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BidirectionalAEA A840

Bidirectional Ribbon Microphone

The A840 has been renamed “R84A,” to reflect that it is an R84 with active electronics. The rest of this profile is believed to still be accurate for the R84A.

The A840 is a large-geometry ribbon microphone with an onboard JFET amplifier circuit. It is essentially an “active” version of the company’s R84 passive ribbon.

The amplifier circuit is transformerless. It was designed by Fred Forssell for AEA.

The mic uses the same ribbon element as the company’s R84 and A440: 1.8µ aluminum, measuring 4.7mm x 59.7mm. The ribbon is tuned to 16.5Hz.

The ribbon motor itself is the same as found in the R84; both are significantly smaller than the 5lb (2.2kg) motor assemblies in the RCA-style mics (the A440 and R44 series).

The aluminum ribbon is centered in the magnetic gap, yet the mic produces a subtly different frequency response from the rear. The response change is intended to provide users with two “colors” from a single microphone. The tonality change is caused by the use of different wind/blast protection on the rear side of the microphone. According to Wes Dooley, the rear side of the mic can better withstand plosives.

At 17.5 dBA, the mic’s self-noise is higher than many premium large-diaphragm condensers, as well as the A440 (6dBA). (The low noise level of the A440 is due primarily to that mic’s giant ribbon motor.)

Although Scott Dorsey’s review in Recording Magazine suggests that the A840’s step-up transformer is from Lundahl, the Forssell Technologies website states that the transformer was designed by Fred Forssell.

The A840 is available in four varieties:

  • A840-TW - non-reflective exterior
  • A840-M - hand-tuned, matched stereo pair
  • A840-C - Custom cable length
  • A840-U - Custom laser-engraved trim band

Most of these add-on options carry a $100 upcharge.

The mic ships with a 3m Accusound audio cable (permanently attached to the microphone), and AEA’s “Vertical Mic Storage Case.”


AEA “BIG RIBBON™” mics use a long rectangular diaphragm clamped only at the ends and tensioned lightly with a fundamental resonance below 20 Hz. Less than 80 millionths of an inch thick, our ultra low-mass transducer has extended bass, excellent transient response and few resonances. It’s one of the most sensitive and accurate transducers possible.

Scott Dorsey, Recording Magazine, 2010

The overall sound of the A840 is like that of a classic ribbon mic, but it’s definitely more extended and less ragged on top. The more extended and much less colored top end makes the A840 a more versatile mic.

Permalink: AEA A840

The mic was released in 2009.


Pickup Patterns Pads & Filters
Bidirectional (6.3 mV/Pa; 20 - 5,000 Hz)
Ribbon Construction Impedance SPL/Noise
Length: 59.7mm
Width: 4.7mm
Gauge: 1.8 microns
92 Ohms (Low) Max SPL: 141 dB
Self-noise: 17.5 dB(A)
Weight Length Max Diameter Interface(s)
850g (29.98oz) 295mm (11.61'') 64mm (2.52'')
  • 3-pin XLR male (1)
Power Specifications

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