G.R.A.S. 26AC 1/4" Standard Preamplifier with 3 m Integrated Cable

Freq range: 2.5 Hz - 200 kHz
Noise: 1.8 µV
Gain: -0.29 dB
Special feature: General purpose

Design

All G.R.A.S. 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. The small dimensions of this preamplifier ensure reliable operation under humid conditions owing to the heat generated by internal power dissipation.

Dynamic Range

G.R.A.S. 26AC 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 G.R.A.S. 26AC is built on aceramic substrate using selected low-noise componentsto 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 G.R.A.S. 26AC preamplifier is mainly determined by the input impedanceof the preamplifi er and the capacitance of the microphone cartridge (see Fig. 3). 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. Fig. 4 shows the large-signal response for G.R.A.S. 26AC 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 G.R.A.S. 26AC 1/4" Preamplifier 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 oC to +150 oC. An adaptor (GR0010) for G.R.A.S. 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

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
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
DC-offset, balanced supply V -1 to 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 8.0 / 0.28
Weight with cable and connector g / oz 50.0 / 1.76
Conditions: 23 °C Ambient temperature, ±60V/+120V power supply, 18 pF dummy microphone, 3 m output cable.

Included

G.R.A.S. GR0010

1/4" to 1/2" adapter for use with G.R.A.S. 1/2" microphones

Optional

 G.R.A.S. 26AC-CL

 1/4" Preamplifier, Short version, customized cable length. Specify the length in cm (e.g. 26AC-CL0350 specifies a 350 cm (3.5 m) cable. Maximum cable length 10 meters

G.R.A.S. RA0001

Right-angled (90º) Adapter for½" microphone and ¼" preamplifier

G.R.A.S. RA0003

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

G.R.A.S. RA0006

Angled (90º) Adapter 1/4" to 1/4"

G.R.A.S. AA0008

Extension cable, 3 metres

G.R.A.S. AA0009

Extension cable, 10 metres

G.R.A.S. AA0012

Extension cable, 30 metres

G.R.A.S. AA0014

Extension cable, 100 metres

G.R.A.S. AA0020-CL

Extension cable, XX metres (customer-specified length)

G.R.A.S. AL0013

Tripod adapter for 1/4" preamplifier

G.R.A.S. RA0096

Tripod adapter for ¼" preamplifier with angular adjustment