The SYNCRØN Model AU-7a FET cardioid condenser microphone Plus information on the Fairchild F⁄22 and the Syncron S-10
The following text is from the Syncron Corporation AU-7a marketing and speciﬁcation sheet, which is downloadable below. This is the ﬁrst really self-contained condenser microphone (no awkward power supply to contend with). Over 2500 hours of battery life through the use of standard, low-cost Mallory mercury cells. Cardioid pattern, oﬀering a front-to-back ratio of better than 20 dB, makes the AU-7a well suited to diﬃcult sound pick-up tasks including high-quality public address systems. Rugged Mylar diaphragm provides smooth frequency response with total absence of annoying peaks. Single transistor ampliﬁer, built with missile-grade components, assures high reliability in the ﬁeld. The entire ampliﬁer module is potted in silicone rubber to protect the components against shock and moisture. Low noise and distortion plus high output level give maximum sensitivity and outstanding clarity of sound. The balanced output of 50 or 200 ohms is easily interchangeable by means of miniature patch cords with gold-plated plugs. The AU-7a connector is multi-pinned, and functions as a switch to turn the microphone on and oﬀ. There is no possibility of leaving it on when not in use. The multi-pin connector is also designed to provide for an auxiliary power supply for continuous operation. Built-in swivel permits tilting through 130 degrees.
Frequency Range: 30-18,000 cps, ±2.5 dB
Directional Characteristics: Cardioid, 20-dB front-to-back ratio
Output Level: −45 dBm (referred to 10 dyne/cm²)
Distortion: Less than 0.5% at 100 dyne/cm²
Equivalent Noise: Less than 20 dB-SPL
Battery Life: 2500 hours
Weight: 1 lb. 7 oz.
Price: $169.50 (Price shown for historical purposes only. These mics are not for sale.)
Excerpted from the Syncron AU-7a booklet, available for download below
Output Level: The microphone output, when subjected to a 1,000 cycle sound pressure level of 10 dynes per cm², and with the mic terminated in a non-inductive, resistive load equal to its rated impedance is –50 dBm. A 10 dyne per cm² sound pressure level is the standard used for rating most low-impedance mics, and is roughly equivalent to the average sound level of a symphony orchestra as heard from front row center.
Directional Characteristics: The AU-7a has cardioid pickup patterns as shown above in Figure 2. The generating element uses two aluminized Mylar diaphragms. Only one of these is electrically connected. There are acoustical phase shifts between the diaphragms, causing the element to be half pressure responsive and half pressure gradient responsive. The sum total of these characteristics results in the familiar cardioid response, having a front to back ratio of 20 dB. The front of the microphone is indicated by the colored dot at the bottom of the screen.
Frequency Response: On-axis frequency response of the AU-7a is linear ±2.5 dB from 30 to 18,000 cycles per second. A machine-run response curve on a typical AU-7a in an anechoic chamber is shown below.
View or download a larger copy of this microphone’s unique frequency response graph.
Download a zipped archive of this booklet. Printing instructions are included. (1.2 megabyte PDF)
During May of 2007 an eBay auction appeared for a Fairchild F⁄22 microphone. Photos are below. While the auction was active, someone sent the following italicized message to the seller:
This mic is also known as the Syncron AU-7a made in Wallingford CT between 1965 and 1966. Syncron was an original equipment manufacturer for Fairchild. It is a single FET mic that was the ﬁrst commercial product made with an FET. I wrote an article on the successor to the AU-7a, the S-10, in EQ magazine in 2002 I think it was. Earlier, there was an article on the F⁄22/AU-7a. I own three of the F22s. There are no schematics. I know all this because I worked in the building where the mics were made and the designer was my ﬁrst boss and mentor. —From an unidentiﬁed eBay subscriber in 2007
OCTOBER 2008 UPDATE: The Web is an amazing resource. A serendipitous eBay encounter with Mr. Richard Tyler resulted in his introducing me to Mr. William Hennessey, one of the original Syncron Corporation employees. Of course I jumped at the opportunity to ask Mr. Hennessey about his association with the company, beginning with a question about a rumor that a recording studio now occupies the building where Syncron was located. What follows are Mr. Hennessey’s recollections, which I greatly appreciate his sharing. Thanks also to Mr. Tyler for introducing us. —S. O. Coutant
First: there IS a recording studio presently on the site of the original Syncron facility. It may even contain a large anechoic chamber that was constructed there for testing microphones… although of that I have no current knowledge. The studio is known as Trod Nossel Productions and is owned by the family of the late Dr. Thomas Cavalier, a dentist who was a Syncron stockholder. Syncron was involved in numerous projects, and the studio was an oﬀshoot that survived its demise, following foreclosure by a nearby lending institution which is also extinct.
In addition to the recording studio, Syncron was in the business of buying and leasing motion picture equipment, in hopes of supplying services to Hollywood type ﬁlm productions when shooting on-location scenes in the Northeast. In short, Syncron got involved in too many ancillary activities instead of concentrating exclusively on its primary mission: making microphones. (There were only two models—the AU-7a and the S-10. Each was constantly undergoing steady improvements before being marketed, and the resultant lengthy lead times consumed most of the start-up capital. The helter-skelter nature of Syncron’s various ventures contributed to its eventual collapse, during which period the recording studio was spun oﬀ to the Cavalier family.)
But that’s the END of the story. Here’s the beginning.
William Lobb, an Air Force veteran who became an engineer at WTIC (Hartford), was the genius who designed the AU-7a and the S-10. He had learned of Field Eﬀect Transistors and was a busy “tinkerer” at his home in Wallingford, Connecticut. He admitted to being aware of preliminary designs created by Steven Teachout (of a company named Teachout West), but Lobb advanced Teachout’s schematics to create a then-revolutionary self-contained condenser unit that used a self-polarizing battery. As I recall, the batteries were obtained through military surplus, having initially been utilized in underwater mines by the U.S. Navy. Lobb apparently designed something never-before produced commercially. The mic was as convenient as any of the highest-quality condensers then available. When ﬁnally marketed, it sold for $169, compared to the $500-to-$600 models oﬀered by Neumann, Telefunken, and/or Sennheiser. The even more expensive best-of-the-line model, made by B&K (Brüel & Kjær), was not widely used. The Syncron anechoic chamber contained one for comparison tests! Lobb was always proud of the results: the AU-7a measured up to the B&K very favorably.
Prior to joining WTIC, Lobb had befriended a fellow Airman named John E. Frechette, a Philadelphian who had enjoyed modest success as a ﬁlm producer. Frechette had returned from supervising an overseas documentary which employed top European personnel (even The London Symphony!), and he and his young family settled in Wallingford to renew ties with Lobb. Together they conceived the idea of manufacturing and marketing the revolutionary new microphone.
And that’s where I entered the picture. I was a staﬀ announcer at WTIC, working closely with Lobb on many on-air programs. I became excited about the microphone project and teamed up with Lobb and Frechette in promoting the idea. Lobb left WTIC to devote full time to the ﬂedging ﬁrm, and later I joined too. We were three young guys with lots of enthusiasm and energy—but absolutely NO business sense. Friends and relatives purchased stock; a local bank provided ﬁnancing. We rented an old small-factory building in Wallingford; expanded into audio-related ventures (like the anechoic chamber, recording studio, and ﬁlm equipment)—and proceeded to endure for nearly three years before ﬁnally going bust. Frechette had convinced Sherman Fairchild to add the AU-7a to his hobbyist line of professional audio-video equipment, which explains how the AU-7a evolved into the F⁄22 [photos below]. After Frechette left the company (to resume his ﬁlm career), I was nearly as lucky in convincing RCA to let Syncron make o.e.m. mics under their label. By then, however, our cash ﬂow problems overtook such possibilities and Syncron sank within sight of a safe harbor.
Lobb went on to earn praise as a highly regarded audio consultant, traveling far and wide to advise on construction of auditoria. I got “an honest job” working for the State of Connecticut from which I’ve retired and am now living happily ever after in Niantic-on-the-Atlantic.
I visited Bill Lobb in a convalescent home a few months ago. He’s back in Wallingford, but seriously ailing, with poor eyesight, bad dentures, and progressively worsening health. I doubt if he’ll ever leave nursing care. We reminisced about our old times together at ’TIC, but barely mentioned Syncron (because it’s a painful memory for both of us). I doubt if Lobb gives it much thought these days… and I for one would rather forget that whole episode in my life. But—since you asked—there it is.
I have few, if any, personal souvenirs from the Syncron days. No sample mics; no old recordings or ﬁlms; not much of anything except one sales brochure. In fact, your website contains more materials than my scrapbook! And, as Walter Cronkite would have said, “That’s the way it is…” —William Hennessey
See the Syncron ﬁlm facility during the sixties showing company founders John Frechette, Bill Hennessey, and Bill Lobb. Photo courtesy of Mr. Hennessey.
JANUARY 2009 UPDATE: Syncron co-founder John Frechette has made contact with me. We plan to assemble additional details about Syncron that will appear here. —S. O. Coutant
MARCH 2023 UPDATE: Fourteen years have passed without additional messages having been received by me from the Syncron founders. We are blessed to have as many data as we do. I appreciate every word that has been shared. Perhaps the day will come when a technical journal staﬀ member will come upon this webpage and decide to do something with the information. —S. O. Coutant
A set of the mercury cells, obviously deteriorated. Because of their mercury content and the resulting environmental concerns, the sale of mercury batteries is banned in many countries. Photo courtesy of Audio Engineer Ted Tuthill.
The battery bracket module.
The 21-volt Type 303448 cells and the 4.2-volt Type 303447 cells.
The microphone’s Amphenol receptacle.
The mating Amphenol cable plug is adapted to an XLR.
The Fairchild F⁄22
The SYNCRØN Model S-10
APRIL 2009 UPDATE: Syncron S-10 owner Jeff Scarborough provided us with the following information.
“Some will assume because they have a battery inside that they are a back-electret. No, these are actual condenser mics. The amps are powered by a 9v (originally mercury 8.4v) battery. The capsule is polarized by phantom 48v. Originally the polarizing source for the capsule was a high-impedance 62v source in a cylindrical package, kind of like a battery, kind of like a capacitor. More on that later.
Listen to excerpts of six vocal tracks recorded with these mics.
The size is ⅞" × 7¼" (22mm × 185mm).
“I have learned a few things about these in the several years that I have owned them. I have an original cut sheet for the S-10, and it has Connecticut broadcaster TV personality Bill Hennessey’s business card inside (he was working sales for Syncron Corporation in addition to his other careers). I was able to track him down and traded a couple of emails with him. I have also gleaned information from other sources that have popped up on the web from time to time.
“The S-10 was successful (favored by jazz artists), and afterwards was distributed by Vega of California. They eventually became unavailable: I would think that the polarizing source became unavailable. This high impedance, high-voltage source for polarizing the capsule was to have a lifetime of twenty years, although both of my mics still worked well only ten years ago. A year ago the voltage sources were getting weaker, and I remembered what I had seen on an earlier mission inside these mics: a center tap on the transformer secondary. Perfect. I connected the center tap to the high-ohm resistors that feed the high voltage to the capsule, and they have since worked better than ever on phantom 48.
“My earlier mission inside the mics was just after I acquired them. They were sporting a four-pin XLR, the fourth pin being negative battery out, and when shorted with ground via the four-pin mating female XLR, would supply power to the one ﬁeld-eﬀect transistor ampliﬁer. I opted to change them to a standard three-pin XLR, and simply remove the batteries when not in use. The only other accommodation I have had to make for the mics was the ampliﬁer battery itself. I make a spring-loaded 9v stack of LR44 or AG13 batteries inside a non-conductive tube. They will also work with commercial battery A1611, which is simply a stack of similar batteries inside a tube.
“These simple modiﬁcations have not changed the mics. Everything is still there, including the polarizing 62v Sprague “batteries” inside—I’ve just made the mics usable. And usable they are. I have not heard anything as silky and extended as these mics. They are so forgiving on drum overheads… they really shimmer all the way out without a touch of harshness or clang from the cymbals. They work well on vocals, similarly smooth and articulate, with a big proximity eﬀect within six inches or so. But I have never used them without protecting the capsules completely with small foam head ﬁlters and also a nylon pop ﬁlter when using them on vocals. Overall they do agree in sound with the response graph given in the PDF. Incidentally, I have a favorable evaluation of these mics from Audio Magazine dated June 1966, which you can read below.” —Jeﬀ Scarborough
The following review is from the June, 1966 issue of Audio Magazine
SYNCRØN S-10 CONDENSER MICROPHONE We often speak of the individual character of transducers, mentioning phono cartridges and speakers as typical, and completely forgetting that microphones too belong in that class. They have every bit as much individual personality as any product. And, as is true of all transducers, it is diﬃcult (if not impossible) to laboratory test them and come out with a ﬁrm knowledge of what the product will sound like.
Condenser mics have built a reputation for quality that has set them apart from other systems. If they have become the Rolls-Royce of the recordists, they have also demanded equivalent image pocketbooks. And they have been bulky with their need of separate power supplies.
Transistors have done much for the bulk, reducing the power packs to manageable size and to independence from power lines.
This microphone is not the ﬁrst to be issued that is completely self contained, but it certainly is the most manageable in that it is no larger than many a dynamic. Perhaps even this is not a “ﬁrst” as such. What is dramatic is that the S-10 oﬀers a degree of reliability and dependability that was not available in a portable before. A single replaceable Mallory TR-126 battery is contained within the slim lines of the microphone. Also within is the impedance-matching circuitry. It uses a ﬁeld-eﬀect transistor.
The Mallory battery is only called upon to power the FET. Buried well within the casing is a separate power source that gives the needed 62 volts of polarization to the condenser element. This is a lifetime item. And it should be just that since no current is actually being drawn.
The replaceable Mallory is guaranteed for 1000 hours of operation. We suspect that this ﬁgure is conservative by a factor of many times. Longevity can be further enhanced by simply removing the four-conductor XLR plug between the microphone and the twenty feet of cable. This breaks the battery circuit.
Other mechanical virtues of the S-10 are a weight of nine ounces and a ⅞-inch diameter by 7½-inch length. The patterning of the microphone is cardioid, the diaphragm material is Mylar, output is –53 dBm referenced to 10 dyne per cm² into 200 ohms, and the mic can be operated into any load from thirty ohms to high impedance.
This Syncron handles like a real pro. We were supplied with accessories which include a windscreen ($14.95), a vibration suspension mount ($29.95), and a desk stand ($19.95). The microphone itself with a battery, carrying case, and swivel mount, and with a two-wire shielded cable, sells for $240. Microphones on this site are not for sale.
Tests The best way to test a microphone is to use it. This becomes even more meaningful if it is compared against established favorite units. Frequency response measurements require extraordinarily sophisticated equipment. So we are reproducing the B & K curve tracing that was done by Syncron on this sample. We have no reason to believe that it is anything but accurate.
The Brüel & Kjær frequency response curve of the Syncron S-10.
As would be expected from such a curve, the S-10 is neutral in sonic eﬀect. It certainly does not have that bright rising top end that was so characteristic of the earliest condensers. When we ﬁrst heard playbacks of recordings made with the S-10 we were struck by the general lack of microphone coloration. At the same time, there is no feeling of masking dullness. Rather, the S-10 comes through as a crisp and transparent performer.
With the feeling of independence that the self-contained aspect of this microphone oﬀers, it is easy to forget you are working with a condenser. It goes anywhere with ease. The result for us has been some outstanding ﬁeld recordings with a clarity and depth that we have found impressive indeed. Under the most exacting music applications, the S-10 is easy to get to like. And we do.