Preamp Topics:
» Which should I buy, a Preamp or a Channel Strip?
» Tubes vs. Solid State preamps.
» The hidden secrets of matching mic and preamp impedance.
» How can multiple preamps help me and my studio?
» Why are some preamps more expensive than others?
» What to Look For... Studio Preamps

Which should I buy, a Preamp or a Channel Strip?

Actually, it's not so much a question of which to use as much as when to use one or the other. Depending on what you plan to do, the advantages of one can be the disadvantage of the other, yet that same disadvantage in other circumstances can be an advantage. Confused yet?

A channel strip is comprised of a number of signal processing tools including a preamp, usually followed by a compressor, an EQ section, and in some cases a de-esser or an enhancer (or exciter). If you are recording vocals, for example, this gives you every processing tool you need for professional vocal recording in one convenient and cost effective unit. Since the electronics are all taking place inside the same box, the chances for noise are diminished as opposed to going from separate preamp to compressor to EQ, and etc. By the same token, each circuit in the path from mike to recorder does add some noise and signal degradation. In order to get the cleanest possible signal, a single preamp with no other electronics in the circuit is the best option. This gives you the ability to add in other processing as you see fit. Now we begin to see how advantage and disadvantage can flip-flop.

So why choose one way to go or the other? It all depends on your purposes and the sound you're going for. In the beginning, we mainly had preamps to get signal into recording devices, followed by EQs, compressors, and other processing devices born of need and experience. Eventually, these separate devices were built into consoles for convenience. Each separate channel on a console had a preamp, an EQ section, and eventually we added compression and gates. Certain consoles became known and prized for their particular sound, such as Neve, API, Trident, Focusrite, and others. Unfortunately, they cost a large fortune and were out of the reach of most people until someone got the idea to take one channel of a legendary console and put it in a box. This is the advantage of the channel strip. For a reasonable amount of money, you can have one world-class recording channel for your DAW (which you can use again and again). So, for say, $2000-3000, you can have the sound of a million-dollar console.

This raises the question, "Why doesn't everybody use channel strips?" the answer is because there are certain units made by different manufacturers that have their own particular sound. Plus, the interaction of two different units can create a unique sound altogether. For example, many engineers like the sound of Neve preamps, and EQ, but prefer the sound of Universal Audio compressors. The ability to mix and match components is similar to an artist having more colors at their disposal. Ultimately, it comes down to personal taste, experience, and of course, budget.

Tubes vs. Solid State preamps.

Do tube preamps really sound better than solid-state preamps? As with many, discussions in which technology, artistry and aural perception are combined, this issue has no clear answer. But we can look at some basic details objectively, and hopefully help you make a more informed buying decision.

Sol•id State adj.
	Electronic components and circuits where signals pass through solid semiconductor material such as transistors and diodes as opposed to vacuum tubes where signals pass through a vacuum, or relays, which are electromechanical devices. "Solid State" was a big buzzword in the early 1970's because solid state equipment was not only less expensive, but often thought to be more reliable in the field than the tube based predecessors.
Vac•uum Tube n. Abbr. VT
	An electron tube where virtually all the air has been removed (creating a vacuum), thus permitting electrons to move freely, with low interaction with any remaining air molecules. Early tubes had two electrodes (cathode and anode, or plate) and were known as diodes. Later (1907) a grid (or control grid) was added, creating what is known as a triode. The grid provided real-time control of output levels, where a small voltage applied could regulate the current passing from the cathode to the plate, creating the first practical amplifier.
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First of all, understand that everything in the signal path can have a noticeable effect on the sound of your track - the microphone, the cable, the power supply (for condenser mics), the room noise, the impedance of the preamp, even the humidity! So before you make a long-term decision on a preamp, be sure to look into all the elements of your signal path.

Tube circuits are sometimes elevated to mythological status, primarily because they were all we had for about 50 years before solid state came along. But in real world terms a good solid-state preamp can sound much better than a poorly designed tube preamp. Conversely, a good tube preamp usually sounds better than a poorly designed solid-state preamp. That's a pretty simple quality issue.

It's safe to say that both tube and solid-state preamps - when properly designed - exhibit low distortion throughout their normal amplitude range. The difference in sound becomes evident when the circuits run out of headroom. Solid-state devices tend to abruptly transition from low distortion to extreme distortion (clipping). This is actually a good thing because, when operated right up to their maximum level (generally a higher level than a tube circuit), solid-state preamps can maintain excellent performance.

It's the nature of the distortion that makes the two types sound different. Solid-state circuits run out of headroom when the output voltage exceeds the power supply voltage. The result is gross distortion - the output becomes a square wave. Square waves are not sounds that we normally usually consider musical, so our subjective response to them is negative.

When a tube circuit distorts, the primary distortion product is even order harmonics, with the second harmonic dominant. It so happens that musical instruments also produce primarily even harmonics. By definition, that's what makes them "musical." So you could say that tube circuits can add a musical component to recorded sound. Fortunately, you can take your choice - keep the level reasonable and obtain good clean audio, or run the circuit into distortion and generate some harmonics that weren't there to begin with.

In circumstances when the preamps aren't being driven into distortion, it's reasonable to say that tube circuits always generate a certain degree of harmonic distortion, simply as a result of the way they work. Some tubes, specifically triodes, also exhibit a form of low pass filtering attributed to the Miller Effect - the charging and discharging of the plate-to-grid capacitance as the input signal changes. These factors are a large part of what is often described as tube warmth, and we - meaning most musicians, recording engineers and the listening public - have basically agreed that this is a pleasant sound. Solid-state circuits, with relatively low distortion and no inherent low pass filtering, might actually provide a more accurate capture of the sound, but this is often perceived as "thin" or "sterile" in contrast to tubes.

So we're really saying that we like tube distortion to a certain degree, even in vocals and other critical recording situations. And many solid-state preamps actually incorporate circuitry that attempts to recreate tube-style distortion. And the message for you, the recordist in search of a preamp, is to use your ears and choose what sounds best to you.

The hidden secrets to matching mic and preamp impedance.

Matching impedance as far as microphones and preamplifiers goes, is a widely misunderstood term. Most microphones can be used very satisfactorily with most preamplifiers and as we'll see later, true "matching" is may or may not be desirable. However if you are seeking a particular quality, tone, coloration, character, then picking the right combination of equipment can be very helpful.

What is (Ω) Impedance?
Every microphone inevitably has output impedance, and every microphone preamplifier has input impedance. These characteristics simply describe the "resistance" to signal current flow out of the microphone circuitry and into the preamplifier. The symbol for impedance is "Z," hence the term "Hi-Z" as applied to inputs and outputs. (Guitarists should be familiar with Hi-Z.)

In practice, the input impedance of a microphone preamplifier can have a great effect on the sound of the recorded signal. It is mostly the interaction between the output impedance of the mic and the input impedance of the mic preamp that causes audible differences as the result of an "EQ" effect. Also, the (often quite complex) impedance of a mic pre will interact in a unique way with the output impedance of an individual design of microphone. This is why certain engineers will have a mic and preamp of choice for different usages.

It helps to think of impedance in terms of having a nozzle at the end of a garden hose. The garden hose (mic) is a low impedance source (there is little resistance to the flow of water) and the nozzle (preamp) is the higher impedance of the input being fed by the hose. When the nozzle valve is closed (open circuit): Input impedance is very high, pressure (voltage) is at maximum, and flow (current) is zero. Now open the nozzle just a little: Input impedance reduces but remains high, pressure reduces but remains high, flow is small; you can hear lots of hiss from the spray (high frequencies). As you continue to open up the nozzle: input impedance reduces further, pressure reduces, flow increases; hiss from spray becomes less noticeable. With the nozzle open all the way: input impedance is very low, pressure falls dramatically, flow is greatest; hiss from spray all but disappears. As you can see from this example, as the preamp's (nozzle) impedance is lowered, the high frequency content is lowered as well.

Variable Impedance Preamps:

The Focusrite ISA 428 Pre Pack is a 4-channel variable impedance preamp.

The Summit Audio 2 BA-221 is a 1-channel variable impedance preamp.

Matching microphone and preamp impedances to the same value (power-matching) is not necessarily desirable since it reduces both the level and the signal to noise ratio by 6dB. For dynamic and condenser microphones, the preferred preamp input impedance is generally about ten times that of the microphone output.

Some preamps offer variable input impedance, which allows the level of transformer and microphone interaction to be adjusted. It is therefore possible to create a variety of mic/mic pre colors due to the EQ-like effect. The advantage of this is the ability to shape frequency content while recording without adding an EQ device in the signal path, with the inherent noise and signal degradation that follows with more components in the signal path. Keep in mind that settings are a matter of taste. You won't destroy your mic or preamp through experimentation, but you may very well find exactly the sound you're looking for.

How can multiple preamps help me and my studio?

Originally, the mic and instrument preamps used in recording were built into the mix console; it was basically an "all in one" environment in which recording engineers placed their trust in the console builders. From the beginnings of electrical recording in the 1920s up to the 1970s, most major studio consoles were custom designed, hand-built units whose creators were equally experienced in all angles of mix technology: preamps, compression, equalization, signal routing, etc.

Beginning in the 1960s a new breed of designers (two notable ones were Joe Meek and the living legend Rupert Neve) began to focus on the individual components of the mix chain and a new species of "boutique" outboard devices began to appear: individual preamps, compressors and equalizers that could be plugged in to an existing console. Recording engineers began to perceive differences in the sonic qualities of individual components.

Today, if you look at any commercial studio's equipment list, you're likely to find a variety of outboard preamps from different manufacturers included in addition to the ones built into the board. And if you are just getting into recording, whether in your home studio or at a commercial facility, your question might be, "Why have so many different preamps that all seem to do the same thing?"

Let's break this down to a couple of basic concepts. First, if we leave all budget considerations aside, a preamp can be two things:

1. A utility device that's necessary to bring mic and instrument signals into your mixer. The first thing most students in recording classes learn is that their prime directive is to capture the sound of a performance as accurately as possible. But even with this clear definition of function, many variables come into play. "Capturing" the sound of a classical string quartet in a medium-sized concert hall requires a different approach than does "capturing" the breathy alto voice of a female jazz vocalist, or the slamming impact of a Led Zeppelin-style drum kit. And different preamps are more effective at one or another of these tasks just by design. More on individual applications in a minute.

2. 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.
   
   

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:

1. 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.

2. 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 lowpass filtering caused again by the tubes' performance).
   
   
   • 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.
   
   
   • 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. Here's where a variable-impedance preamp can be an outstanding addition to your studio.
   
   
   • 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. For more mic-intensive situations a 4- or 8-channel unit provides the multi-channel performance you need.

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.

Why are some preamps more expensive than others?

The reasons why one preamp would be more expensive than another are pretty much the same reasons one automobile is more costly than another; better parts, careful construction, and sometimes, its desirability born of myth and legend. The question is, is more expensive always better? Let's talk about what goes into making a high-end preamp.

To build a sonically superior product, it requires expensive parts and labor-intensive wiring techniques. Some preamp makers concluded that the best performance could be obtained with a design utilizing transformers, although the cost of superior transformers is very high. Some manufacturers even have transformers custom made for them. Transformers are also used in the power supply. Correct power supply and signal grounding is a prerequisite to high-fidelity audio performance.

Wiring is also a reason for expense. Certain materials are better conductors of electricity, the best conductor being gold. High-end preamps will use gold-plated connectors and sealed, gold-contact precision relays for switching in the audio path. Also, the wiring itself will be point-to-point, meaning that no printed circuit boards are used. Keep in mind, that in terms of design philosophy, the best preamp is a straight wire with gain. Point-to-point wiring means a shorter more direct signal path. This requires hand wiring which is naturally going to be more expensive in labor costs.

The quality of components such as tubes, transistors, resistors, capacitors, inductors, connectors, and even solder, have significant effects on sonic quality.

People who design preamps seem to take all this stuff seriously. In the end, you usually get what you pay for. That doesn't mean that we believe less expensive preamps don't have their purposes. Not only will they add a different color to your arsenal, many of them sound truly great! You really need to rely on your ears, and the ears of other trained professionals. Learn what you can, and listen to as many models as possible.