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Radio Shack SPL meter
ETF supplies a high performance calibrated electret condenser microphonefor use in sensitive applications. The RS analogue or digital SPL meter may be used for ETF as well. This will not supply the same accuracy as the unit sold here but is recommended for applications where critical adjustment of frequency response is already done or not necessary. This unit has weighting curve adjustments that confuse a lot of users. This adjustment does not control the output, it only damps the meter movement. Download the calibration file below and open it as a microphone calibration file when using ETF with the RS unit. Please note that this is not a true "calibration file" because it is not calibrated for your unit. It will remove the gross response errors associated with this device. Typical differences between this unit and any random unit are within +/- 2 dB below 8 KHz, typically. This unit is virtually useless for accurate high frequency measurements. Other calibration files exist on the internet for this unit, these calibration files apply when reading the meter movement, not when taking data from its RCA output jack. These units are very constant gain below 500 Hz (flat frequency response) and do not require further low frequency calibration. RS analogue SPL meter calibration file
IBF-EMM8 Electret Measurement Microphone IBF-EMM8 Electret Measurement Microphone IBF-EMM8 omnidirectional measurement microphone Issue 1, February 2000 (C) Wolfgang Frank Ingenieurbuero f. Akustik, Elektronik, Messtechnik Alexanderstr. 66 68519 Viernheim Germany Tel. +49 (0) 6204 6608 Fax. +49 (0) 6204 6608 email: sales@ibf-akustik.de Website: http://www.ibf-akustik.de/ IntroductionGeneral DescriptionFeatures
Operational NotesWhy omniThe electret microphone Appendices
IBF-MP21 Microphone Preamplifier User Guide and Specificationsmicrophone preamplifier User Guide
(C) Wolfgang Frank Tel. +49 (0) 6204 6608 Design and Specifications are subject to change without
notice. Ask factory for technical specifications before purchase
and/or use. |
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Open the battery compartment and connect the batterie, accumulator or external voltage supply unit. Note: The mic-amp has a build in reverse polarity
protection avoiding damages caused by voltage supplies with
wrong configurated ouput voltage polarity |
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Check the power switch position and make sure it is in the off state. The power switch is part of the potentiometer function. |
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Change the bias supply for the microphone if an other than the factory setting is required. Note: While using the mic-amp with the EMM-8 mic and ETF you can leave the bias supply unchanged. Delivery state is CH1 (normally used as the measurement channel and marked red) - bias supply ON and CH2 (the reference channel and marked blue) - bias supply OFF. If you want to use CH2 (blue, trimmable) as an additional
mic channel with bias supply or using other microphones which
do not need biasing on channel 1 input please contact us for
a detailed description how those changes can be done. |
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Set the gain potentiometer to mid gain. |
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Using shielded microphone cable, connect a microphone to the microphone input channel (CH1-red) on the front panel. Do the necessary soundcard Line-Out to Mic-Amp-Ch2 (blue) connection. |
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Each channel contains an unbalanced Line-Output RF phono jack which are also located on the front panel. Connect the line outputs to the line inputs of the next device. |
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Be Careful! Turning power switch on or off, can produce a voltage spike
in the line outputs. Protect your ears, speakers and equipment
by being careful while the mic-amp line output is connected
to the next device. |
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Adjust the gain control with signal going into the microphone
to give the desired output level. The peak level indicator
can provide help in setting the right level. It has a characteristic
somewhat between that of a peak and VU control (short attack
and enlarged release time). It is a quasi reference and should
force you into a lower gain setting if necessary (Due to the
supply voltage dependent maximum output level the reference
is automatically corrected while the battery voltage drops)
. Even if the red LED is lighting, you are far from the mic
amplifiers clipping point. If the signal output level of CH 2 is far below that of CH
1 you have to increase input sensitivity by turning the trimmer
clockwise. (The input attentuater is a 20 turn trimmer to
give you better adjustability). Normally the adjustment trimmer
can be left unchanged on factory setting. |
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Be Careful and watch the gain setting! Is it realistic!
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The IBF-MP21 is a portable, battery-powered microphone preamplifier bias supply for electret microphones. Designed for 20Hz to 20kHz audio bandwidth. This quality mic pre is ideal for audio recording and acoustic measurement purposes such as speaker and roomacoustic measurements.
With its rugged mechanical and electrical construction, compact
size and high-quality components, the IBF-MP21 is extremely durable
and easy to use. This highly reliable mic preamp will provide years
of superb audio performance under regular conditions.
Maximum of 52 dB of gain, adjustable for accurate, repeatable gain settings. Channel 1 is adjustable by a single turn potentiometer.
In addition to this input channel 2 is variable by a 20 turn trimmer.
Clip indicator LED's show imminent overload condition. Unipolar detection, short attack time, long release time.
Internal battery power (9V) for convenient, low cost power. Works also with Nickel-Cadmium accumulator.
Power consumption is less than 25mA. Easy access battery compartment for quick battery changes.
Internally set bias supply voltage for electret-condenser microphones. (3V, 2.7kOhm)
Keep the mic-amp physically separated from other electronic equipment that produce electrical fields. As a high gain device, hum and noise pickup is possible through chassis and associated cable. Placing the unit away from transformers, power amplifiers, etc. will help to avoid pickup of those unwanted signals.
Signal connections
All connections on the mic-amp are made via RF phono jacks. Both the microphone input connectors and line output connectors are female.
The power switch is a built in function of the gain potentiometer. Due to the power consumption of approximately 25 mA and supply by battery power dictates applying power only as required.
When power is switched on or off, high level audio "pops" on the output connectors are likely.
This is a function of DC voltage turning on or off to the circuitry and can also be seen on the clipping indicator LED's.
Care must be taken to ensure that these "pops" do not damage equipment or ears associated with the mic preamp ouputs. It is a good idea to lower the sound level of the associated equipment.
Bias SupplyEach channel can be biased. Bias supply can be coded inside of the chassis nearby the front panel.
When an internal bridge is soldered in the +3V is applied via 2.7kOhm resistor to the mid pin of the RF phono jack. This 3V bias voltage should allow virtually all mics to work correctly (mics with electret capsules and no additional circuitry inside).
While using microphones that do not require bias, the bias bridge
of the belonging mic channel must be unsoldered or cut out.
The Mic-Amp has a build in clipping indicator in really two complete seperate channels that can provide assistance in setting the gain control.
It has a characteristic somewhat between that of a peak and VU
control (short attack and long release time). It is a quasi reference
and should force you into a lower gain setting if necessary. Even
if the red LED is lighting, you are far from the mic amp's clipping
point.
The IBF-MP21 is designed to operate on one 9 V battery or accumulator or external 9V power supply (It contains a reverse polarity protection device).
Note: The audio performance, respectively the maximum output voltage
swing depends on the batterie voltage which drops down during it's
life-time. This is not the case when using an external electronically
stabilized voltage supply. Using a 9V or rather 8.4V accumulator
results in short service.
Appendices
CE Conformity Statement
I declare under my sole responsibility, that the product microphone preamplifier "IBF-MP21" combined with the microphone "IBF-EMM8" is in conformity with the following european standard: EMC Directive no. 89/336 EEC. This is documented by accordance with the following standards: EN 50081-1 Viernheim/Germany , 06 . 06 . 2000 (This decalaration of conformity is suitable to the European Standard
EN 45014, Limited Warranty
IBF (engineering office Wolfgang Frank) warrants the IBF-MP21 preamplifier against defects in material and workmanship under normal use and service for a period of one year from date of original purchase. We will repair or replace the product at no charge provided that the product is returned, shipping prepaid, to the manufacturer. This warranty does not apply if, in our opinion, the product has been damaged due to abuse, misuse, misapplication, accident or as a result of service and modification by other than an authorized dealer. For all service, including warranty repair, please send the IBF-MP21, along with proof of purchase date to:
Wolfgang Frank Tel. +49 (0) 6204 6608 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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