GRAS 26TC 1/4'' Preamplifier with 3 m integrated Cable
Freq range: 2 Hz - 200 kHz
Noise: 1.8 µV
Gain: -0.25 dB
Special feature: General purpose
The GRAS 26TC 1/4" Preamplifier is a small robust unit optimised for acoustic measurements using condenser microphones. It has a very low inherent noise level, a wide dynamic range and a frequency response from below 2 Hz to above 200 kHz.
Technology
Design
All GRAS microphone preamplifiers are based on a small ceramic thick-film substrate with a very high input impedance. The ceramic substrate is shielded by a guard ring to minimise the influence of stray capacitance and microphonic interference. The casing is made of stainless steel for maximum strength and durability. The small dimensions of this preamplifier ensure reliable operation under humid conditions owing to the heat generated by internal power dissipation.
The 26TC is delivered with a built-in TEDS chip and can be programmed as a single unit with a microphone fitted. An adaptor (GRAS GR0010) for GRAS 1/2" microphone cartridges is included.
Dynamic range
GRAS 26TC can handle both single and dual-sided power supplies. The supply can vary between 28 VDC and 120 VDC single-sided or ±14 VDC and ±60 VDC dual-sided. When using the high supply voltage (120 VDC or ±60 VDC), the dynamic range exceeds 140 dB.
Noise
The electrical circuit in GRAS 26TC is built on a ceramic substrate using selected low-noise components to gain very low self-noise. The electrical self-noise is so low that system noise is mainly determined by the microphone capsule’s thermal noise.
Frequency Response
The low-frequency cut-off of the GRAS 26TC preamplifier is mainly determined by the input impedance of the preamplifier and the capacitance of the microphone cartridge (see the graph in the Specifications). The capacities 20 pF,6.5 pF and 3 pF equal the typical capacitances of 1/2", 1/4"" and 1/8" microphone cartridges respectively. The high-frequency cut-off is determined by the preamplifier’s ability to drive capacitive loads (slew rate), caused by the cable. For large-signals, the effects of these parameters must be accounted for when measurements are performed. A graph in the Specifications shows the large-signal response for GRAS 26TC for various capacitive loads corresponding to different cable lengths. The output level is in decibels relative to 1 Volt. Typical capacitance for the cable is 100pF/m (30pF/foot).
Connector
Preamplifier Type 26TC is provided with a 3-m lightweight cable terminating in a 7-pin LEMO series 1B plug. The cable is only 2.5 mm in diameter and will withstand temperatures from -40°C to +150 °C. An adaptor (GR0010) for GRAS 1/2" microphones is included.
7-pin LEMO plug 1B male (ext. view)
Typical applications and use
General-purpose preamplifier
High-frequency measurements
High-pressure measurements
Specifications
Dimensions
Ordering info
| GRAS AA0008 | 3 m LEMO 7-pin - LEMO 7-pin Cable |
| GRAS AL0029 | 1/4" Microphone Holder, POM |
| GRAS AL0013 | 1/4" Microphone Holder, Stainless Steel |
| GRAS AL0005 | Swivel head |
| GRAS AL0006 | Tripod |
| GRAS RA0063 | Adapter for 1/8" microphone and 1/4" preamplifier |
| GRAS RA0006 | Right-angled (90º) Adapter for 1/4" Microphone and 1/4" Preamplifier |
| GRAS RA0002 | Right-angled adjustable adapter for 1/2'' mic/ 1/4'' preamp. |
| GRAS RA0080 | 6pF Preamplifier-input adapter for 1/4" microphones |
| GRAS 12AA | 2-Channel Power Module with gain, filters and SysCheck generator |
| GRAS 12AQ | 2-Channel Universal Power Module with signal conditioning and PC interface |
| GRAS 12BC, 12BF and 12BD | LEMO Power Modules with TEDS Support |
