

Groove Tubes GT-33
Detachable-Capsule Pencil Condenser Microphone
The GT-33 is a pencil condenser with interchangeable capsules and a transformer-coupled output. It was designed by Aspen Pittman, and introduced in 2001 at an MSRP of $599.
The mic has high sensitivity (26mV/Pa) and moderate self-noise (20dBA). Onboard switches enable a pad (-15dB, raising the max SPL to 150-155 depending on which version of the literature can be believed) and high-pass filter (-12dB/octave cutoff below 75Hz).
The mic shipped with a removable Cardioid capsule; Groove Tubes sold both Omni and Hypercardioid capsules separately. These capsules were also compatible with the GT-44 tube pencil mic.
The FET-based impedance-conversion circuitry is made with through-hole components. The output transformer is clearly visible on the board.
The Groove Tubes line was distributed by Midiman (later renamed M-Audio) beginning in 2001; in 2003, the GT33 FET had an MSRP of $399 for a single or $798 for “Certified Matched Pairs.”
Recording
I recently tried the M-Audio GT33 ($280), made by Groove Tubes, which is a medium-diaphragm solid-state mic. In my review I found the sound very close to that of a Shure SM81, but the GT33 has an omni capsule available as an accessory, [whereas] the SM81 doesn’t.
The Groove Tubes GT-33 is also known as: GT33 FET, GT33.
Specifications
Compatible Capsules | ||||||
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Pads & Filters | Impedance | SPL/Noise |
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200 Ohms (Low) | Max SPL: 155 dB Self-noise: 20.0 dB(A) |
Weight | Length | Max Diameter | Interface(s) |
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400g (14.11oz) | 190mm (7.48'') | 19mm (0.75'') |
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Power Specifications |
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