Bộ tiền khuếch đại GRAS 26AS 1/4" tiêu chuẩn với cáp tích hợp 3 m, rất ngắn.

The GRAS ¼" Preamplifier Type 26AS is a small robust unit short enough for use in confined spaces, e.g., for binaural measurements with the KEMAR Manikin (GRAS 45BB or GRAS 45BC) or GRAS 45CA Hearing-protector Test Fixture. It has a very low inherent-noise level, a wide dynamic range, and a frequency response from below 2 Hz to above 200 kHz.

Technology

Typical applications and use

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

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

Dynamic Range

GRAS 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.

Noise

The electrical circuit in GRAS 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 GRAS 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).

Connector

The GRAS 26AS is provided with a 3 m lightweight cable terminating in a 7-pin LEMO series 1B plug. The cable is only 2.5 mm in diameter and will withstand temperatures from–40 °C to +150 °C. An adaptor GR0010 for GRAS 1/2" microphones is included.

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

Specifications

Parameter	Unit	Value
Frequency range (±0.2 dB) with 18 pF microphone dummy	Hz	2.5 to 80 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