G.R.A.S. 26CG 1/4" CCP Preamplifier with Microdot Connector, Low Frequency

Freq range: 1 Hz - 200 kHz
Noise: 1.8 µV
Gain: -0.35 dB
Special feature: For low-frequency applications

Typical Applications

  • Infra-sound measurements
  • Low-level measurements
  • General-purpose preamplifier
  • Use with 40AZ ½″ Free-field Microphone, Low-frequency

Special Properties

  • Wide Frequency Range
  • Low Cut-off Frequency
  • Low Noise Level

G.R.A.S. 26CG can easily be connected to any IEPE input or to a G.R.A.S. 12AQ or 12AL Power Supply.

The 26CG is delivered with a built-in TEDS chip and can be programmed as a combined unit with a microphone fitted. It can be used with all G.R.A.S. prepolarized microphones.


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

Dynamic Range

The lower limit of the dynamic range is determined by the noise floor. The upper limit of the dymamic range is determined by the power module: Type 12AQ, sourced at 28 V DC, supplies a constant current of 4 mA. This leads to a maximum output voltage of 8 Vpeak, the dynamic range thereby exceeding 126 dB.


The electrical circuit in the G.R.A.S. 26CG preamplifier 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 (G.R.A.S. 40AZ’s) thermal noise.

Frequency Response

The low-frequency cut-off of the 26CG preamplifier is mainly determined by the input impedance of the preamplifier and the capacitance of the microphone cartridge. The capacities 20 pF,6.5 pF and 3 pF equal the typical capacitances of ½″, ¼″ and ⅛″ 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.

G.R.A.S. 26CG is typically used with G.R.A.S. 40AZ, low frequency microphone cartridge to reach a -3-dB cut-off frequency around 0.25 Hz.

Connectors and Adapters

26CG Preamplifier is provided with a Microdot connector. An adaptor (GR0010) for G.R.A.S. 1/2" microphones is included.

Frequency range (±0.2 dB) with 18 pF microphone dummy Hz 1 to 200 k
Slew rate V/µs 20
Input impedance GΩ // pF 40 // 0.4
Output impedance Ω < 50
Output Voltage Swing, min. @ 24-28 V CCP voltage supply Vp 8
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 -0.35
Power supply (Constant Current Power) mA 2 to 20 (typ. 4)
DC bias voltage, typ. V 12
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) 769 v. 0.9
Connector type Microdot 10/32
CE/RoHS compliant/WEEE registered Yes / Yes, Yes
Weight g / oz 6.0 / 0.21

Conditions: 23 °C Ambient temperature, 4 mA / 24 V open loop CCP voltage, 18 pF dummy microphone & 3 m coax-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. AA0070

3 m Microdot - BNC Cable

G.R.A.S. AA0073-CL

Customized Length Microdot - BNC Cable

G.R.A.S. AA0087-CL

Customized Length Microdot - Microdot 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. 12AL

1-Channel CCP Power Module with A-weighting filter

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.