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9 polar patternsBlackspade Acoustics UM17

Multi-Pattern Tube Condenser Microphone

The UM17 is a large-diaphragm multipattern tube condenser, designed and built in the US by AMI.

Although prototyped as a modified version of the Alctron HST-11A, the shipping version of the microphone uses no Alctron parts. The body, metalwork, and capsule are built to Blackspade/AMI specifications, and have little in common with the T11A/Apex 460.

The UM17 can be thought of as a third-generation version of a mic mod developed by Oliver Archut in the early 1990s — in which the combination of a Chinese capsule and metalwork with an EF732 tube, a new amplifier circuit design and transformer, led to an affordable yet high-quality microphone.

A revised version of this design saw commercial release as the Telefunken Elektroakustik RFT AK47.

The latest incarnation swaps the AK47’s BV47 transformer for a new design, dubbed the BV8LP — a low-profile version of the U47’s BV8 transformer. The new transformer uses all-nickel lamination, unlike the BV47’s mix of nickel and iron.


[T]he BV8LP [is] a low profile version of the historic BV8 [designed] to fit in the mic body which is smaller than a U47. Using all nickel lamination, the BV8LP is a higher quality transformer that produces a more detailed output than the BV47, with improved low-frequency response and clarity to optimize the EF732 tube.

During prototyping, the UM17 used a capsule described as an “Alctron K47” — a dual-backplate, center-terminated design that originated in China.

The Alctron capsule has been dropped in favor of a capsule called the Blackspade K17 — a 32mm, single-backplate hybrid design based on the Neumann K47 and Gefell M7. It is a center-terminated capsule with dual 6-micron diaphragms. These capsules are imported from overseas, tuned and tested in the US by AMI.

See also the UM17R, which swaps the K17 capsule for a Thiersch M7.

AMI supplies a NOS EF732/5840 tube, branded Telefunken or Syvlania. The tube is warrantied for 6 months.

The power supply is sourced in China, but rebuilt and optimized in the US for the EF732 tube.

The amplifier circuit developed for the AK47 has been revised to best match the capsule and transformer in the new microphone. The circuit was designed by Oliver Archut.

The UM17 is assembled and tested in Gaylord, KS, using a mix of locally-supplied and imported parts. It ships with its power supply and cable, an elastic shockmount, a “wind sock” mic cover, and a flight case.

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The mic was released in 2010.


Pickup Patterns Pads & Filters
Omnidirectional (14 mV/Pa; 20 - 20,000 Hz)
Cardioid (14 mV/Pa; 20 - 20,000 Hz)
Bidirectional (14 mV/Pa; 20 - 20,000 Hz)
Capsule Dimensions Impedance SPL/Noise
Diaphragm diameter: 25mm
Capsule diameter: 32mm
Diaphragm gauge: 6 microns
200 Ohms (Low) Max SPL: 132 dB
Self-noise: 17.0 dB(A)
Weight Length Max Diameter Interface(s)
775g (27.34oz) 245mm (9.65'') 44mm (1.73'')
  • 3-pin XLR male (1)
Power Specifications
  • Includes tube power supply

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