are meaningless. The same holds true for preamps. Unless you hear the unit you really can’t judge its performance. In that regard, your ear is the Supreme Court. (With Musician's Friend’s 45/45 Double Satisfaction Guarantee, you’ll have 45 days from purchase to audition the preamp before deciding that it’s right for you.)
Maximum Input Level (Input Headroom)
Basically, this tells you if the output voltage of your mic while capturing loud sound sources is going to overload your preamp. In order to calculate this, the specs you need to know are the mic’s sensitivity, which is usually (but not always) given in mV/Pa (millivolts per Pascal), and the preamp’s maximum input level or input headroom. The problem is to convert sensitivity into a maximum output voltage, which requires quite a bit of math, or a lookup table that plots sensitivity vs SPL with a resultant voltage expressed in dBu. From there, you can easily check the maximum input level of the preamp, which is also given in dBu. Keep in mind that sensitivity is a worst-case scenario. If a mic’s max SPL handling is 140dB (a jet engine at 10 feet) but you’re not going to record a source louder than 110dB (a chainsaw at three feet), then you can relax a bit. This is as close as we can give you to a rule of thumb: The sensitivity of most condenser mics hovers somewhere between 10 to 25mV/Pa, which at 130dB SPL (threshold of pain) will yield a maximum output voltage of anywhere from –2dBu to +6.5dBu. Most mic preamps should give you at least +10dBu of headroom. Your main use of a condenser mic will be vocals, acoustic instruments, and distance miking (drum overheads), which will certainly keep you well below 130dB SPL. For close-miking of loud sources such as kick drums, snares, and guitar and bass amps, you’ll mainly be using low-sensitivity dynamic mics. The only time you really need to concern yourself with this spec is if you plan on buying a specialty mic such as the DPA 4003, which has a sensitivity of 40mV/Pa, which is twice that of the average studio condenser. Even that mic can be used effectively with most preamps as long as you don’t put it up in front of a high SPL source. Again, you have to trust your ears. The best overall advice we can give you is to buy the best preamp you can afford.
In electronics, musical pitch is dealt with in terms of frequency, which is measured in Hertz (Hz). In essence, this is the range of your preamp’s “hearing.” Frequency range is commonly displayed as follows: 20Hz – 20kHz (k – x 1000, 20kHz = 20,000Hz). In reality, even though we can hear down to about 14Hz, not much happens in music below 40Hz save noise and rumble, and we can’t hear above 20kHz (with 17kHz being the most common upper limit for human hearing). So why is it that you see high-end preamps with frequency ranges as low as 4Hz and as high as 150kHz and beyond? While it is proven that there is acoustic content above 20kHz that is discernable, most mics and monitor speakers are limited to around 20kHz. The reason for designing beyond human hearing has to do with better phase alignment of frequencies in the audible range. (Please see sidebar: “So High it Hertz,” for an in-depth explanation by John La Grou, founder of Millennia Media). The same thinking also applies to the lower frequencies. In short, a wider bandwidth makes for a better sound.
EIN stands for Equivalent Input Noise. There are different types of noise that electronics are subject to, but the two that we are most concerned with are thermal noise, which all components produce, and noise from circuit resistance. Microphones have a source resistance (impedance) that generates noise. An amplifier also generates noise from its components and circuit resistances. When these two noises, the external and the internal noises are added together, we have an “Equivalent Input Noise”. However, this measurement by itself doesn’t really tell you exactly how good the preamp is. Basic rule of thumb: a tube preamp is going to have more thermal noise than solid state, however with any good design, the EIN value is going to be quite small. A preamp with a very low EIN value would be your choice for critical recording and mastering. A tad more noise is negligible and expected if you’re recording heavy rock and desire the coloration that comes with tube preamps.
CMRR (Common Mode Rejection Ratio)
In long cable runs, noise becomes an issue. Cables can pick up radio frequencies (RF) and other interference, which is why balanced cables are used for their noise-canceling ability. CMRR defines to what degree signals are canceled at the input of a balanced system. If you plan on using very long cable runs or are in an environment where electromagnetic interference (EMI) is an issue, make sure the preamp has a sufficiently high CMRR. The number is expressed in dB, but in order for this spec to make sense in terms of comparing it to other preamps, it must be stated at a given frequency. For example, 65dB by itself doesn’t tell you anything, however, >65dB @ 10Hz-22kHz tells you something about the preamp’s ability (pretty good in this case) to reject noise over a given frequency range. In most cases, you’ll see the spec given at one specific frequency (e.g. 40dB @ 1kHz), which gives you a basis for comparison. It is also assumed that this holds for all input levels.
This is one of the few specs that is fairly straightforward. Certain specialty mics have specific gain requirements. For example low-sensitivity ribbon mics require a great deal of gain in order to work their particular brand of magic. One problem with the way that this spec is shown has to do with whether or not the gain rating is based on balanced or unbalanced input and output, which can differ by 6dB (usually balanced or unbalanced input doesn’t affect gain), but it does affect output gain. If your heart is set on owning a ribbon mic, then you should be looking at preamps with a gain range of 60-70dB.
Preamp Buying for FTL (Faster Than Light) travelers
Just as certain songs can cross over into other genres, the sound qualities and uses of preamps can overlap. Below you’ll find some generalizations that will help you narrow your search.
By sound quality:
- I want a rich, creamy sound — Choose a tube preamp.
- I want a “colored” sound that will jump out of the speakers — Choose a solid state, transformer-coupled design.
- I want transparency and accuracy above all — Choose a solid state transformerless.
- I want good transient response and accuracy first, and be able to add warmth second — Choose a hybrid, modeling preamp.
- I want as much tonal variety as I can get — Choose modeling, hybrid, or any preamp with variable impedance or tone controls.
- I’m recording heavy rock and pop vocals. I want to add character or grit — Choose a tube or transformer-coupled solid state preamp.
- I’m recording electric guitars and bass — any preamp type will do. Read through numbers 1-5 above to decide where to look. A mono preamp will suffice; a Hi-Z instrument input would be a good feature to include. Instrument-specific preamps and DIs will also work.
- I need a preamp for recording drum overheads and percussion — Choose two-channel solid state: transformer design if you agree with #2 above, transformerless if #3, and hybrid if #4.
- I’m recording great vocalists, orchestral instruments, and live jazz. I want as true to life sound as possible — Choose a transformerless solid state, 2-channel, or multichannel preamp.
- I need a preamp to mic a drum kit —Choose a four- (kick, snare, overhead) or eight-channel solid state preamp with ADAT lightpipe or D-sub analog output (also, see letter C).
- I’m going to record my band live — Choose a multi-channel solid state preamp with chaining feature (cascadable).
- I’m just recording my voice and acoustic guitar live — Select a 2-channel preamp. Any of the above preamp types will w— your ear rules here.
- I’m recording electronic keyboards — keyboards can be recorded direct, however, if you want to add color, select a stereo tube or solid state/transformer design. Most keyboards have a mono output, but a 2-channel or stereo preamp lets you take advantage of the keyboard’s stereo presets.
Choosing your preamp
To help you choose, we’ve` divided color and transparent preamps/channel strips into examples from manufacturers who are most known for one type or the other. However, some manufacturers make preamps/channel strips that fall into both categories, which we also list below. Some makers specialize in tube or solid state designs, but we won’t make those distinctions here. That’s what our website detail pages are for. We’ve also included a section for budget preamps. To be honest, rather than color or transparency, affordability is what they are most known for. These manufacturers produce preamps of both varieties, and despite the low prices, can produce surprisingly good results. If you’ve gotten to this point (even on the fast track) you should know enough about preamp design to determine if a budget preamp will give you color or transparency. Happy hunting!
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Guitar & Bass Preamp
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