Neumann M49

Among the Big Five, the M49 takes a special place. It was the only mic which was never seriously marketed to recording professionals, artists or studios, either in Germany or abroad: entirely a creation by German broadcasters to fit the needs of German, state-owned, broadcast institutions. Consequently, throughout its twenty-year life-span, the M49 remained largely unknown to recording professionals in Europe, and had preciously few private customers in Germany. 

Visually, too, the mic was unusual, compared to its competitors that were marketed to private buyers: an odd-looking, heavy, nickel-plated brass bulb profile sporting a huge wedge-shaped, coarse-mesh basket on top of a disproportionally squat body. This was not most people’s idea of an elegant industrial design. And yet, there is no question that this mic belongs to the Club of Five. The combined intelligence, skill and craftsmanship of the mic’s institutional creators combined with Neumann’s decades-old experience in manufacturing all but guaranteed long-term success for the M49.

Today, almost all M49 ever made bear a Neumann i.d. plate and serial number on their bottom back. Yet, this mic was not conceived at Neumann’s facilities in Berlin, but was initially developed in Hamburg under the leadership of Dr. Herbert Grosskopf at the IRT (Institute of Broadcast Technology) laboratories housed in the NWDR (Nord-West Deutscher Rundfunk). The NWDR was one of several government-subsidized broadcasters founded and established after the war in most of the Federal Republic’s states by the Allied Forces. These broadcast monopolies were only expanded by the government in the 1980s when, for the first time in Germany’s history, privately-owned broadcasters could apply for a license.

Just as before and during World War Two, the power and purse of public broadcasters quickly became the focus for the efforts of most professional audio manufacturers, small and large, in the years immediately after 1945. The IRT developed compliance standards for any piece of hardware that could be used in any of the broadcasting studios throughout West-Germany and West-Berlin, and, through generous public financing, these state-subsidized facilities had cash to invest in research and development. The NWDR, the largest sponsor and incubator of broadcast technology in post-war Germany, attracted a critical mass of inventors and small manufacturers through its financial generosity. That in return rapidly advanced the designs of audio equipment towards the precise and exacting specifications demanded from public broadcasters.

The M49 was one of these government-sponsored developments. Grosskopf and his NWDR team finished the design for this large diaphragm successor microphone to the U47 around 1948/49, and soon thereafter, its revolutionary small diaphragm-in-a-sphere sibling, the M50. Few of the witnesses directly involved during that time are alive anymore, but through earlier interviews and conversations with some of the last employees still around, it is safe to say that Hiller, Schoeps, Maihak, Neumann, and others versed in the manufacture of tubes, transformers, capsules and associated specialty components and circuitry were bidders and/or eventual suppliers to the M49 which was to become the principal recording microphone for voice and music in all of German broadcasting. 

It was of paramount interest for Grosskopf and his team to miniaturize and improve the performance of tubes used in microphones of the next generation. The overall dimensions had to come down-physically smaller microphones with better frequency response, lower microphonic tendencies and better noise floor were needed. Albert Hiller, an electronics specialist with vast knowledge of vacuum technology, had set up shop not far from the NWDR’s lab and offered his services. Initially, he and his small crew of specialists also re-sputtered (i.e. deposited a conductive gold layer onto plastic membranes in a vacuum chamber) defective capsules from pre-war Neumann “Bottle” mics. However, it was Hiller’s tubes which opened the door to miniaturization of microphones. With the institute's generous advance payment for 1000 pieces, Hiller developed the MSC 2, the first truly sub-miniature triode tube of smallest dimensions and highest quality for its time. The tube’s size- about the length of half a human thumb- would make it possible to develop miniature microphones for broadcast use, with an eye towards greatly improved transmission quality, via FM in the near future. And television, the new broadcast medium which had recently been introduced across the Atlantic, was only a few short years away from sweeping across Germany and Europe.

Martin Schneider, development head at Neumann noted in a recent email to me that the patent for remote controlling patterns in condenser microphones - a revolution in pattern control- was filed by the NWDR's Dr. Grosskopf in February of 1949. According to Scheider, the patent was published in 1954 and granted in 1955. The right to produce these microphones was granted by Grosskopf to Neumann by license.

There are still a few very early non-Neumann M49 prototypes with parts from several other manufacturers in circulation. Common to all of them, including the serial version eventually launched by Neumann, were the wedge shaped basket, to avoid standing sound waves between basket and capsule diaphragm, and the compact, perpendicularly arranged amplifier board.

The first specimens were built and shipped in March of 1952. Neumann used the trusty M7 PVC capsule which, together with capacitors, resistors and wiring was borrowed from U47 production. 

Hiller from Hamburg supplied its MSC2 tube only for the first three years of the M49‘s run.

Two reasons contributed to the early demise of that tube. Martin Schneider copied me correspondence from 1952 detailing on-going instability of the direct-heated MSC2: sudden voltage spikes could deteriorate the tube's noise floor or break the heater filament altogether. Neumann’s close relationship with its part-owner, Telefunken, was probably the other reason that Neumann commissioned, and Telefunken developed, yet another microphone-specific tube after the VF14: the AC701k- a refined, indirect-heated sub-miniatutre triode that was even smaller, and certainly quieter than, the MSC2. Its reliability was further refined in 1958. (‘k‘ stands for ‘klingarm‘ - low microphonics. The 'k' suffix was eliminated in the final series of the AC701, when refinement of manufacturing tightened tolerances sufficiently render all of them "klingarm".)

This new, entirely hand-manufactured, tube would soon become the “little engine that could”- not only did it power the M49 and M50, but this sub-miniature triode would remain the only microphone tube accepted by German broadcasters, regardless of microphone brand, until the end of the tube era, in the mid-to-late 1960s.

Around 1954, the AC 701 was ready for serial production and found its home in Neumann’s new small diaphragm mics. The AC701 allowed for a new level of microphone miniaturization and immediately replaced the MSC2 in the M49. That mic’s features remained unchanged, aside of slightly different supply voltages and corresponding components, and an improved transformer optimized for the new tube’s output impedances, until June 1957 (transitions in manufacturing periods always make it hard to pinpoint an exact date of change with accuracy, as mics would be shipped to different clients at different times.) In that year, the M49 'b' version was introduced which featured a humbucking transformer (Neumann designation ‘BV11’) with 4dB higher output and a noticeably improved noise floor that also could be switched between 50 and 200 ohms output impedances.

Additional 'b' features:

* fixed low cut (5 megΩ negative feedback) 

* AC701 current draw increased from .45mA to .73mA 

* high end cut shunt cap increased from 150pf to 600pf, resulting in larger high frequency roll-off, to comply with broadcast regulations 

* a circuit-mounted 'cardioid only' switch

* increased global feedback (after 12-1958)

The audibly biggest change to the M49 would be new Mylar® (Polyester) K49 capsule. Its overall dimensions, hole patterns and material composition were still largely based on those of the M7, but, because of minor deviation in diaphragm size, film composition and reduced diaphragm thickness, the new capsule sounded quite a bit different and promised little to no deterioration in performance through time.   

A few additional circuit modifications were introduced: selectable ultra-low-end cut (through wire switch), a contact-switch for cardioid-only operation, plus hardware and wiring changes. 

This was also the first M49 series available with a smaller, RF-tight, seven-pin broadcast Tuchel connector, instead of the larger, eight-pin bayonet-type. These connectors were mated to a new, Dörfler, Austria-made microphone cable type which was largely immune to radio frequency interference, due to its double Reussen (corkscrew) layers of plain copper wire surrounding the audio conductors resulting in a 100% shield coverage. The broadcast version of this M49 version attained the prefix ‘2’.  The new M249b were otherwise identical in build and performance to M49b of the same period which continued to be shipped to Neumann’s non-institutional customers at home and abroad-some with a Telefunken logo.

In late 1961. When the "b" serial number plates ran out, subsequent M49 plates were printed with the ‘c’ suffix (around late 1963.) Fairly soon after, all M49s were equipped with a printed circuit board to replace the earlier point-to-point wiring. 

The final, and audibly biggest, change happened in late 1961, when the tube biasing was converted from fixed to self-biasing of the cathode. All M49 and other AC701-equipped microphones from then on used this new biasing method which lowered the noise floor of the microphones, reducing stray hum and noise interference from outside sources as well. It also slightly altered the sound of any mic whose biasing was converted to “c”. Neumann mics used in broadcasting would be routinely converted to “c” circuitry during service in Berlin thereafter,  also receiving an embossed letter “c” on the i.d. plate. 

The M49 and its broadcast-connector version M249 continued to be built with identical components and circuitry, until around 1971, with some leftovers having been shipped through the late 1970s. This makes it the longest run of any of the Big Five - in production longer than any other vintage tube mic. Some original spare parts were still available from Neumann in Berlin until quite recently.

Mechanical and electrical revisions influenced the M49's sound through its generations. The greatest sonic impact in my opinion resulted after the switch-over from the M7 to the K47 capsule, followed by introduction of low-cut circuitry and increased negative feedback, and, still more subtle, by the various types of transformers Neumann used. 

Yet, the wonderfully subtle and effortless musicality of the most underrated mic among the Big Five can be enjoyed by any version of the M49.