PRÉ-AMPLIFICADORES DE MICROFONE

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

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 

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

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.