Neumann M 147 Tube
A transformerless tube condenser that borrowed the U 47's capsule and made a generation of engineers reach for their wallets.
Overview
The M 147 Tube is a side-address, vacuum-tube condenser microphone built around a dual-diaphragm capsule. Neumann fitted it with the K 47/49 pressure-gradient capsule used in the U 47 and the M 49. Few microphone makers can make a lineage claim like that. The capsule is the heart of a condenser mic, and this one is a genuine piece of Neumann history. The M 147 is that capsule recipe in a modern, affordable tube mic.
The pattern is fixed cardioid. The polar response becomes more directional as frequency rises, so the mic acts more like a supercardioid in the high-frequency range. That means a little more off-axis rejection up top and a touch more reach on the front. The capsule's frequency response is essentially flat into the upper midrange, then carries a boost of no more than 3 dB above 2 kHz. It's a gentle presence lift, not a spike.
The M 147 departs from its ancestors at the output stage. It uses a transformerless output circuit, which Neumann chose to keep self-noise to a minimum. The numbers back it up: a signal-to-noise ratio of 70 dB per CCIR 468-3, and a dynamic range for the mic amplifier of 102 dB for less than 0.5% THD (DIN/IEC 651). The frequency range runs 20 Hz to 20 kHz. Sensitivity at 1 kHz into 1 kohm is 20 millivolts/Pa, and rated impedance is 50 ohms. Maximum output voltage is 8 dBu, and the typical SPL for less than 0.5% THD is 114 dB. Those are clean, low-noise numbers for a tube microphone.
The tube is a subminiature triode, run for a gain of about 10 dB, and it doubles as an impedance converter. The microphone delivers a high output voltage, so it can drive cables up to about 300 meters long. To keep the tube's anode current and heater voltage optimal no matter how long the cable is, Neumann built a compensation circuit into the N 149 A power supply. A sensor monitors voltage through the length of the cable, and if it detects an unacceptable heater voltage the supply compensates for the difference. The N 149 A also uses a slow start-up to maximize tube life. The N 149 and N 149 V supplies used for the M 149 Tube can also power the M 147.
The physical package looks like the U 47's smaller sibling, with the classic Neumann nickel finish and a very similar body and head-grille shape in a more compact form. Neumann points out that although it looks like a vocal microphone, it's intended as a spot mic for just about any purpose, with vocal, string instruments, wind instruments, and piano all named. The mic ships with an aluminum case, cable, the SG 1 metal swivel stand adapter, the power supply, and a cable.
The reception was strong, and specific. EQ (March 1999, p.60) put the M 147 through sessions and reported the first use was on a Barbra [session]. The reviewer's habit was to power the tube mics up early and leave them plugged in so they'd be warmed for about an hour before recording. The magazine's own verdict, echoed in Neumann's advertising of the period, was that the mic brings warmth, presence, and detail to vocals that's hard to come by elsewhere. Working engineers said the same. Al Schmitt, quoted in EQ (March 1999), said he was thrilled with the mic and couldn't think of an instrument he wouldn't try it on, and he wished he had five or six. Myles Boisen recommended it for rock, rap, pop, jazz, and blues vocals, drum room and kick drum miking, tube and solid-state instrument amplifiers, nylon-string guitar, and low-volume or indistinct sources that need extra presence. He liked it so much he bought one. Monte McGuire called the character of its presence unique and not easily matched with an equalizer, and contrasted it with condenser mics that get brittle and edgy when pushed forward. One engineer, working with a finite budget, picked the M 147 over the alternatives on a vocal session. He summed it up as classic Neumann sound with tube electronics and the U 47 legacy at a price that wouldn't savage the bank account.
That last point is the pitch Neumann itself made. The M 147 is positioned as the way to get the classic tube sound without paying vintage-U 47 money. Neumann's advertising billed it as bringing the warmth and presence of the vintage greats within reach, and the independent reviews largely agreed the sound justified the claim. The ad copy is the manufacturer talking, while the magazine sessions are the actual verdict.
For collectors and working engineers alike, the M 147 occupies an interesting spot: it's a modern tube mic with a vintage capsule at its core, a transformerless circuit that keeps noise down, and a power supply designed to baby the tube. It isn't a reissue of the U 47 in any literal sense — the fixed cardioid pattern and the transformerless output are departures — but it carries the family DNA where it counts. The cross-compatibility with the M 149's power supplies makes it easy to slot into a Neumann tube locker, and the included swivel mount and case mean it arrives ready to work. The people who used it in the late '90s tended to keep using it, and the ones who bought one on a review's recommendation tended not to regret it.
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