History of the mic preamps

(from the VT-1/VT-2 Instruction Manual)
One day in 1991 I was going through some old masters in a closet at home and came across a reel from 1968. It was one of the first studio recordings I ever made. I pulled the tape box off the shelf and thought about those days. Although I suspected that the recording might be a bit crude, I remembered that the music was pretty good, so I made a cassette to listen to in the car.

I kept forgetting to put the cassette in my pocket for a few days, but finally I remembered to take it. That old recording brought back memories of my first studio — and how primitive a setup it was. But listening to that tape was a revelation; some of the sounds were really nice. The vocals were full and warm but still punched through. Acoustic guitars had a depth I don’t often hear in current recordings. And the sax solo — wow! It ripped through with a grossly distorted but beautifully powerful sound.

That recording was done on a 4-track Scully 280 and mixed to a 2-track Scully. My prize microphone was a Neumann U-87 and that’s what was probably on the featured instrument or voice on each track. Nothing too unusual about that.

I couldn’t afford the Electrodyne board of my dreams back then. In fact, I built the “mixer” myself. It consisted of half a dozen RCA tube microphone preamplifiers that I salvaged from the junk pile of the radio station where I worked, an equal number of old Daven rotary faders, and key switches that “panned” the output to left, center, or right.

It was the tube preamps that made that recording sound so good. There was no EQ, no reverb, but maybe just a touch of compression on some sounds, from an old RCA broadcast type (tube) limiter.

Those preamps were 1940s vintage. They used octal metal tubes with a shielded grid cap, a cylindrical output transformer the size of a coffee can, and a huge power supply on a separate chassis. They were a lot of trouble — the tubes were microphonic and the output was often noisy. In addition to the hums and hisses, occasionally a take would be ruined by crackles and bangs from the tubes. I couldn’t wait to get rid of the things.

And so I did, not long after. I got a beautiful console with IC op amps, linear faders, real pan-pots, echo sends and returns, and EQ on every input. No more noisy tubes for me.

But now, 25 years later, I got to thinking about the sound of those tubes. Hit them with a bit of excessive level and the sound became real fat. Hit them with just the right level and they sounded warm and intimate.

Could that sound be duplicated today? I dug out my old RCA Receiving Tube Manual, Radiotron Designers’ Handbook, and several editions of the ARRL Radio Amateur’s Handbook and reviewed the vacuum tube theory I hadn’t thought about for years. A quick check in the supplier’s catalogs confirmed that tubes were still easy to obtain.

Over the years much has changed in the world of electronic components. Were the necessary parts still available? I found out that they were (though not necessarily cheap), and, in many cases they were vastly better than the components available back in the age of vacuum tubes.

Carbon resistors could be replaced with quieter metal film types. Sonically superior polystyrene and polypropylene capacitors were preferable to the old paper types. The power supplies could be solid state — and easily regulated. Electrolytic filter capacitors were smaller. The only parts that remained to be found were top quality audio transformers that matched the tube input and output impedances.

A call to the great folks at legendary Jensen Transformers revealed that not only were the necessary transformers still available but that they were orders of magnitude superior to the technology of the 50s and 60s.

A couple of months research into the classic tube mic preamp designs gave me a good idea of how to proceed. A breadboard prototype was constructed and tested, and it worked great! (Although the open construction resulted in some RFI: while experimenting with different component values one night with a pair of headphones on the output, I heard a half hour of Radio Havana coming through weakly but clearly.) Professional quality specs on frequency response, distortion, noise, phase shift, and so on were definitely attainable.

Now it was necessary to squeeze the last dB of performance out of the circuit. Computer circuit analysis was one tool not available to the designers of the original equipment, and it was amazing how careful manipulation of values could make a significant improvement in performance.

The next prototype was built and its performance was even better, largely because of better shielding and a better layout. This one became the testing ground for additional experimentation. There is not a single component in that prototype that hasn’t been changed in an attempt to improve performance. Some parts of the circuit have been through dozens of iterations. Modern test equipment can quantify and graph parameters much more quickly than could be done by hand-plotting back in the heyday of “hollow state.”

This prototype became my preamp of choice for all my recording. I used it (and a another one I built soon after) for a year of location recording, mostly of classical and choral music, but also for studio sessions. Although I have some very fine commercial and home built mixers, after using the tube preamps, I just couldn’t bring myself to use the solid state preamps anymore.

Why do tubes sound better? All properly designed audio amplifier circuits exhibit low distortion throughout their operating amplitude range. The difference in sound is evident when the circuit runs out of headroom. Solid state devices tend to abruptly transition from low distortion to extreme distortion (clipping). This is a good trait, since when operated right up to their maximum level solid state amplifiers can maintain excellent performance. Digital audio circuits have similar characteristics.

It’s the nature of the distortion that makes tubes sound different. Solid state circuits run out of headroom when the output voltage exceeds the power supply voltage. The result at this point is gross distortion — the output becomes a square wave. Square waves are not found in sounds that we usually consider musical, so our subjective response to them is negative.

When a tube circuit distorts, the primary distortion product is even order harmonics, with the second harmonic dominant. It so happens that musical instruments also produce primarily even harmonics. By definition, that’s what makes them “musical.” So you could say that tube circuits can add a musical component to recorded sound. Fortunately, you can take your choice — keep the level reasonable and obtain good clean audio, or run the circuit into distortion and generate some harmonics that weren’t there to begin with.

One factor that is often underestimated is the actual peak level produced by a microphone, especially in close-micing situations. Peak output can easily exceed 1 volt! The duration of these peaks is often very short, but an overloaded solid state amplifier will change the character of the sound significantly during the peak. Vacuum tube designs may also overload on the peaks, but the resulting distortion is much more acceptable to the ear.

There may be other factors at work, too, that make vacuum tube amplifiers sound different, even when operated in the low distortion part of their range. I have not proven any of these esoteric theories to myself yet, but I think they have merit. Here’s one: perhaps the minimal number of active devices in the signal path makes a difference. My preamp has only four active devices, while even the simplest solid state op amp circuit may have dozens.

But back to the story ….

Finally the preamp was ready for some serious testing in the real world. A number of friends in the music business, both musicians and studio owners, were intrigued with the possibilities of this device, so it was easy to get volunteers to test, evaluate, and give me additional input on the performance. This resulted in a few more changes which have been incorporated into the final design.

The VT-1 represents, I believe, the best performance attainable with this type of circuit. And it sounds as good as or better than any of today’s top-of-the-line solid state designs, along with all the sonic advantages of tubes. Not only that, but it is built to last. Solid construction is used throughout, and only the best parts are used, many of them Mil-spec.

I have found over the years that one insidious source of distortion in the recording studio comes from connectors, switches, relay contacts, patch jacks, etc. Although these connections may be perfectly adequate when new, after a period of time the contacts oxidize and the sound gets a little dirty. Individually they may not cause much of a problem, but put your audio through a few of them and you will start to hear the degradation.

To avoid this, the VT-1 design eliminates as many of these trouble-prone connections as possible. In fact, the only non-soldered connections from input to output are the input select and phase reverse relays (which are gold-contact, sealed, instrumentation type) and the tube sockets.

SO, DOES THE VT-1 DUPLICATE the sound of my old tube preamps? No, not exactly. Gone are the hum,hiss, crackles, and bangs. And although I don’t have the old preamps to do an AB comparison of the sound, I am certain that the better modern passive components give the VT-1 a superior sound. The VT-1 has been used for all types of recording — vocals, announcers, acoustic instruments, electric instruments, classical — and it works well with them all.

The VT-2 was developed in 1995 in answer to requests from a number of our customers for a two-channel version of the preamp. The VT-2 occupies the same amount of rack space, but is four inches deeper than the VT-1.

Douglas W. Fearn

August 1992 (Updated July 1996)

West Chester, PA

Original company history

The history of D.W. Fearn & Associates is the history of its founder, Douglas W. Fearn.

I have always been interested in both music and electronics. As a youngster, I would often go with my father to rehearsals, concerts, and recording sessions of the Philadelphia Orchestra, where he played French Horn. The experience of listening to one of the world’s finest orchestras in a fine concert hall shaped the way I hear things. I would often wander around the Academy of Music in Philadelphia during rehearsals and listen to how the orchestra sounded in many different seats in the hall. Or, I might sit on stage with my father during a rehearsal and experience what it is like to be surrounded by pure acoustic music.

At the same time, I was fascinated with electronics and built many devices for fun. As a young amateur radio operator, I built transmitters and other rf gadgets. Later, I built audio amplifiers. This was in the 1960s, when transistors were readily available but expensive and they didn’t sound very good. So virtually all of my experience in those days was with vacuum tubes.

My high school had an FM broadcast station, and I was very active in operation and construction of new facilities there. The radio station recorded and broadcast many school events, including concerts. We were fortunate to have some very fine equipment: Ampex tape machines, Collins consoles and mixers, and an assortment of dynamic and ribbon microphones. Often friends in rock bands would ask me to make a tape for them, and this led to my desire to operate a recording studio.

While still in high school, I worked as a part-time engineer at WPEN in Philadelphia. I continued to work there for a number of years while saving money and collecting equipment for a recording studio. In 1973, I left the station to devote my time entirely to Veritable Recording Co., which I started in 1969.

The recording experience taught me what it takes to obtain good sound, and part of that quest led me to design and build some of my own equipment. It was from that experience that the VT-1 Vacuum Tube Microphone Preamplifier was born in 1993. Except for occasional location recording, my time is now devoted full-time to manufacturing the preamps and developing new products.

The first twenty preamps were built by me, but now all the assembly is done for me by a couple of perfectionist engineers. I continue to inspect each one upon completion, and I do the final measurement tests and the listening test .

I started the business working from home, and when the business had taken over far too much of our house, my wife and I designed a new house with facilities to accommodate the growing business. Rather than “working at home,” I think of my life as “living at work.” We are located about 25 miles west of Philadelphia in Chester County, Pennsylvania. I work with views of woods, horse farms, and the Brandywine River.

I am still enthusiastic about Amateur Radio, and operate using Morse Code exclusively; ironically, there are no microphones connected to my amateur radio equipment. Most of the equipment is restored 1950s vintage all-tube gear. I am also a licensed private pilot with instrument rating, but all the electronic gear in my airplane is solid-state.

Most of my recording these days is classical or choral live performances. I typically use an AEA R88 as the main pickup, with Coles 4038 ribbon spot mics, and B&K 4007 omni mics wide-spaced to add ambience as needed. All mics go through VT-2 preamps direct to a RADAR at 24/96, or, when practical, to a Studer A810.

Why Vacuum Tubes?

By Douglas W. Fearn

(reprinted with permission from Pro Audio Review, Jan/Feb 1996)
For some of us in audio, tubes never really went away. We go back to the days when all equipment was tube equipment. (My first job, in the late 1960s, was at a Philadelphia radio station that was 100% “hollow state” from microphone to antenna.) I admit that I was thrilled when the first solid-state tape machines and recording consoles appeared, even though they didn’t sound as good as the old tube gear they replaced. The features were dazzling, so many of us were willing to tolerate a grungier sound, or pretend we didn’t hear it — at least for a while. (Sounds sort of like the digital vs. analog controversy now raging in some circles, doesn’t it?)

It seems that many of us who used tube gear in the past, and a growing segment of younger engineers and producers, have (re-)discovered tubes. Do they really sound better, or at least different? And if so, why?

Much (and maybe all) of the answer is contained in a paper in the May 1973 Journal of the Audio Engineering Society by Russell O. Hamm, Tubes Versus Transistors — Is There an Audible Difference? The quotes in this piece are from that article. Hamm found that the output level of studio microphones under typical recording conditions contains peaks far in excess of what VU meters display. Everyone knows that, but the peaks, as measured with an oscilloscope, are really high, easily exceeding 1 volt! The tube or transistor used in a condenser microphone, or in a microphone preamplifier, often will be driven into severe overload by these peaks. The peaks are short, so the sound isn’t grossly distorted-sounding; but the distorted peaks do affect what we hear. All preamps (and condenser mic electronics) are overloaded by these peaks, but tubes handle it differently than solid-state devices.

When transistors overload (in a discrete circuit or in an op amp), the dominant distortion product is the third harmonic. The third harmonic “produces a sound many musicians refer to as ‘blanketed.’ Instead of making the tone fuller, a strong third actually makes the tone softer.” On the other hand, with tubes (particularly triodes) the dominant distortion product is the second harmonic: “Musically the second is an octave above the fundamental and is almost inaudible, yet it adds body to the sound, making it fuller.”

There’s a lot more revealing information in Russ Hamm’s paper, and if you want more details about why tubes often sound better, it’s worth finding a copy.

Another difference between tubes and solid-state devices (including FETs) is the load they provide to the source. This is particularly significant with condenser microphone capsules. Even though an FET has an input impedance similar to tubes (in the megohms), for some reason condenser elements just sound better going into a tube. Is it input capacitance? Or some sort of dynamic loading factor?

If you ask enough people (particularly audiophiles), you’ll start to discover some truly metaphysical theories on why tubes sound better. Some explanations utilize quantum theory, some are simply wrong, while others are just plain bizarre. But in my own circuit designs I’ve encountered some odd phenomena that I can’t explain. For example, in a mic preamp prototype, I discovered that performance measurements were different if the unit was upside down. After I tried to eliminate all possible environmental factors, the difference persisted, even with a variety of tubes, and in different buildings. It was audible, too, though subtle. Was it caused by gravity slightly shifting the internal tube elements? The earth’s magnetic field? I still don’t know.

Tubes sound better because their distortion products are more musical. Tubes provide a more appropriate load to transducers. Those are the fundamental reasons why tubes sound better, but is there more?

New Owner

D.W. Fearn Licenses Hazelrigg Industries to
Manufacture and Market the VT Product Line

The arrangement allows D.W. Fearn founder Doug Fearn to devote more time to designing new products

West Chester, PA – D.W. Fearn, a leading manufacturer of professional vacuum tube audio recording equipment, recently announced that as of January 1, 2017, production and marketing of its iconic line of gear with the distinctive red front panels will be handled by Hazelrigg Industries under an exclusive licensing agreement. D. W. Fearn President and founder Doug Fearn will continue to design new products and will serve as a consultant to George and Geoff Hazelrigg. This is not the first time that the two organizations and the three men have collaborated.

“I have complete confidence that George and Geoff will do right by the products and our customers,” said Fearn. “We three share a similar audio philosophy and approach to sound recording, as well as a shared history. I designed the amplifier and power supply for their VLC-1 channel strip product, Geoff worked for me as an assembler of D.W. Fearn gear, and he and George have participated in recording sessions in my studio.” All three are pilots.

In addition to running their manufacturing company, the Hazelriggs also are accomplished musicians, with Geoff on upright bass and George on keyboards.

“My brother and I are intimately acquainted with D.W. Fearn gear and are happy to embrace the awesome responsibility of making these critically acclaimed products available to the recording public,” said Geoff Hazelrigg. “We are working closely with the D.W. Fearn dealer and vendor network to ensure that current and future customers experience no interruption in service or support.”

Also Available

 

The Red Legacy

 

The D.W.Fearn Legend

a film by Alain Le Kim
from the Soundstrips description:

“Just building a tube thing on a printed circuit board didn’t appeal to me. I just liked the idea of the old fashion way of building it on a metal chassis. And that’s the way I designed it to be built. And I came to the realization later that doing things with point-to- point wiring allows you to build things in three dimensions. The less tortuous you make the path, the better things work.”

Alain Le Kim is a French documentary film maker and photographer. He also appreciates fine equipment, whether it is a camera, a microphone, or audio electronics. This prompted Alain to make a series of documentary films about some of the audio equipment designers he has encountered in his travels around the world.

Alain spent two weeks living with us while making this film. For someone like me, who has been a “behind-the-scenes” person all my life, the idea of being the subject of a film was somewhat uncomfortable. But Alain’s relaxed style, along with his passionate interest in the world of audio, made the process very easy for me. Although I still cringe at some of the things I wish I had explained better, I am pleased with film that Alain made.

Please don’t stop at “The Red Legacy,” however. Alain has made films about many fascinating people, many of whom are friends of mine. Watching Alain’s films, I learned new things about people I had known for decades.

Be sure to take a look at Alain’s photo galleries as well. His pictures are the work of a true artist.