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Microphone Preamps

What are microphone preamps and how did the legendary recording studio engineers of the past use them?



At The Recording Session Vault, it is an important component of our mission to promote an understanding through education about how the great music of the past was created. While part of my mission is to write biographies of the people behind the music, feature articles about the great studios, and to examine the technologies and to spotlight the companies that created them that have been so crucial to the development of popular music, it is also important to understand how the process of creating music actually worked, as well. With this educational series, we will explore the following topics: how the process of recording worked and how and why the technologies that were so important to that process were utilized. Plus, we will also discuss the products that engineers use to record the great popular music that we have come to love and to cherish. Without further ado, the first series of articles will focus on the types of processors that were used to record, mix and master the great music of the past. There are three types of processors: spectral processors (equalization units); timing processors (reverb and delay units) and amplitude (or dynamics) processors (compressors, gates and limiters). This article will discuss both microphone preamps and direct box units. Microphone preamps and direct boxes are essential components for the recording process. In fact, these units are critical to excellent recordings, but their importance is often overlooked. But, the question is, “How did the legendary recording studio engineers of the past use them?”

What are microphone preamps?


Let’s just put it simply, microphone preamps are devices which allow you to take the signals from what a microphone hears or picks up, so that they can be recorded into either your software program or recording device. That’s it! These amazing devices are not complicated at all. In fact, there is also nothing complicated about using one of them either. It should be noted that the majority of the time, professional audio equipment is actually very easy to use. It is my belief that sometimes engineers scare people who are not involved in making music away from it, by inventing a complexity that is really not there at all. Each of the devices that you use for podcasting, recording your voice on your smartphone or in playing a part in a public address announcement, all make use of a microphone preamp. Turning it up, so that you can hear yourself without clipping, distortion or picking up unwanted sounds or noises is the key to operating one effectively outside of a recording studio environment and in one, too. 


In the beginning, microphone preamps were completely intertwined with the history of audio itself. In fact, these devices date back to the invention of the microphone– not in the 1920s, but in the 1870s. The origin of the microphone, as we will explore later, is shrouded in mystery, with several imminent engineers and inventors laying claim to its creation, including: Emile Berliner, David Edward Hughes and Thomas Edison. It’s safe to say that each of these notable engineers and inventors created the device that we think of as a microphone at roughly the same time– around 1877 and that invention was inspired by another revolutionary innovation of the time– Alexander Graham Bell’s telephone in 1876. While the ability to hear microphones, use speakers and broadcast music existed by the 1920s, it was during this decade where a true push to create standalone microphone preamps to supplement the burgeoning radio broadcast and music recording industries began with such companies as RCA (in the United States), the BBC (in the United Kingdom) and Telefunken (in Germany) (among others) being early pioneers in this process. It was an important component of the early history of professional music recording. By the close of the Second World War, with the growth of vacuum tube technologies, and an interest in the recording of audio for music, film and broadcast, microphone preamps became one of the first components of the professional audio world to undergo rapid development. This development would see the microphone preamp transition from being stand-alone tube-based units to becoming the integral component to the development of the first consoles for music, film and broadcast. 


As solid state technologies developed by the mid-1960s, microphone preamps became smaller in size and found themselves as a part of the growing large-format console revolution. At first, as consoles were made by custom designers for recording studios (or in the case of Dick Swettingham at Olympic Recording Studios in London and the engineers at EMI, now Abbey Road, were made by the engineers as custom designs by the studio engineers themselves), microphone preamps for the very first time became the integral component of the channel strip– enabling multiple sound sources to be recorded at the same time. One company in the United States which pioneered this concept was Electrodyne which created the components for channel strips which could be installed in console frames or housings. Other early pioneers in this field included Spectra, Flickinger, Helios and Sound Techniques (among others)-- and by the late 1960s and early 1970s other companies which produced them, a few of which are dominant leaders in the field today, such as API, Neve and Trident emerged. As the popularity of these consoles and their modular preamp and equalization and dynamics (later) sections became staples of the music recording industry, engineers and producers who wished to carry their own units with them inspired the creation of stand-alone units and modules, some created by boutique manufacturers for the first time, while others simply racked-up the consoles modules which possessed their favorite sounds and carried them with them from studio to studio which became a hallmark of the industry by the mid-1980s that has continued into the present. 


In fact, most of the legendary preamps which you still find in modular form today including the (AMS-Neve) Neve 1073®, (API) API 312, and the (Trident Audio Developments) Trident A-Range came from this period, as did the fine boutique preamps that are available from such companies as John Hardy, Grace Designs, Manley Labs, George Massenburg Labs and Millennia Media Systems. Today, you can also find preamps that were inspired or are authentic versions of the preamps from the early days of the first large-scale consoles from such companies as Spectra1964 (Spectra), H2Audio (Helios), Skibbe Electronics (Flickinger) and Pete’s Place Audio (Electrodyne), as well. Microphone preamps come in a variety of forms: 500-series modules, rack-mount units and even as 80 series modules. They can be found on hardware interfaces, consoles and in rack-mount units. In addition, microphone preamps can be found in single-channel versions and in a few cases, you can find them in rack-mount units which feature up to 8 preamps. While preamps come in so many different versions, each of these units are incredibly easy to use. With such an array of amazing technologies available today in the world of professional audio, the question now becomes, “How do they work?” In the next section, we will discuss how to use a legendary microphone preamp for music recording– the Focusrite ISA microphone preamp. 

How do microphone preamps work?


While preamps come in so many different versions, each of these units are incredibly easy to use. Microphone preamps typically have the following functions that you can select, including: gain, pad, polarity, output and phantom power. The gain function simply allows you to boost the volume of what the microphone is able to pick-up or hear from your source (reproduce). The pad function is a protective one– which allows you to dial down an overpowering signal coming from your microphone on a very dynamic or loud source. Most of the time, preamps allow you to have a 20db pad or cushion. Some preamps also feature overload indicators, normally a red light which will illuminate if it is being overloaded. Also, most of the time, legendary preamps, conversely allow you to have more than 60db or gain, or boost for reproducing what your microphone is able to hear, or pick-up from a source in the studio. The polarity function allows you to reverse the polarity of a signal. It is rare that you should have to use this function, again it is another fail-safe switch. A solid understanding of fundamental microphone technique and use can eliminate the need to use either the pad or the polarity functions on a preamp. Some preamps also feature an output switch that will allow you to use a transformer to either increase or decrease the amount of gain that can come from the unit. 


It is rare to find a microphone preamp which does not offer a 48-volt phantom power function or switch. Phantom power is essential for the use and function of condenser microphones which require it to boost their signals to a proper level. Dynamic, ribbon and tube-based condenser microphones do not require phantom power and switching it on while using one of these microphones may cause severe damage. If you are using a condenser microphone, you should make certain that each of the components of your signal chain are properly connected before switching it on, otherwise it could lead to severe damage to your equipment. However, if each part of your signal chain when using a condenser microphone is properly connected, you will hear the smooth signal of a condenser microphone through the use of a legendary microphone preamp.


Microphone preamps are easy to use and can be effective recording tools for engineers if just a few simple guidelines are followed:


1. Use solid microphone technique to record your sources. If you place a microphone where it can be damaged, it may damage the preamp, as well.

2. Make sure that you are knowledgeable about the microphone that you are using with your preamp. If it is a condenser microphone, it will require phantom power. If you need to use phantom power, make sure that each component of your signal chain is connected properly prior to switching on phantom power.

3. I often read or hear about engineers driving a particular preamp or pushing a unit very hard to achieve a certain type of tone. I never saw an engineer drive a preamp to distortion. In fact, I saw the opposite. I saw amazing engineers use excellent microphone technique combined with excellent preamps to achieve beautiful recordings. 


Great engineers use their equipment wisely and so should you. In fact, I have seen engineers repeatedly use preamps that are more than 40 years old that still sound phenomenal. If you use your excellent preamps wisely they may be one of the best investments you will ever make for your recording studio facility. All of this begs the question, “How did the legendary recording studio engineers of the past use microphone preamps?”

How did the legendary recording studio engineers of the past use microphone preamps?


Microphone preamps have never been complicated to use and their function has actually changed very little over time. However, their importance has always remained a constant for legendary recording studio engineers. The right microphone preamp can make a true difference in the sound of a recording. This fact is because all microphone preamps, just like the microphones that they work in tandem with each have their own unique sound. For example, an API 312 preamp will not sound like a Neve 1073, or a John Hardy M-1 or a preamp from Millennia Media Systems for example. Though each of those units listed above are examples of amazing preamps, each one has a different sound and would be used by legendary recording studio engineers for a very different purpose. I have seen legendary recording studio engineers use the API 312 for drums, the Neve 1073 on electric guitars, the Hardy M-1 on vocals and bass guitar and the Millennia preamps on both a grand piano and an acoustic guitar. Though these are not the only uses for these amazing preamps, it does give you a sense of the fact that each one brings something unique to the table with the way in which they quite literally deliver a sound for the purpose of recording great music. 


I will repeat this statement from earlier, I never saw an engineer drive a preamp to distort or to have a sound that was not in keeping with its original design. In fact, I witnessed the opposite and in my own use applied them in an opposite fashion, as well. Most of the great engineers used microphone preamps because of their natural sound and used them to create solid tracks, not for experimentation. Distortion was always treated as an effect that could and should be applied later– during the mixing process, rather than while recording solid tracks, or came from the musician and was recorded using the preamp, but without overloading it, or driving it in a manner that would not have been consistent with its normal use. Preamps are such a critical component of the recording process, as are the microphones which they work in tandem with, as mentioned above. There is never a reason to overload either of these critical components of the recording chain– certainly not when these effects could and should be applied later in the music-making process. It is also worth noting that each of the legendary engineers that I worked were careful in applying the use of phantom power as well. 


What are some of the microphone preamps that would have been used by the legendary recording studio engineers of the past that are still available today?


AMS Neve 1073 Range

API- 312 (500-series module)

Spectra1964- STX 100D

Millennia Media- HV-3D (8-Channel)

John Hardy- M-1 (4-Channel)

H2Audio- 2128 (500-series module)

Chandler Limited- TG-2 (500-series module) 

Pete’s Place Audio- Electrodyne- 501 (500-series module)

Grace Designs- M801 (8-Channel)

Manley Labs- FORCE (4-Channel)


** Special Note– All 500-series modules require a compatible 500-series chassis (or rack) for you to be able to use them. The 1073® is a registered trademark of AMS Neve Limited.

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