GRAS 26AR 1/4″ Standard Preamplifier with Integrated Mini-connector

Typical applications and use

• For use in confined spaces
• High frequency measurements
• High pressure measurements
• Sound intensity measurements
• Near-field measurements
• Anechoic boxes
• Hearing-aid measurements

Special Properties

• Wide frequency range
• Low noise level
• Very small dimensions
• 4-pin LEMO 00 connnector

Design

All GRAS microphone preamplifiers are based on a small ceramic thick-film substrate with avery 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

GRAS 26AR can handle both single and dual-sided power supplies. The supply can vary between 28 VDC and 120 VDC single-sided or ±14VDC and ±60 VDC dual-sided. When using the high supply voltage (120VDCor ±60VDC), the dynamic range exceeds140 dB.

Noise

The electrical circuit in GRAS 26AR 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 GRAS 26AR 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 GRAS 26AR 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 100pF/m (30pF/foot).

Connector

GRAS 26AR is to be connected with a 3m light-weight cable (AA0057). Its 4-pin LEMO plug connects to the preamplifier and its 7-pin LEMO to a power module. The cable is only 2.5 mm in diameter and will withstand temperatures from -40 ^oC to +150 ^oC. An adapter GR0010 for GRAS 1/2″ microphones is included.

Ext. view of 4-pin LEMO plug 00 male and 7-pin LEMO plug 1B male (ext. view)