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Mods for the GT55
- Microphone Parts
The “T84-55” circuit kit from MicParts.com replaces the noisy GT55 circuit with a true vintage design (based on the Neumann KM84). This DIY audio kit uses a single-stage topology, and includes a vintage JFET (manually biased for maximum headroom), custom-wound and US made output transformer, and audiophile grade capacitors. - Microphone Parts
The “T84-55” circuit kit from MicParts.com replaces the noisy ST55 circuit with a true vintage design (based on the Neumann KM84). This DIY audio kit uses a single-stage topology, and includes a vintage JFET (manually biased for maximum headroom), custom-wound and US made output transformer, and audiophile grade capacitors. The modified’s mic’s output is higher, its self noise is lower, and the pad and filter switches are fully supported.
Pricing & Availability
- MSRP: $599
- Discontinued
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Reviews & News
GT55 Documentation
Groove 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.
The 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
Specifications
| Pickup Patterns | Pads & Filters |
|---|---|
|
Cardioid
(32 mV/Pa; 20 - 18,000 Hz) |
|
| 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 |
|
| Power Specifications |
|---|
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