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Here's a comment received from Mike H (that's all the identification I have)...

David, Just read your new article on mic preamps [I don't know which one, but here's an interesting one from the distant past - DM]. I do not contest your opinion, but I would like to tell you what happened to me:

First, FYI, I do voice over and use a Lawson L47 MP II tube mic. A long time ago I got a Great River mono pre for about $1100. Got a good sound, liked it. Then I read that -- and I think it was at Audio Masterclass -- that most console pre's were about as good as outboards. So I A/B'd this pre against those in my Tascam 1516, hardly a top-end desk.

I found the only difference was that if I boosted 100 Hz on the console, the console's pre made that frequency muddy and the Great River did not. Since I either never touch 100 Hz or if anything attenuate it, I immediately sold the Great River. Some time later I read about A-Designs and that they made a pre called a P1 (500 series), based on their Pacifica pre, which in turn is modeled after the pre's in the Quad 8 console; it was getting good press.

I got one, and it made a significant, and instant, improvement. In fact, I went a couple of months listening only to tracks made using it. Then one day I punched up a track made before I had the P1, and David, a pretty bad midrange hump jumped out at me, bad enough to make me think, "What did I see in this microphone before I had this preamp?!"

I went back and forth between tracks made with and without this preamp. The P1 makes the Lawson easily sound three times better than without it. I have 30 years' experience and it took me at least 20 of those years before I really started listening critically to things. Cheers, Mike H.

There's only one point here that I would disagree with, and that's about whether I said that console pres were as good as outboard. My position is that if someone can't make a recording of professional quality using the preamps in a decent-quality console, Mackie/Soundcraft or better, then the problem isn't with the equipment. And also if anyone's biggest problem is their preamp, then wow they must really be coasting through life in all other respects! But in all areas of audio one can always aspire to better and there are always new textures to be explored. So in that sense, outboard preamps are very welcome.

Tube character

Back to Mike's point, so how can mics and preamps interact with each other? Well there are two ways that are easily explained. The first is that tube mics have character. By 'character', I mean imperfections in their distortion, frequency response and noise performance, compared to a microphone that is designed to be accurate. It is impossible to look at an individual character mic's performance figures and know how it's going to sound. You have to listen to it, and listen to it on a variety of sound sources in a variety of acoustic environments. And even then, there is something about the 'mixability' of a sound texture that you can't tell just from a single voice or instrument outside of its proper context.

Tube preamps can have character too. So when you stack preamp character on top of mic character, the range of possible textures is huge. The same applies where transistor mics or preamps have designed-in character or defects in design, although the transistor sound has never been as popular as vacuum tubes.

Impedance mismatch

This is tricky to explain without going through many paragraphs of electrical theory, with diagrams and experiments you can try at home. It is all easily understandable, but the explanation is long-winded.

So what I'll say is that a microphone might have a flat frequency response with no load, i.e. it is not connected to anything. But as soon as you plug it into a preamp then the preamp loads the mic and the frequency response changes. Different preamps present a different load to the microphone and thus the frequency response changes in different ways.

The mic manufacturer might do an 'aha' and design the mic to have a flat response into the kind of load a typical preamp might present, which is of course what they do. But then someone might use a preamp that loads the mic differently. The frequency response you would get from any particular combination of microphone and preamplifier is hard to predict and the only real test will be to listen, and also judge the results in real-life projects.

So many possibilities, so little time...

If you have a particular combination of microphone and preamplifier that you love, and gets great results that please your clients, then clearly you are onto a good thing and should probably keep it a secret from your competitors.

If you're after an accurate sound, then you'll be considering a small-diaphragm capacitor microphone and a transistor preamp (which may be onboard in a console). You'll compare what you hear through the mic and preamp with what you hear acoustically direct from the sound source to your ears.

If you're after a 'character' sound texture, then the question of what kind of texture becomes very significant. It wouldn't be practical to test every possible mic/preamp combination. Probably the most practical course of action is to find a mic that you really like, then search out a preamp that makes it sound better, or more the way you like it.

Anyone with an interest in audio is bound to want to explore the vast range of possibilities that different mics, preamps and mic/preamp combinations can offer. It's just a question of how much time, money, energy and personal commitment you want to invest. There really does come a point where you have to consider that other aspects of your work are important too!

By David Mellor Saturday May 18, 2013
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