Glorified Gadgets or Essential Tools?
A preamplifier has a one job, just one little job to do, and that’s to take the tiny audio signal from a microphone or musical instrument and make it a bigger signal so that other recording hardware or software can work its magic. It’s a part of every audio signal chain, from studio recording to home stereos. Every strip on a mixing board usually starts with a preamp. Four-channel mixer? Four preamps. Seventy-two channels? Seventy-two preamps. So, if preamps surround us in endless quantities, why would we spend money to add another?
What Is Line Level?
You don’t need to be very deep into home recording before the concept of ‘line level’ emerges. Line level is one of the steps in the gain staging process.
Imagine you’re at an arena concert. Your favorite star is onstage singing. The path from the singer’s voice to your ears is a series of energy conversions and power boosts. Here is the step-by-step map of that path:
- The singer’s voice is converted to electrical energy by the microphone.
- The mixer boosts the mic signal to a standard level of electrical energy, upon which the next steps can work. This is called Line Level.
- Line level signal is fed through the channel strip, sent to effects units or monitors, adjusted with equalization and balanced with the rest of the band using the knobs and faders on the strip.
- Headphones require a boost from the line level signal. This is provided by the headphone volume control.
- The master output of the mixer feeds the beefy amplifiers that then power the huge speaker arrays. These amps, running thousands of watts, drive speakers that convert electrical signal back into sound, which travels through the air to your ears.
What Are The Types of Microphone Preamps?
There are two broad categories of preamps. A “personality” pre adds its own sound to your microphone signal. Before transistors and integrated circuits, vacuum tubes were the workhorses of the amplifier world. Hang out with enough guitarists and they will put you to sleep discussing the merits of tube amps. Tubes distort sound, that’s their nature, however they do it in a pleasing way. That’s the personality they add. Not all personality preamps are tubes, though. There are some great sounding solid state preamps that add their own sound as well.
The other preamp category is the transparent preamp. Just the volume, ma’am. These amps attempt to leave your mic signal alone, except to make it louder. Many preamps try this but fail. Others add character, but so gently you notice only how good they sound. There is no right or wrong here, only what you think sounds good. If you love the sound of your mic just as it is, you’d opt for a transparent preamp.
I Have a Mixer. Why Add a Microphone Preamp?
Amazing question! Glad you asked, since it’s the whole point of this article.
In the glory days of the professional recording studio, each facility had to be ready for whatever was thrown at it. James Taylor or Jimi Hendrix, the studio had the rooms, mics, signal processing and tracks to meet any need. So those huge mixing boards had expensive, heavy-duty electronics, including preamps, in every channel strip. Add-on preamps existed, but weren’t commonly used.
Flash forward to the digital age. The capabilities of computer-based recording opened up high-end recording to everyone. This takes recording out of expensive studios and puts it in the user’s home. Chances are you don’t need 72 channels, particularly if you’re recording your voice and maybe a guitar. Most of the time, you’re recording one or two tracks at once.
Your little six-track mixer may have four XLR mic inputs. Each of these inputs feeds a preamp, so you already have and use preamps. Also, you probably paid under $200 for your mixer.
Let me be clear here. There’s nothing wrong with the preamps in your $200 mixer. If you’re proud of the tracks you’ve made, continue to be. There’s too much swagger and machismo in the recording world. Don’t let anyone wave equipment around in your face. At the end of the day, it’s the result that matters. However, you can improve your chances of nailing professional results with the right preamp. I’m all about making life easier.
Some of today’s preamps attempt to duplicate the electronics and sounds of the classic mixing boards. The preamp package takes a portion of one strip and puts it into a box for the person who needs only a portion of one strip. A good preamp has the potential to give you audio performance offering pro results at a wee fraction of the cost of a classic mixing board.
After upgrading your microphone to a large diaphragm condenser, adding a preamp can be the best thing you can do to improve the quality of your sound, right up there with acoustic treatment and sound reduction in your recording room.
How to Use a Microphone Preamp
A preamp is the first step after the microphone, so if you’re adding an external pre (‘pre’ is hipster engineer slang for preamplifier), it will be what your microphone now plugs into. The preamp output will then connect to a line input on your mixer or audio interface.
XLR Connections: Those mic cable ends with either three pins or three holes are called XLR connectors. Pro mics use these pretty much exclusively. The preamp expects mic input using an XLR cable. These are common on most professional equipment.
It’s quite possible your pre has an XLR output as well. You could route this to an XLR input on your mixer or interface, but remember, there’s another preamp in there too, so this is not an ideal connection. It’s like driving around the block to cross the street.
If your pre only has XLR outputs, you will need an XLR-to-1/4-inch TRS adapter. A well-equipped music store will have these. The ideal output from your preamp connects to an input expecting a line level signal. Even the most affordable mixers and audio interfaces have line-in connections. Anytime you see that world “line,” you know your preamp out will connect.
Best Microphone Preamp For Your Budget
As with virtually all home recording gear, preamps come in all shapes, sizes, price ranges and levels of quality. The “get-what-you-pay-for” concept generally applies. Let’s look at three preamps from the bottom, middle and high end for home recording use.
Low End: Behringer MIC200 Tube Ultragain – In the $50 range, this unit runs your mic through a small vacuum tube to boost to line level and alter the sound of the audio. It’s a personality preamp that gives a quality of warmth, that tube distortion effect. With this model, you can expect some increased background noise.
This is an entry-level preamp, worth a try if you want to dip your toe lightly in the preamp pool. It’s useful for special effects and it can add crunch to electric guitars. The noise business probably prevents it from adding pro sound to your tracks.
Mid-Priced: ART Pro Channel II – This pre will put you back about $250. This is also a tube-based preamp, adding compressor and equalization functions to mix. It’s built into a rack-mount package, so you can set this up in a permanent studio installation, rather than a tabletop unit like the other two preamps we are looking at.
This is a fantastic preamp for the intermediate user who wants to add a complete channel strip. You can adjust the sound of your mic using the EQ settings as well as taming loud and soft sounds with its compressor.
High End: Focusrite ISA One – This preamp is faithfully designed based on the Neve recording desks of the 1980s that Sir George Martin, producer of the Beatles, commissioned for his world-class AIR Studios. This preamp sells in the $500 range street price. While technically it is a personality preamp, it is so subtle that many very sensitive ears will describe it as transparent. (Read my full review of the Focusrite ISA One Here)
This preamp concentrates on being a preamp, unlike the Pro Channel II, but it does what it does very, very well. Intermediate to advanced users after the very best quality sound.
You can spend much more on preamps, but since we are concerned with the home market we will stop here and look how each of these does its job. The same principles apply to the very high-end preamps.
Microphone Preamp Connections
|Behringer MIC200||ART Pro Channel II||Focusrite ISA One|
|XLR + ¼-inch TRS||XLR + ¼-inch unbalanced||XLR + ¼-inch unbalanced|
|Behringer MIC200||ART Pro Channel II||Focusrite ISA One|
|XLR + ¼-inch TRS||XLR + ¼-inch unbalanced||XLR Only|
Typical Microphone Preamp Features and What They Do
Gain sets the preamp for the strength of the incoming signal. Voice versus loud guitars, for example, create different signals for the preamp. Usually controlled with a knob, there are sometimes other adjustments available. The MIC200 has a button that reduces the signal by -20 dB. Press this in when recording loud guitar and have it out when recording vocals. The button sets the range of the preamp.
The ISA One has a similar button that selects range for its input gain knob, and has a second knob, called Trim, for further fine-tuning. As this unit has no output level control, careful setting of the input level is key to best results.
The Pro Channel II has a gain knob and a +20dB button for use with quiet sound sources. There is also a master output level control knob.
Every amplifier has a spot where it operates best. If you understand frequency/gain charts, it’s within the straight-line portion of the graph. If you’re not familiar with these, no worries. It’s a Goldilocks thing – not too quiet and not too loud.
Watch those meters. You don’t want signals to go into the red. In the old days, a little red was okay, but digital audio is less forgiving. Each of these preamps is analog. They can handle a hot signal, however the digital converters in your interface or computer may not. Get used to feeding a solid signal that doesn’t push the needle into the red or light up the red LEDs.
Phantom Power, Phase and High-Pass Filters
Each of our sample preamps has a button that provides 48 volts to power condenser mics. In fact, it would be difficult to find a preamp without this. Dynamic and ribbon mics don’t require phantom power (although there are exceptions). Dynamic mics are impervious to it and the presence of power has no effect.
Ribbon mics are another matter. Fragile by nature, plugging a ribbon mic into a circuit with phantom power can kill it. Yes, there are exceptions and modern ribbons are better protected that vintage cousins. These beasts are rare and not common outside pro studios.
A phase switch is another common preamp control, and all three of our examples have one. To convert acoustic sound into electrical signals, the diaphragm of a mic moves in and out, absorbing sound pressure waves. It’s a vibration, back and forth, or up and down when plotted on a graph.
Electronically, that can be reversed so that the resulting electrical wave goes down first, instead of up. When you are using more than one microphone and they are close to the sound source, their combined signals may interfere and cancel each other. Press the phase button on one pre and the problem is solved.
High-pass filters have a variety of names and types. The MIC200 doesn’t have one. The Pro Channel II has a Lo-Cut knob that selects the cutoff frequency. The ISA One has a button called HPF for, strangely enough, High-Pass Filter. This control removes low-frequency content, usually around 80 hertz. For vocals in particular, there is rarely any desirable sound below this level. It’s all just plosives (P-pops) and rumble transmitted through a mic stand, so press that button, and those sounds will be reduced if they don’t altogether disappear.
Explaining impedance is boring and filled with math and not easy to understand. It is critically important to how mics and preamps work together, but you can reap the benefits without understanding what’s happening. If you want to geek out, click here for the whole story.
If you’re using an entry-level preamp such as the MIC 200, no worries, the impedance can’t be adjusted. This isn’t a drawback. Mixers at all price points rarely have any impedance switching at the preamp stage.
The other two both have selectable impedance. The Pro Channel II uses a dial to adjust between 150 and 3,000 ohms, while the ISA One has four settings, selected by a push button.
Every microphone has its own impedance and matching that to the preamp input gives the best performance. If you’re playing test equipment, this is probably true. However, when you listen to the various combinations, it comes down to how it sounds. Nothing will blow up if you select the “wrong” impedance, so it becomes another tool in the pursuit of tone.
The difference between project studio results and pro studios is one of very small increments. Achieving these advances can be difficult, particularly when you’re competing with very expensive equipment.
Adding a preamp permits you to affordably introduce high-end electronics into your recording setup. This is an augmenting purchase. Your mixer or interface likely has a perfectly usable preamp that you’re already using.
The low-cost preamps are often special effects pieces, such as the MIC 200, which simply introduces a tube circuit and more gain.
Mid-level equipment such as the Pro Channel II replicate more expensive electronics, compressors and EQ that may expand the versatility of your mic collection and help you craft more distinctive recordings.
The ISA One and other high-end preamps bring a touch of the pro studio to your project studio. Even your cheapest mic may find new life.
The preamp concept is not rocket science. It has to happen to provide line level. Now you’ve got a foundation in the what, why and how of preamp use.
Questions? Comments? Don’t be shy, post below. Sign up for more spam-free home recording information directly to your mailbox.