GRAS 26AB 1/4''-1/2'' Universal Preamplifier with Integrated Connector

Freq range: 2.5 Hz - 200 kHz
Noise: 1.8 µV Gain: -0.29 dB
Special feature: For both 1/2" and 1/4" microphone cartridges

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 these preamplifiers ensure reliable operation under humid conditions owing to the heat generated by internal power dissipation.

These preamplifiers are compatible with ½″ microphones as defined in international standard IEC1094 Measurement Microphones, Part 4: Specifications for working standard microphones. The mounting thread (11.7 mm - 60 UNS-2) is compatible with other available makes of similar microphone preamplifiers.

Dynamic Range

GRAS 26AB can handle both single and dual-sided power supplies. The supply can vary between 28 VDC and 120 VDC single-sided or ±14VDC and ±60 VDC dual-sided. When using the high supply voltage (120VDC or ±60VDC), the dynamic range exceeds 140 dB.

Noise

The electrical circuit in GRAS 26AB 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 26AB preamplifieris mainly determined by the input impedance of the preamplifier and the capacitance of the microphone capsule. The capacities 20 pF,6.5 pF and 3 pF equal the typical capacitances of 1/2", 1/4" and 1/8" microphone capsules respectively.

The high-frequency cut-off is determined by the preamplifier’s ability to drive capacitive loads (slewrate), caused by the cable. For large-signals, the effects of these parameters must be accounted for when measurements are performed. Fig. 4 shows the large-signal response for GRAS 26AB for various capacitive loads corresponding to different cablelengths. The output level is in decibels relative to1 Volt. Typical capacitance for the cable is 100pF/m(30pF/foot).

Connector

Preamplifier GRAS 26AB is provided with an integrated 7-pin LEMO connector. For use with GRAS 1/2" microphones, 1/4"-to-1/2" Adapter AF0008 is supplied. AF0008 is an inline barrel adapter ensuring minimum influence on the sound field.

7-pin LEMO plug 1B male (ext. view)

Specifications

Frequency range (±0.2 dB) with 18 pF microphone dummy
Hz
2.5 to 200 k
Slew rate
V/µs
20
Input impedance
GΩ // pF
20 // 0.4
Output impedance
Ω
75
Output Voltage Swing, max. @ ±14V/+28V power supply
Vp
12
Output Voltage Swing, max. @ ±60V/+120V power supply
Vp
50
Noise (A-Weighted) max.
µV
2.5
Noise (A-Weighted) typ.
µV
1.8
Noise (Linear 20 Hz – 20 kHz) max.
µV
6
Noise (Linear 20 Hz – 20 kHz) typ.
µV
3.5
High-pass filter @3dB cut-off
Hz
TBD
Gain
dB
-0.29
Power supply, single
V
28 to 120
Power supply, balanced
V
±14 to ±60
DC-offset, min., single suppy
V
0.5 x Vs - 1
DC-offset, max., single suppy
V
0.5 x Vs + 4
Temperature range, operation
°C / °F
-30 to 70 / -22 to 158
Temperature range, storage
°C / °F
-40 to 85 / -40 to 185
Humidity range non condensing
% RH
0 to 95
Connector type
7-pin LEMO (FGG.1B.307)
CE/RoHS compliant/WEEE registered
Yes / Yes, Yes
Weight
g / oz
22.0 / 0.78
Specification Conditions

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

AF0008

Adapter for 1/4" preamplifier and 1/2" microphone

 

Optional items

GRAS AA0008

3 m LEMO 7-pin - LEMO 7-pin Cable

GRAS AA0020-CL

Customized Length LEMO 7-pin - LEMO 7-pin Cable

GRAS AL0029

1/4" Microphone Holder, POM
(for use when AF0008 is not mounted)

GRAS AL0013

1/4" Microphone Holder, Stainless Steel
(for use when AF0008 is not mounted)

GRAS AL0008

1/2" Microphone Holder, POM
(for use when AF0008 is mounted)

GRAS AL0012

1/2" Microphone Holder, Stainless Steel
(for use when AF0008 is mounted)

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 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 Sound & Vibration reserves the right to change specifications and accessories without notice.

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