Preamplifiers for microphone cartridges
The output from a condenser microphone is a very high-impedance signal and is therefore very sensitive to the capacitive loads of cables. This makes it necessary to introduce a driver with high input impedance and low output impedance. Such a driver is called a preamplifier.
The frequency range of a preamplifier is determined by its electronic circuit and is typically more than 200 kHz at the high end and 1-10 Hz at the lower end. The lower end is determined by the input impedance of the preamplifier and the capacitance of the microphone. High microphone capacitance gives a low cut-off frequency.
The dynamic range of a preamplifier is defined as the range between the highest level that the preamplifier can handle without distortion, and the lowest level it can measure. The highest level is related to the preamplifier’s supply voltage, whereas the lowest level is related to the electrical noise generated by the preamplifier itself.
There are today two different preamplifier principles in the world of acoustics. One is the traditional type for externally-polarized microphones often referred to as the “LEMO” type because of its 7-pin connector and has become an industry standard. It is voltage driven and can handle high voltage signals up to 50Vpeak.
The other principle uses a Constant Current Power (CCP) supply and was introduced around 1996 to the world of high-precision acoustics. Before that, the quality of CCP preamplifiers was not as good as the voltage driven LEMO types, but this is not the case today. A CCP preamplifier uses a Constant Current Power supply, which must be between 2 mA and 20 mA (nominally 4 mA), to produce a constant nominal voltage level of 12 Volt DC (referred to as the bias voltage). The output signal from the microphone superimposes fluctuations around this DC level. The great advantage of CCP preamplifiers is that they use a two-wire system, where the signal is superimposed on the wire through which the current is kept constant.
This means that simple co-axial cables can be used instead of the more complex 7-core cables used with the voltage driven LEMO types. This is traded off by accepting a lower upper limit in dynamic range (due to the lower driving voltage of a constant-current source) which limits the maximum output signal to approximately 8 Vpeak, and the necessity of having to use prepolarized microphones. The range of available prepolarized microphones is still not as wide as for externally-polarized microphones, although GRAS was the first in the world to introduce 1/4” prepolarized microphones and have also released a 1/8” prepolarized microphone.
GRAS microphone preamplifiers are all small, robust units optimised for acoustical measurements with condenser microphones. They are all compatible with measurement microphones as defined in the international standard IEC 61094 “Measurement Microphones, Part 4: Specifications for working standard microphones”.
All GRAS preamplifiers are built around a small, thick-film precision amplifier with very high input impedance. The casings are made of stainless steel for maximum strength and durability with minimal sensitivity to vibration and microphonics.
They will work within their specifications up to a temperature of 70°C (158°F). Special versions for use at temperatures up to 120°C (248°F) are available on request. The only effect of elevated temperature is a slight increase in inherent noise level. This will change the lower limit of the dynamic range of the microphone/preamplifier combination, thus limiting the ability to measure very low sound pressure levels.
CCP (Constant Current Power) is the same as IEPE (Integrated Electronic Piezo-Electric) and CCLD (Constant Current Line Drive) and is compatible with many other constant current driven products such as Deltatron®, Isotron, etc.
DeltaTron is a trademark of Brüel & Kjaer
Freq range: 2.5 Hz - 200 kHz
Noise: 1.8 µV Gain: -0.30 dB
Special feature: General purpose
GRAS 26CA 1/2'' CCP Standard Microphone Preamplifier with BNC Connector
The GRAS 1/2" Preamplifier GRAS 26CA is a general purpose preamplifier optimized for use with prepolarized condenser microphones. It is a small,robust unit and uses a GRAS CCP power supply (ICP ®), e.g. GRAS 12AL. It has a very low inherent noise level, and a large dynamic range and a frequency response from below 2 Hz to above 200 kHz.
Freq range: 2.5 Hz - 200 kHz
Noise: 1.8 µV Gain: -0.30 dB
Special feature: High Temperature
GRAS 26CA-HT 1/2'' CCP High Temperature Preamplifier with BNC Connector
The GRAS 26CA-HT 1/2" CCP High Temperature Preamp (BNC) is a 1/2" CCP preamplifier for use with prepolarized microphones. It is optimized for high-temperature applications up to 120 °C (248 °F). It has a low inherent noise level, a large dynamic range and a frequency response from 2 Hz to 200 kHz.
Freq range: 2.5 Hz - 200 kHz
Noise: 1.8 µV Gain: -0.35 dB
Special feature: General purpose
GRAS 26CB 1/4" CCP Standard Preamplifier for Microphone with Microdot Connector
The GRAS 26CB 1/4" CCP Standard Preamplifier with Microdot Connector is a general-purpose preamplifier optimized for use with prepolarized condenser microphones. It is a small, robust unit and uses a GRAS CCP power supply, e.g., GRAS 12AL. It has a very low inherent noise level, a large dynamic range, and a frequency response from below 2 Hz to above 200 kHz.
Freq range: 2.5 Hz - 200 kHz
Noise: 1.8 µV Gain: -0.35 dB
Special feature: High temperatures
GRAS 26CB-HT 1/4″ CCP Standard Preamplifier with Microdot Connector
The GRAS 1/4″ preamplifier is a general-purpose preamplifier optimized for use with prepolarized condenser microphones. It is a small, robust unit and uses a GRAS CCP power supply, e.g., GRAS 12AL. It has a very low inherent noise level, a large dynamic range, and a frequency response from below 2 Hz to above 200 kHz.
Freq range: 2.5 Hz - 200 kHz
Noise: 1.8 µV Gain: -0.35 dB
Special feature: General purpose
GRAS 26CC 1/4" CCP Standard Preamplifier with SMB Connector
The GRAS 26CC 1/4" Preamplifier is a general purpose preamplifier optimized for use with prepolarized condenser microphones. It is a small, robust unit and uses a GRAS CCP power supply, e.g. GRAS 12AL. It has a very low inherent noise level, a large dynamic range and a frequency response from below 2 Hz to above 200 kHz.
Freq range: 2.5 Hz - 200 kHz
Noise: 1.8 µV Gain: -0.25 / +20 dB
Special feature: 0/20 dB gain, A-weighting and HP filters
GRAS 26CF 1/2'' CCP Preamplifier with BNC Connector, Gain and Filters
The GRAS 1/2-inch Preamplifier GRAS 26CF is a general purpose preamplifier optimized for use with prepolarized condenser microphones. It is a small, robust unit and uses a GRAS CCP power supply, e.g. GRAS 12AL. It has low inherent noise level, a large dynamic range and a frequency response from 2.5 Hz to 100 kHz.
Freq range: 1 Hz - 200 kHz
Noise: 1.8 µV Gain: -0.35 dB
Special feature: For low-frequency applications
GRAS 26CG 1/4" CCP Preamplifier with Microdot Connector, Low Frequency
The GRAS 26CG ¼″ CCP Preamplifier 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.
Freq range: 1 Hz - 200 kHz
Noise: 1.8 µV Gain: -0.35 dB
Special feature: Low frequency
GRAS 26CI 1/2'' CCP Preamplifier with BNC Connector, Low Frequency
The GRAS 1/2" Preamplifier GRAS 26CI is a preamplifier optimized for low frequency use together with prepolarized condenser microphones. It is a small, robust unit and uses a GRAS CCP power supply (ICP ®), e.g. GRAS 12AL. It has a very low inherent noise level, and a large dynamic range and a frequency response from below 1 Hz to above 200 kHz.
Freq range: 2.5 Hz - 200 kHz
Noise: 1.8 µV Gain: -0.45 dB
Special feature: For confined spaces
GRAS 26CK 1/2” CCP Standard Preamplifier with Microdot Connector, Very Short
The GRAS 26CK ½” Preamplifier, Very Short is a very small preamplifier optimized for use with prepolarized condenser microphones. It is a robust unit that uses a constant current power (CCP) supply. The 26CK has a very low inherent noise level, a large dynamic range, and a frequency response from below 2 Hz to above 200 kHz.
Freq range: 2.5 Hz - 200 kHz
Noise: 1.8 µV Gain: -0.45 dB
Special feature: For confined spaces
GRAS 26CS 1/4" CCP Standard Preamplifier with Microdot Connector, Very Short
The GRAS 26CS 1/4" Preamplifier is a very small preamplifier optimized for use with prepolarized condenser microphones. It is a robust unit and uses a CCP power supply. It has a very low inherent noise level, a large dynamic range and a frequency response from below 2 Hz to above 200 kHz.
Freq range: 2.5 Hz - 200 kHz
Noise: 1.8 µV Gain: -0.45 dB
Special feature: For confined spaces
GRAS 26CT 1/4" CCP Standard Preamplifier with SMB Connector, Very Short
The GRAS 26CT 1/4" Preamplifier is a very small preamplifier optimized for use with prepolarized condenser microphones. It is a robust unit and uses a CCP power supply. It has a very low inherent noise level, a large dynamic range and a frequency response from below 2 Hz to above 200 kHz.
Freq range: 2.5 Hz - 200 kHz
Noise: 1.8 µV Gain: -0.29 dB
Special feature: For both 1/2" and 1/4" microphone cartridges
GRAS 26AB 1/4''-1/2'' Universal Preamplifier with Integrated Connector
The GRAS 26AB 1/4" Preamplifier is a small robust unit optimised for acoustic measurementsusing condenser microphones. It has a very low inherent noise level, a wide dynamic range and a frequency response from below 2 Hz to above 200 kHz.
Freq range: 2.5 Hz - 200 kHz
Noise: 1.8 µV
Gain: -0.29 dB
Special feature: General purpose
GRAS 26AC-1 1/4" Standard Preamplifier with Integrated Miniconnector
The GRAS 26AC-1 1/4" Preamplifier 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 frequency response from below 2 Hz to above 200 kHz.
Freq range: 1 Hz to 200 kHz
Noise: 1.8 µV
Gain: -0.29 dB
Special feature: Low frequency applications
GRAS 26AI 1/2'' Preamplifier with Integrated Connector, Low Frequency
The 26AI is a 1/2" microphone preamplifier with integrated 7-pin LEMO male connector and 40 GΩ input impedance.
Freq range: 0.5 Hz to 200 kHz
Noise: 1.8 µV Gain: -0.25 dB
Special feature: General purpose
GRAS 26AK 1/2'' Standard Preamplifier with Integrated Connector
The 26AK is a 1/2" microphone preamplifier with integrated 7-pin LEMO male connector. The CCP equivalent is GRAS 26CA.
Freq range: 2.5 Hz to 200 kHz
Noise: 1.8 µV Gain: -0.25 dB
Special feature: Low frequency applications
GRAS 26AK-S1 1/2'' Preamplifier with Integrated Connector, Low Frequency
The 26AK-S1 is a 1/2" microphone preamplifier with integrated 7-pin LEMO male connector and 40 GΩ input impedance.
Freq range: 2.5 Hz - 200 kHz
Noise: 1.8 µV
Gain: -0.25 dB
Special feature: General purpose
GRAS 26AM 1/2'' Standard Preamplifier with 3 m integrated cable
The GRAS 26AM ½-inch Preamplifier is a small robust unit optimised for acoustic measurements using condenser microphones. It hase a very low inherent noise level, a wide dynamic range and a frequency response from below 2 Hz to above 200 kHz.
Freq range: 2.5 Hz to 200 kHz
Noise: 6 µV Gain: -0.29 dB
Special feature: Very short
GRAS 26AS 1/4" Standard Preamplifier with 3 m Integrated Cable, Very Short
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.
Freq range: 1 Hz to 200 kHz
Noise: 1.8 µV Gain: -0.29 dB
Special feature: For low frequency and low-noise applications
GRAS 26HG 1/4" Preamplifier with 3 m Integrated Cable, Low Frequency
The GRAS ¼″ Preamplifier Type 26HG 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 toabove 200 kHz.