Part 9 – Microphone Inline Preamps

If your soundcards preamps are noisy or low-volume you may need to add an external inline preamp to get true line level voltages. In such case you will no longer use the “mic-in” jack, but rather the “line-in” jack (see Part 8).

Inline preamps come in a variety of sizes with differing features. Below are some key features you would find.

1.      Variable input and output gain controls

2.      +10 up thru +20 dB gain up switch

3.      +48v phantom power

4.      VU meter (either analog or digital)

5.      both XLR and ¼” balanced phono jacks.

6.      Polarity / Phase Reverse Switch

 To help choose what you should look at getting you again to need to know some basic terms and concepts.

The first would be to understand preamps can and will color your sound. Meaning if you have a nice warm sounding microphone and put it thru a preamp which has circuitry that produces a bright, thin sound you will not get good results. Same if you put the warm sounding microphone thru a very warm sounding preamp you will get a big boomy, possibly muddy sound. This is where the term “transparency” comes in. Transparency refers to the sound coloration of the preamps meaning simply does the preamp change the sound that is coming into it. You might accept this fact now, no preamp on the consumer market for less than a few thousand dollars will be truly transparent. But having said that some are closer than others.

In choosing a preamp you need to keep in mind your vocal characteristics or whatever you will mic i.e. an acoustic guitar or a Marshall half-stack. Also keep in mind the microphones you are using, are you using dynamic microphone? Is it neutral sounding like a Shure SM-57 or is it fat and warm sounding like the EV N-dyn 767a. Are you using condenser microphones? Large diaphram or small? Is it a thin sounding mic or fat? Will you need phantom power, etc? We will get into microphones in another section. Your local pro-audio expert should be able to help you with your choice if you know what you are after.

There are 2 types of mic pre-amps you will encounter in your search, tube and solid state. The differences here are major and worth noting. In by common conception and old technology digital recording is considered to be 2 dimensional, flat, sounding digital. That is because analog signals contain what is known as harmonic distortions that seem to add life to a recording. Our ears are analog and when we hear sounds they are filled with harmonics giving us 3 dimensional hearing. So the digital recording world has had to overcome for the lack of harmonic distortions in digital audio. This is why a Vinyl album will sound better than a CD of the same music. Though today’s music buyers are not familiar enough with the analog sounds of vinyl to appreciate depth and sound placement, many home recording enthusiasts are and there is the where the debate as to which is a better medium to record in, analog or digital.

Now a tube mic pre is designed to add harmonic distortion to “fatten” the sound by way of a tube altering the analog or digital signal. This is both good and bad. It is good because they will add grit to your vocal that will make it sound fuller and more natural. It is bad because it colors your vocal and what you get in your recording is what you get, you can’t remove the colorations without affecting the vocal itself. The tube pre is a great way to go if you are using a very brittle (thin and bright) sounding microphone.

The solid-state preamp is opposite the tube in characteristics. It’s purpose is to be transparent and not color the sound. This will allow you to process the vocal afterwards with plug-ins to add whatever you want retaining the original signal. You can add harmonic distortions after the fact with a tube compressor plug-in, but in the consumer realm this can lead to “processed” sound if the plug-in is not very good, you can also use inline outboard effects such as a tube compressor.

The waters are now muddied, which then is better? Neither and both, there is another technology that comes into play here and that is the analog-to-digital converters on your soundcard. We are not going to discuss this technology so we will go directly to where the rubber meets the road… how does it sound with your voice, your mic and thru your soundcard. What you are going to find in the consumer realm is all going to be subjective to your tastes.

Another source of preamps is a mixer. Of you have a mixer laying around you can use the mic and trim/gain settings there and use the mixers line out or preamp out.

Personally I use solid-state preamps that are found on my Aardvark Q10, they are fairly transparent giving me a lot of flexibility with different mics. I use a tube compressor on the mic channel insert to add harmonic distortions and I can season it to taste. Like anything else you can overdo it. When we discuss signal chain we will cover this a bit more in depth.

Here is a link to a Musicians Friend do a search on microphone preamps.

Basic Home Recording ©2003 by Jim Goodman. All rights reserved. You may download and reproduce entire document only for non-commercial purposes providing this copyright exists on all copies. All other uses require a written request to jgoodman@alltel.net or thru http://psalm149.com

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