G.R.A.S. 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


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. 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 (G.R.A.S. GR0010) for G.R.A.S. 1/2" microphone cartridges is included.

Dynamic Range

G.R.A.S. 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. 


The electrical circuit in G.R.A.S. 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 G.R.A.S. 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 G.R.A.S. 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).


The G.R.A.S. 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

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
TEDS UTID (IEEE 1451.4) 27 v. 1.0
Connector type 5-pin LEMO 00
CE/RoHS compliant/WEEE registered Yes / Yes, Yes
Weight g / oz 6.9 / 0.24

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

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. AA0091

3 m LEMO 5-pin - LEMO 7-pin Cable

G.R.A.S. AA0092-CL

Customized Length LEMO 5-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.