G.R.A.S. 26AS 1/4" Standard Preamplifier with 3 m Integrated Cable, Very Short

Freq range: 2.5 Hz - 200 kHz
Noise: 4 µV
Gain: -0.29 dB
Special feature: For confined spaces

Typical applications and use

  • Confined spaces
  • High frequency measurements
  • High pressure measurements
  • Sound intensity measurements
  • Near-field measurements
  • Anechoic boxes
  • Hearing-aid measurements


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 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 ensures reliable operation under humid conditions owing to the heat generated by internal power dissipation.

Dynamic Range

G.R.A.S. 26AS 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 VDCor ±60 VDC), the dynamic range exceeds140 dB.


The electrical circuit in G.R.A.S. 26AS 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 G.R.A.S. 26AS preamplifier is mainly determined by the input impedance of the preamplifier and the capacitance of the microphone capsule. The capacities 20 pF,6.4 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 (slewrate), caused by the cable. For large-signals, the effects of these parameters must be accounted for when measurements are performed. The large-signal response for Type 26AS for various capacitive loads corresponding to different cable lengths is shown in the data sheet. The output level is in decibels relative to 1 Volt. Typical capacitance for the cable is 100 pF/m(30pF/foot).


The G.R.A.S. 26AS is provided with a 3 m light weight cable terminating in a 7-pin LEMO series 1B plug. The cable is only 2.5 mmin diameter and will withstand temperatures from–40 oC to +150 oC. An adaptor GR0010 for G.R.A.S. 1/2" microphones is included. The 26AS is also available as 26AS-CL with customized cable lengths up to 10 meters. Then specify the wanted cable length in cm.

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

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 10
Output Voltage Swing, max. @ ±60V/+120V power supply Vp 50
Noise (A-Weighted) max. µV 6
Noise (A-Weighted) typ. µV 4
Noise (Linear 20 Hz – 20 kHz) max. µV 10
Noise (Linear 20 Hz – 20 kHz) typ. µV 8
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 bias voltage, typ. V -1.5 to 5
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 TBD / TBD
Weight with cable and connector g / oz TBD / TBD

Conditions: 23 °C Ambient temperature, ±60V/+120V power supply, 18 pF dummy microphone, 3 m output cable.


Typical low-frequency response of Type 26AL for ½″ (20 pF), ¼″ (6.5 pF) and ⅛″ (3 pF) microphones




Typical max. rms output signal with 120 V and 30 V supply


G.R.A.S. Sound & Vibration reserves the right to change specifications and accessories without notice.

Included items


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


Optional items

G.R.A.S. AA0020-CL

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

G.R.A.S. AL0029

1/4" Microphone Holder, POM

G.R.A.S. AL0013

1/4" Microphone Holder, Stainless Steel

G.R.A.S. AL0005

Swivel head

G.R.A.S. AL0006


G.R.A.S. RA0063

Adapter for 1/8" microphone and 1/4" preamplifier

G.R.A.S. RA0006

Right-angled (90º) Adapter for 1/4" Microphone and 1/4" Preamplifier

G.R.A.S. RA0080

6pF Preamplifier-input adapter for 1/4" microphones

G.R.A.S. 12AA

2-Channel Power Module with gain, filters and SysCheck generator

G.R.A.S. 12AQ

2-Channel Universal Power Module with signal conditioning and PC interface

G.R.A.S. Sound & Vibration reserves the right to change specifications and accessories without notice.