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PRÉ-AMPLIFICADORES DE MICROFONE

Os pré-amplificadores de microfone da Brüel & Kjær são robustos e acusticamente otimizados para uma ampla gama de condições ambientais de funcionamento. A alta capacidade de corrente de saída de nossos pré-amplificadores é capaz de conduzir os cabos extremamente longos, sem degradação de sinal - mesmo com elevados níveis de pressão sonora presentes em altas frequências. Os designs do pré-amplificador CCLD Brüel & Kjær e do clássico pré-amplificador têm dimensões de 1/2 pol. e 1/4 pol., ajustando-se aos tamanhos dos cartuchos de microfone mais usados.

What is a Preamplifier
Microphone Preamplifier



TABLE OF CONTENTS

1. Preamplifiers for condenser microphones
 2. Classical Preamplifiers
3. CCLD Preamplifiers
4. Selecting a Preamplifier
5. Preamplifier Types

 

PREAMPLIFIERS FOR CONDENSER MICROPHONES

A condenser microphone must be combined with a preamplifier to provide impedance conversion, some filtering, and the capability to drive relatively long cables without significant signal degradation.

Our preamplifiers are designed in accordance with two principles, referred to as Classical Preamplifiers, and CCLD Preamplifiers. Each provide their own special set of features:

CLASSICAL PREAMPLIFIERS

The classical preamplifier has an easy to understand concept. It is basically a unity gain amplifier with extremely high input impedance and very low input capacitance. 

  • The supply voltage can be either ±15 V DC or a single 80 V DC.
  • The output signal has its own separate wire, as do the polarization and CIC voltage.
  • Pin 5 is often used for transmission of TEDS data (so called Class II TEDS).
  • Charge Injection Calibration (CIC) is performed by injecting a signal on pin 1 of the LEMO connector.

CCLD Preamplifiers

Despite its origin in the vibration transducer world, the Constant Current Line Drive (CCLD) principle is increasing in popularity in the area of sound and measurement applications. Different manufacturers market transducers using the CCLD principle under different names.

The benefit of CCLD is that the same wire is used for both the signal and the supply current. Using TEDS Class I even the TEDS data can be transmitted over that same wire (using a level controlled electronic switch as shown in the figure below). 

 

 

Classical vs. CCLD Preamplifier



 Classical CCLD
Output Voltage 55 Vp 7 Vp
Output Current 2 to 20 mA 3 to 20 mA
Noise <2 µV 4 µV
Distortion ≤ 80 dB ≤ 70 dB
Verification CIC/IVC No
IEEE 1451.4 Yes Yes
Cable Price Higher Lower
Connector LEMO BNC
Microphone Type Both Prepolarized only
Accelerometer Conditioning No Yes


SELECTING A MICROPHONE PREAMPLIFIER

Brüel & Kjær offer a large selection of robust and acoustically optimised preamplifiers that allow operation in a wide range of environmental conditions. The high output current capability of Brüel & Kjær preamplifiers allows the use of extremely long cables, even with high sound pressure levels present at high frequencies.

  • Preamplifiers are available in 1/2-inch and 1/4-inch dimensions, directly fittting with the most used cartridge sizes.
  • Adaptors are available for 1-inch and 1/8-inch microphone cartridges
  • The most popular classical 1/2-inch preamplifier is Type 2669. Available in several different versions.
  • Type 2669 combines a CCLD preamplifier and an A-weighting filter in a single unit. The preamplifier is easily distinguished due to the two engraved rings
  • When insert voltage calibration is required, Type 2673 is the obvious choice.
  • Type 2695, maybe due to its small size, (half the length of the extremely popular CCLD preamplifier Type 2671), is an often overlooked unit

A CCLD input can be connected to both microphones and vibration sensors (and many other sensors with CCLD output). Due to the working principle the signal is superimposed on a DC voltage. This DC bias voltage is typically around 12 V. Bias drift (over temperature or time) will reduce the dynamic range.

Due to the lower DC supply voltage (typically 20 – 28 V DC compliance voltage out of the front-end), there is some limitation in the upper limit for a CCLD solution. Another limitation of CCLD solution is that only prepolarized microphones can be used and that CIC is not available.

This, however, in many practical applications is happily accepted to reap the benefits of CCLD: Ease of use and cheap cables!
 

PREAMPLIFIER TYPES AND APPLICATIONS 

    ½-inch microphone preamplifier ½-inch microphone preamplifier ½-inch microphone preamplifier ¼-inch microphone preamplifier Type 1706
Type No.   2669-B 2669-L 2669-C 2670 1706
Diameter inch 1/2 1/2 1/2 1/4 1/2
Optimized   Acoustical* Acoustical Cylindrical Phase CCLD
Connector at Preamplifier   LEMO 0B, 7‐pin LEMO 0B, 7‐pin LEMO 1B, 7‐pin Fixed (2 m) BNC
Connector at Instrument/Cable   B&K, 7‐pin LEMO 1B, 7‐pin None LEMO 1B, 7‐pin N/A
Calibration Facility   CIC CIC CIC CIC None
Polarization Voltage Support   Yes Yes Yes Yes No
Supply Voltage V ±14 to ±60
or 28 to 120		 ±14 to ±60
or 28 to 120		 ±14 to ±60
or 28 to 120		 ±14 to ±60
or 28 to 120		 28
Max. Output Voltage (Peak) V 55
(5 below supply)		 55
(5 below supply)		 55
(5 below supply)		 55
(5 below supply)		 7
Max. Output Current (Peak) mA 20 20 20 20 19
Frequency Range Hz 3 to 200000
±0.5 dB
(15 pF)		 3 to 200000
±0.5 dB
(15 pF)		 3 to 200000
±0.5 dB
(15 pF)		 15 to 200000
±0.5 dB
(6.2 pF)		 20 to 50000
±2 dB (12 pF)
Attenuation dB <0.35 <0.35 <0.35 <0.4 <0.35
Noise A‐weighted, typical µV 1.9 1.9 1.9 4 4
Noise 22.4 Hz to 300 kHz, typical µV 8.2 8.2 8.2 14 15
Input Impedance GΩ || pF 15 || 0.3 15 || 0.3 15 || 0.3 15 || 0.25 6 || 0.5
TEDS UTID   1025 from
serial number
2221155		 1025 from
serial number
2221155		 1025 from
serial number
2221155		 1025 from
serial number
2248944		 1025 from
serial number
2264319
* Acoustical means a tapered preamplifier house. Other preamplifiers have cylindrical houses

 

    ¼-inch microphone preamplifier CCLD microphone preamplifier for 1/2-inch prepolarized microphones ½-inch microphone preamplifier with insert voltage facility ½-inch short CCLD preamplifier A-weighted Microphone Preamplifier - Type 2699
Type No.   2670-WB-1419 2671 2673 2695 2699
Diameter inch 1/4 1/2 1/2 1/2 1/2
Optimized   Airbag CCLD Calibration Short CCLD CCLD
Connector at Preamplifier   Fixed (2 m) cable BNC LEMO 0B, 7‐pin 10–32 UNF BNC
Connector at Instrument/Cable   LEMO 1B, 7‐pin N/A LEMO 1B, 7‐pin N/A N/A
Calibration Facility   None None IVC 10–32 UNF BNC
Polarization Voltage Support   Yes No Yes No No
Supply Voltage V ±14 to ±60
or 28 to 120		 28 ±14 to ±60
or 28 to 120		 28 28
Max. Output Voltage (Peak) V 55
(10 below supply)		 7 55
(10 V below supply)		 7 7
Max. Output Current (Peak) mA 20 19 19 19 18
Frequency Range Hz 1 to 100000
±1 dB (6.2 pF)		 20 to 50000
±2 dB (12 pF)		 3 to 200000
±0.5 dB (20 pF)		 20 to 50000
±2 dB (15 pF)		 A‐weighted to
IEC 61672 Class 1
Attenuation dB 11 <0.35 <0.05 <0.2 0, ±0.3 dB at
1 kHz
Noise A‐weighted, typical µV 4 4 1.8 4 8 Max., LIN
Noise 22.4 Hz to 300 kHz, typical µV 14 15 11 12 N/A
Input Impedance GΩ || pF 15 || 15 1.5 || 0.4 1 || 0.05 1.7 || 0.4 10
+20 to 40% || 0.5
TEDS UTID   1025 from serial
number 2264319		 1025 from serial
number 2264319		 No 1025 1025

WANT TO KNOW MORE?

For further details of the range, availability, and price, please use the link below to get in touch with your local Brüel & Kjær representative.

 

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