One Size Doesn’t Fit All, Part Two: Microphones and Mic Preamps

One Size Doesn’t Fit All, Part Two: Microphones and Mic Preamps

Written by Paul McGowan

After our brief examination in Issue 205 of the recording chain front end – the microphone – it's good not to forget what follows the microphone. In the same way a phono cartridge requires a phono preamplifier to process and amplify the signal – and we all know how important to sound quality the phono preamplifier is in the chain – so too do microphones.

Both microphones and phono cartridges are mechanical transducers that convert motion into electrical energy. In the case of a microphone, it is converting changes in air pressure, while with phono cartridges it is the motion of the needle tracing the plastic grooves in the vinyl.

Both transducers have very low output and must be amplified before you can play them back on a reproduction system or feed them into an A/D converter to record them.

And, just like with moving-coil and moving-magnet cartridges, different microphone types have varying output levels that require either more or less amplification.

If we break down the main microphone types into three categories they would be: condenser, ribbon, and dynamic.

By far, the most common and preferred microphone type used in the recording studio today is the condenser microphone (like the Neumann, Telefunken, and Gefell models I’ve mentioned). Condenser microphones operate using an electrically-charged diaphragm placed close to a backplate. When sound waves hit the diaphragm, the distance between the diaphragm and backplate changes, causing capacitance variations that generate an electrical signal. It’s somewhat the opposite of the way an electrostatic loudspeaker works.



The stuff of legend: A Neumann U 67 vacuum-tube condenser microphone.


Ribbon microphones are today mostly relics used for specific duties in recording studios. They utilize a thin strip of metal (usually aluminum) suspended between two magnets. When sound waves hit the ribbon, it vibrates, inducing a small electrical current proportional to the sound waves. These mics are amazing on horns and blaring instruments.

Dynamic microphones are everywhere. They are versatile, handle huge dynamics, are low in cost, and are most widely used in live performances as well as specialized applications in the studio (like high-dynamics applications such as recording drums). If you ever attended a school function in the auditorium it's likely you were listening to some administrator drone on through one of these. They operate using a diaphragm attached to a coil of wire suspended within a magnetic field. When sound waves hit the diaphragm, it vibrates, causing the coil to move within the magnetic field and generate an electrical signal.

All three types of microphones, like phono cartridges, must be amplified by a preamplifier before we can use them to record or listen through a PA system.

In the case of the condenser types, they need two stages of preamplification. In the same way a moving coil cartridge requires the additional gain boost of a head amp, condensers do as well. This "head amp" is built into the condenser microphone and receives power through its connecting cable. In most condensers the external power needed to run their internal head amp comes from what is known in the industry as "phantom power." In pro applications this is 48 volts DC. In consumer versions that connect via USB, it is +5V and inside the microphone is included an A/D converter and amplifier. In the case of the Neumann U 67 and the Telefunken stereo mic, the vacuum-tube head amp in the microphone body receives its power from an external box where the higher voltage power supply is located.


Microphone Preamplifiers

How many of us would argue that the quality of a phono preamplifier doesn't matter? That we would hear little difference between an Amazon special and a Stellar Phono Preamplifier?

Hard to imagine, especially on a high-resolution audio system. Phono preamplifiers are essential components to get your turntable/cartridge setup to sing.

The same is true for microphones. In many of today's proliferating explosion of home studios, USB-powered microphones and cheap knockoffs of microphone classics abound (as do the growing number of substandard recordings). And to think they don't sound different or their differences can be EQ'd out?

Not happening.

But then why would we be surprised? 99.9 percent of all consumer electronics, like 99.9 percent of all do-it-yourself studio setups, have average sound quality. In fact, they define average. Which is what they are supposed to do, and they do it well.

But we're audiophiles and by definition, we are anything but mainstream average. We invest in better, above average, systems. The same can be said for the rare handful of (dwindling) high-end recording studios and beautifully-recorded media.

It's one of the reasons we started and continue to support Octave Records. We, along with the handful of others like Blue Coast Records, Native DSD, Chesky Records/HDtracks, and Reference Recordings, pay attention to every aspect in the recording chain – just like we audiophiles pay attention to every aspect in the playback chain.

All microphones must run through a preamplifier to have enough output signal level to feed the A/D converter. Just as in high-end audio reproduction, the design and quality of that preamplifier has HUGE impacts on sound quality.

At Octave Records, we have invested in multiple types of preamplifiers, including both solid-state and vacuum-tube (and a long-term project of building our own based on Darren Myers’ and Bob Stadtherr's design ideas).

Having worked with all these preamplifiers over the years I have settled on one type of preamplifier that for me makes magic. Vacuum tubes. In particular, the Manley vacuum-tube preamplifiers from our good friend EveAnna Manley.



May the Force be with you: the Manley Laboratories Force four-channel mic preamp.


While vacuum tubes are fun and interesting in the playback chain (like in our BHK Series or Stellar M1200 amplifiers), they can have far more impact on recording than they do in playback. Why? Because in playback we have more "control" in the expected dynamics. Once you buy an SACD or download from us, it has been mastered to ensure dynamic levels never exceed 0 dBFS. The same is not true with microphones.

And there is more.

In the playback chain our goal is to accurately reproduce what is on offer from the recording. Here, we don't want to color or in any way change what is being given to us. When we design our equipment, we don't choose vacuum tubes because of their colorations. We choose them because in that circuit, they make audio magic – magic that can be designed using multiple technologies. The same is not always true in a recording.

That is because the goals of a recording differ from those of playback.

A recording is more like a work of art. You're painting a picture and you want to capture as best you can the rich musical notes and voices. You're actually shaping them to make magic.

I am reminded of a recent recording session for an upcoming Octave release of wonderful cover songs. One of our excellent artists, Alicia Jo Straka, is a beautiful singer and she was working on her version of a few classic Ella Fitzgerald tracks. Alicia's gorgeous voice was captured on the Neumann U 67 and amplified through our wonderful Manley vacuum-tube preamplifiers. A fully vacuum tube chain of rich sound. Only, Alicia's voice didn’t have that lovely intimate quality the track cried out for.



Alicia Jo Straka in the recording studio.


What to do?

Work the microphone. You see, in the same way we might adjust VTA on a cartridge, or reposition our speakers to accommodate the room, the distance a performer is from the microphone has a huge impact on how it sounds (the same is true for loudspeakers). Closer to the microphone and we get what's known as the proximity effect, where the sound is richer with more midbass. Intimate. Sensual. So, on the soft notes, Alicia moved in close and "made love" to the microphone. When she got louder, she moved away (you've no doubt seen singers doing this on stage).

In the end, as we shape the sound, it is the combination of the recording chain electronics and technique that creates the recordings that we love.

The preamplifier is a key in that chain.


Essential Differences

We’ve waxed on about microphone preamplifiers and how important they are to the recording chain.

A couple of folks have asked me what brands of mic preamps we have in house that are solid-state, and they are made by Grace Design, and Forssell Technologies. Both are excellent preamplifiers that sound wonderful, though as mentioned, my go-to preamplifiers are the vacuum-tube Manleys.



A Grace Design M201mk2 mic preamp.


How do microphone preamplifiers different from, say, a BHK Signature home audio system preamplifier?

Let's have a look.

An audio preamplifier like the BHK has the following at its core:

  • Multiple inputs
  • High-impedance direct-coupled inputs (47kΩ typical)
  • Gain of no more than 20 dB
  • Volume, balance, and input select and a remote control
  • Low output impedance 

A microphone preamplifier has at its core the following:

  • One balanced dedicated input
  • Low-impedance transformer-coupled inputs (1kΩ typical)
  • Gain of typically 50 dB to 60 dB
  • VU metering
  • A volume control for the input
  • A 48-volt phantom DC power supply to feed the internal microphone preamplifiers
  • Low output impedance

So, basically microphone preamplifiers are low impedance in and out with high gain, low noise, and loads of headroom.

Audio preamplifiers are high input impedance, low gain, low noise, low output impedance.

They’re the "same" in that they amplify a small signal into a big signal and provide a means of changing level. In all other respects they are very different beasts.




A preamplifier intended for home use, like this PS Audio BHK Signature Preamplifier, differs in functionality, performance and even appearance from a preamp designed for pro applications.


Out of Sight, Out of Mind

As we wrap up our little miniseries on microphones, it occurs to me how little attention we pay to them. Which, if you think about it, is weird.

With the exception of synthesizers, drum machines, and perhaps a few electric guitars and electric pianos, 99 percent of everything ever recorded has passed through a microphone and its preamplifying chain. And the sonic characteristics of microphones are as extreme and all over the map as they are with phono cartridges.

To be clear, this isn't like the differences we audiophiles argue over between cables and power conditioners. No, the gaps in performance in microphones are as enormous as the ones we think of in the vinyl chain – a Shure V15 versus a Koetsu moving-coil cartridge, for example. 

One of the microphones I did not write much about is the rare (today) ribbon type. These ribbon microphones were once the mainstay of recordings, but today, they are generally used only on specific recording techniques, like capturing the blare of a trumpet without a resulting sound that make you grit your teeth.

Renowned for their smooth and natural sound reproduction, ribbon microphones often feature a bidirectional (figure-eight) polar pattern, enabling them to pick up sound from both the front and back while rejecting sound from the sides. Despite being passive devices that do not require external power, ribbon microphones are fragile and susceptible to damage from excessive wind or loud sound sources.

On the two most recent Octave Records releases by trumpeter Gabriel Mervine, I beautifully captured the sound of Gabe's horn with a classic ribbon mic weighing over 10 pounds (because of its enormous magnets). Just recently, I tried to use that same microphone to capture the honk of a baritone sax, and it sucked. Blurred, too rolled off. I moved over to the Gefells I talked about previously, and…magic.

The point is, all of our recordings are the result of sounds and signals passing through sonic transducers that are all over the map. Which reminds me also of the opposite end of the audio spectrum: loudspeakers.

Loudspeakers stare at us, so we pay attention. Microphones and their associated amplification chains are out of our control, out of our reach, and out of our thoughts.

Yet nothing else in the entire chain plays such a pivotal role.

Out of sight, out of mind, yet not out of our musical experience.

One Last Thought…

Of course, that's probably never the case as each thought leads to the next, but it makes for a good subhead.

In any case, it occurs to me that as we strive so hard to get as close to accuracy as possible in our high-end systems, we're trying to do two things: uncover all that is on the recording, and do so without affectation. In other words, create a perfect reproduction of the live event, where instruments and voices sound like themselves.

Pulling back for a moment to look at the big picture, we see that the real meaning of "live event," in the recording studio or on stage, has actually more to do with getting right with what the recording engineer captured, as opposed to what we believe to be the correct sound of instruments and voices.

Why does this matter? Because using our tweaks and expertise to get a clarinet to sound like a clarinet may have a bit of futility built into it. How accurate was the recording? If I, as the engineer, capture more of the upper squawks of the reed as opposed to the body of the instrument and you, as the listener, try and make adjustments to your system to compensate, we're trapped in an endless loop doomed to failure.

What do we do? My first impulse is to figure out a way to make a perfect recording that captures the sound of specific instruments, that we might all choose to rely upon as the standard. My second thought is how flawed that idea is.

Or is it?

I have told this story before, but just recently, while recording Octave's Steinway piano and a soprano saxophone, I was surprised by the comment both musicians made to me upon coming into the control room after their session. Listening to the playback on the aspen FR20 loudspeakers, they both remarked how "it sounds better in here than it did in there."

"Better than live?" We've been down this road too.

Just some final rambling to ponder.


This article is based on a series of Paul’s Posts from March 2024.

Header image courtesy of Shkraba.

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