GRAS - AllianTech
¼″ CCP Preamplifier Type 26CG, Infra-sound
Product Data
Typical Applications
■ Infra-sound measurements
■ Low-level measurements
■ General-purpose preamplifier
■ Use with ½″ Free-field Microphone,
Low-frequency Type 40AZ
Special Properties
■ Wide Frequency Range
■ Low Cut-off Frequency
■ Low Noise Level
Description
The G.R.A.S. ¼″ CCP Preamplifier Type 26CG is a
small robust unit optimised for acoustic measurements using condenser microphones. It has a very
low inherent noise level, a wide dynamic range,
and a wide frequency response from below 1 Hz to
above 200 kHz.
Type 26CG can easily be connected to any IEPE
input or to a G.R.A.S. Power Supply Type 12AQ or
Type 12AL.
The Type 26CG is delivered with a built-in TEDS **
chip (vers. 0.9) and can be programmed as a combined unit with a microphone fitted. It can be used
with all G.R.A.S. prepolarized microphones.
Type 26CG, Vers. 25 June .2009
Design
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
G. R . A . S.
SOUND & VIBRATION
Fig. 1 ¼″ Preamplifier Type 26CG
current of 4 mA. This leads to a maximum output
voltage of 8 Vpeak, the dynamic range thereby exceeding 126 dB.
Noise
The electrical circuit in Type 26CG preamplifier is
built on a ceramic substrate using selected lownoise 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
(Type 40AZ’s) thermal noise.
Frequency Response
The low-frequency cut-off of the Type 26CG preamplifier is mainly determined by the input impedance
of the preamplifier and the capacitance of the microphone capsule (see Fig. 2). The capacities 20 pF,
6.5 pF and 3 pF equal the typical capacitances of
½″, ¼″ and ⅛″ microphone capsules 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 (see Fig. 3).
Type 26CG is typically used with Type 40AZ, lowfrequency microphone capsule to reach a -3-dB cutoff frequency around 0.25 Hz.
Connectors and Adapter
Preamplifier Type 26CG (Fig. 1) is provided with a 3m lightweight cable terminating in a BNC plug. The
amplifier is connected to the cable via a Microdot
connector. The cable is only 2.0 mm in diameter and
withstands temperatures from - 40 oC to +150 oC. An
adaptor (GR0010) for G.R.A.S. ½″ microphones is
included.
*) Constant Current Power, equal to IEPE
**) Transducer Electronic Data Sheet - as specified by
IEEE-1451.4
Skovlytoften 33,
2840 Holte, Denmark
www.gras.dk gras@gras.dk
¼″ CCP Preamplifier Type 26CG, Infra-sound
Specifications
CCP preamplifier dependence of load and output level
5
5,00
0,00
-5,00
-10,00
20pF
-15,00
6.5pF
-20,00
3pF
-25,00
3p
F
-15
10,00
10,00
5,00
0,00
-5,00
-10,00
-15,00
0n
0n
1n
4.7n
1n
4.7n
10n
10n
47n
100n
47n
100n
-20,00
-25,00
-30,00
100
-20
Outpout level in dB ref 1V
Outpout level in dB ref 1V
pF
20
pF
-10
6.5
dB
-5
15,00
15,00
0
CCP preamplifier dependence of load and output level
1000
10000
Frequency in Hz
-30,00 100000
100
1000
10000
100000
Frequency in Hz
-25
0.1
1.0
10.0
100.0
1000.0
Hz
Fig. 2 Typical low-frequency response of Type 26CG
for ½″ (20 pF), ¼″ (6.5 pF) and ⅛″ (3 pF)
microphones
Technical Data
Frequency response (18pF/small signal):
1 Hz - 200 kHz
± 0.2 dB
Slew rate:
20 V/µs
Input impedance:
40 GΩ, 0.4 pF
Output impedance (Cs = 20 pF, f = 1000Hz):
Typical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Ω
Noise (measured with 20 pF ½″ dummy mic.):
A-weighted: . . . . . . . . . . . . . . . . . . . . ≤ 2.3 µ V rms
(typically 1.5 µ V rms)
Linear (20 Hz - 20 kHz): . . . . . . . . . . . . ≤ 6 µ V rms
(typically 3.2 µ V rms)
Gain:
Typical: . . . . . . . . . . . . . . . . . . . . . . . . . . - 0.25 dB
Power supply:
2 m A to 20 m A (typically 4 m A)
DC Output level:
12 V
Maximum signal-output voltage (peak):
8V
corresponding to 138 dB SPL for
microphone sensitivity of 50 mV/Pa
Temperature:
Operation: . . . . . . . . . . . . . . . . . . -30 oC to + 70 oC
Storage:. . . . . . . . . . . . . . . . . . . . - 40 oC to + 85 oC
Relative humidity:
Operation: . . . . . . . . . . . . . . . . . . . . . . . 0 to 95 %
Storage:. . . . . . . . . . . . . . . . . . . . . . . . . 0 to 95 %
Dimensions:
Diameter:. . . . . . . . . . . . . . . . . . . . . 6.35 mm (¼″)
Length: . . . . . . . . . . . . . . . . . . . . . . .43 mm (1.7″)
Weight (without cable): . . . . . . . . . . . 6 g (0.2 oz)
Weight (with cable + Microdot conn.): 50 g (1.76 oz)
Connector type:
Microdot (UNF 10-32)
Supply current: 4 mA for all measurements
Cable capacity properties: RG58: 100 pF/m, RG59: 50 pF/m
Fig. 3 Frequency response for three output levels.
At each output level the frequency response is
shown for the above-stated cable capacities.
Accessories
Included
GR0010:
¼″ to ½″ adapter for use with
G.R.A.S. ½″ microphones
AA0018:
Extension cable, Microdot
(UNF 10-32) to BNC, 3 metres
Optional
RA0001:
Right-angled (90º) Adapter for
½″ microphone and ¼″ preamplifier
RA0003:
Adapter for ½″ microphone and
¼″ preamplifier
RA0006:
Angled (90º) Adapter ¼″ to ¼″
AA0060:
Extension cable, Microdot
(UNF 10-32) to BNC,1 meter
AA0061:
Extension cable, Microdot
(UNF 10-32) to BNC, 5 metres
AA0062:
Extension cable, Microdot
(UNF 10-32) to BNC, 10 metres
AE1038
Microdot (UNF 10-32) Adapter
(Female-Female)
AA0013:
Tripod adapter for ¼″ preamplifier
RA0096:
Tripod adapter for ¼″ preamplifier
with angular adjustment
G.R.A.S. Sound & Vibration reserves the right to change specifications and accessories without notice.
G. R . A . S.
SOUND & VIBRATION
Skovlytoften 33,
2840 Holte, Denmark
www.gras.dk gras@gras.dk
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