copyright 1997 by Eddie Ciletti
Unlike Ed Colverís artful technique of capturing classic "transducers"
featured monthly in EQ MAgazine, this undercover edition chose the sensational
approach, using a hidden Hi-8 video camera to expose the secret life of
a classic mic. Welcome to Microphile Undressed. A mere student
of microphone technology, I am a very lucky enthusiast, especially when
an acquaintance brings two extremely mint condition Telefunken U-47s to
my shop for evaluation.
WHATíS HIS NAME?
At one time, Telefunken distributed microphones made by Georg Neumann
as well as those by AKG. Some were "customized" versions tweaked
to Telefunkenís specs, others were completely "stock." In case you
didnít know, the name is pronounced "noy-mahn," not "new-man," like that
guy on the Seinfeld show.
Needless to say, even my own normally skilled hands were a bit more
tremble-prone. Unlike Phillips head screws which securely mate with
their drivers, all of the U-47 screws required a flat bladed screwdriver
which was more likely than not to wander off the head. Since the
cases were literally perfect, I couldnít afford to make a single scratch.
TAKE TWO CAPSULES AND CALL MEÖ
Even though one mic seemed to be in working order, odds are the its
capsule would fail sooner than later. And so, being a symmetry freak, my
first thought was to have both capsules rebuilt. This, however, was
not an option until the day before this article went to press.
Mark McKenna at The Bearville Studios turned me on to Tracey Korby (412-937-1349)
who does capsule rebuilds ($600) as well as microphone repairs.
Neumann (860-434-5220) does sell replacement capsules for about $900,
but these are the more modern, mechanically clamped versions. I wanted
the mics to remain as close to the original as possible. Another
option is Stephen Paul Audio (818-905-9952) where a complete overhaul goes
for about $1600.
I eventually found a one-time alternate source for the M-7 capsule so
that, with parts and labor, the job was completed for about $900.
A steady hand is even more crucial when changing the capsule wires.
One slip and the capsule would be toast! These are not, in any way,
TUBE IN A CAN
Since these mics were rarely, if ever used, both VF-14 pentode vacuum
tubes were in great shape. And yes (for those in the know) each had an
"M" stamped on the case indicating the tube had been factory tested and
selected for low noise. A VF-14 is more rare than an honest politician.
(None of the former were made after WWII and none of the latter ever existed!)
Joe Leung at Gotham Service Labs (212-967-3120) tells me there are similar
pin-compatible tubes ó the EF-14 and the UF-14 ó which are somewhat more
available and less pricey (about $350). This approach requires no
mechanical modifications although a few circuit changes are necessary.
At one time, Neumann made a Nuvister "kit" which adapted a subminiature
tube to fit in the original socket. Nat Priest (212-343-0265) created
his own version of this vacuum tube alternative for under $200. Stephen
Paul Audio also has a more modern, nine-pin upgrade.
Any aged electronic device is likely to require some "maintenance"
even if never plugged in. This is especially true of electrolytic
capacitors. So far, however, no parts required changing but both
mics are under observation for signs of potential failure.
I did, however, increase the value of the polarizing and bias resistors
from 100 meg and 60 meg, respectively, to 160 meg ohms each. The
original values created a gradual low-frequency roll-off and, based on
a suggestion given by David Josephson, I made the changes while keeping
the original parts. Not only was David especially patient with my
numerous emails, he also suggested a great primer on Microphones by Dr.
Gerhart Bore. (the "e" should have an accent mark over it) This book
was distrubuted by Neumann, but may no longer be in print.
Itís not difficult to see why the U-47 remains one of the popular vocal
mics. Warm, but not murky, present but not irritating, you can easily
imagine itís impact on popular music back in the fifties. It certainly
contributed to the "High Fidelity" sound of that era!
PS Thanks also to Russ Hamm and Phil Kapp at G Prime (212-765-3415).