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Mods for the GT55

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Groove Tubes GT55

Pricing & Availability

  • MSRP: $599
  • Discontinued


Reviews & News

GT55 Documentation

CardioidGroove Tubes GT55

Cardioid Condenser Microphone

The GT55 was an early FET condenser from Groove Tubes, replaced in the lineup in early 2006 by the GT50, which appears to have been identical save for the exterior metalwork.

Groove Tubes GT55 PCBThe GT55, like all the company’s LDCs, uses a 3-micron, 33mm K67-type capsule with a “disk resonator” attached to the center termination screw to increase high-frequency response. In the GT55, this capsule has a non-metallized rear diaphragm.

The mic has very high sensitivity of 32mV/Pa, making the onboard -10dB pad likely very useful for capturing medium- to loud sources. A second switch on the mic body enables a high-pass filter.

The GT55 has a fixed Cardioid pickup pattern. The capsule bias voltage on a sample mic was measured to be 38VDC.

The grille is made of 2-layer metal mesh. In the sample we’ve seen, the inner layer is loose, not soldered to the chassis.

It was introduced sometime around 2001-2002 at $599. The MSRP dipped as low as $399 over the mic’s ~4-year lifetime, when distributed by M-Audio.

Although the cutsheet claims a max diameter of 2.5'', we suspect this was a typo; the body diameter is more likely ~46mm (1.8 inches).

ProAudio Review, 2003

This 3-micron evaporated gold diaphragm with Disk Resonator technology provides amazing sensitivity that delivers a sparkling, transparent sound across the full frequency spectrum… Large-diaphragm microphones often get bogged down resonating at low frequencies, preventing them from efficiently reproducing frequencies above 14–15 kHz. Groove Tubes’ Disk Resonator interacts at high frequencies with part of the diaphragm, extending the range of the capsule well beyond 20 kHz.

The Sterling Audio ST55 FET is likely very similar to the GT55; it boasts identical specifications, and although the frequency graph is subtly different, this could be explained by differences in test procedures rather than by component differences in the microphone.

Permalink: Groove Tubes GT55


Pickup Patterns Pads & Filters
Cardioid (32 mV/Pa; 20 - 18,000 Hz)
  • Pad: -10dB (Via Switch)
  • Filter: HPF: -12dB/octave @ 75Hz (Via Switch)
Capsule Dimensions Impedance SPL/Noise
Diaphragm diameter: 25mm
Capsule diameter: 33mm
Diaphragm gauge: 3 microns
200 Ohms (Low) Max SPL: 144 dB
Self-noise: 22.0 dB(A)
Weight Length Max Diameter Interface(s)
680g (23.99oz) n/a n/a
  • 3-pin XLR male (1)
Power Specifications
  • Requires phantom power
  • Phantom voltage: 48v

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