GRAS 26AC-1 1/4" Standard Preamplifier with Integrated Miniconnector
Freq range: 2.5 Hz - 200 kHz
Noise: 1.8 µV
Gain: -0.29 dB
Special feature: General purpose
The GRAS 26AC-1 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 minimize the influence of stray capacitance and microphonic interference. The casing is made of stainless steel for maximum strength and durability. This preamplifier ensures reliable operation even under humid conditions owing to the heat generated by internal power dissipation.
The 26AC-1 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 26AC-1 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 26AC-1 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 cartridge’s thermal noise.
Frequency response
The low-frequency cut-off of the GRAS 26AC-1 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 26AC-1 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
The GRAS 26AC-1 1/4" Preamplifier is provided with a 5-pin LEMO series integrated connector. Cables for conversion to standard 7-pin LEMO series 1B plug are available.
5-pin LEMO plug 00 male (ext. view)
Typical applications and use
General-purpose preamplifier
High-frequency measurements
High-pressure measurements
Specifications
Conditions: 23 °C Ambient temperature, ±60V/+120V power supply, 18 pF dummy microphone, 3 m output cable.
Typical frequency response for 1/2" (20 pF), 1/4" (6.5 pF) and 1/8" (3 pF) microphones
Typical max RMS output signal with 120 V and 30 V supply
GRAS Sound & Vibration reserves the right to change specifications and accessories without notice.
Dimensions
Ordering info
Included items
| GRAS GR0010 |
Adapter for 1/4" preamplifier and 1/2" microphone |
Optional items
| GRAS AA0091 |
3 m LEMO 5-pin - LEMO 7-pin Cable |
| GRAS AL0029 |
1/4" Microphone Holder, POM |
| GRAS AL0013 |
1/4" Microphone Holder, Stainless Steel |
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Swivel head |
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| GRAS AL0006 |
Tripod |
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Adapter for 1/8" microphone and 1/4" preamplifier |
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Right-angled (90º) Adapter for 1/4" Microphone and 1/4" Preamplifier |
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6pF Preamplifier-input adapter for 1/4" microphones |
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2-Channel Power Module with gain, filters and SysCheck generator |
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2-Channel Universal Power Module with signal conditioning and PC interface |
GRAS Sound & Vibration reserves the right to change specifications and accessories without notice.
