GRAS 26CG 1/4″ CCP Preamplifier with Microdot Connector, Low Frequency

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

GRAS 26CG can easily be connected to any IEPE input or to a GRAS 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 GRAS prepolarized microphones.

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 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 V_peak, the dynamic range thereby exceeding 126 dB.

Noise

The electrical circuit in the GRAS 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 (GRAS 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.

GRAS 26CG is typically used with GRAS 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 GRAS 1/2″ microphones is included.