Cardioid Condenser Microphone
The AM51 was one of the first microphones released by GT Electronics, the analog product division created when Alesis acquired Groove Tubes. It is a fixed Cardioid FET condenser with switchable pad and filter and transformer output, and was billed as an all-purpose studio condenser.
The capsule is the same as was found in all the Groove Tubes large-diaphragm models, a ~33mm K67 derivative with a resonator disk attached to the active diaphragm to smooth out the high-frequency response.
The circuit is a Class A JFET design with an output transformer. It has high gain (32mV/Pa) and relatively high self-noise (22dBA); these characteristics were common to all Groove Tubes and Alesis/GT condensers.
Switches on the mic independently enable a pad (-10dB) and high-pass filter (12dB/octave at 75Hz).
The AM51 circuit is extremely similar to the GT55, ST55, and M-Audio Nova circuits that we’ve seen.
Permalink: Alesis AM51
The mic was released in 1999.
|Pickup Patterns||Pads & Filters|
(32 mV/Pa; 20 - 18,000 Hz)
| Diaphragm diameter: 25mm
Capsule diameter: 32mm
Diaphragm gauge: 3 microns
|200 Ohms (Low)||Self-noise: 22.0 dB(A)|
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