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11 ULTRAGAIN PRO MIC2200 User Manual
microphone
preamplier
microphone
microphone
transformer
+48 V
+48 V
microphone
cable
microphone
amplier
output
A
B
Fig. 5.1: Functional diagram of phantom power supply
5.1.5 Phantom power
Condenser microphones need a specic supply voltage polarizing the condenser
diaphragm. This voltage can be furnished from an internal battery, or an external
power supply that is either connected directly to the microphone or supplies
the voltage through the microphone cable. In practice, this technique is usually
referred to as +48 V or phantom power supply, and uses the microphone cable to
carry both the audio signal and the supply voltage required for the microphone.
Please read this chapter thoroughly: phantom power can damage the
microphone, if used improperly.
We speak of phantom power when a microphone cable is used to carry several
signals, with a DC voltage “layered” on the actual audio signal. The typical
phantom DC voltage is +48 V, which is applied both to the positive (pin 2)
andnegative inputs (pin 3) of the XLR connector, using current-limiting resistors.
Asthe phantom voltage is split up in a balanced conguration among the signal
leads, there is no need to apply it directly to the microphone transducer or the
microphone itself, where it could damage the transducer and/or capsule. In an
unbalanced conguration, DC voltage would be applied directly, which would
inevitably lead to disturbing noise or could even damage the electronics.
To eliminate this risk, the BEHRINGER ULTRAGAIN PRO automatically disables the
unbalanced phone jack in MIC mode. Microphones can thus only be connected to
the XLR connector.
Never switch on the +48 V supply when you use unbalanced microphones, as this
could cause electrical damage.
Some people hold that the sound of dynamic microphones is aected when the
+48 V supply is on, or that ribbon microphones cannot be operated from an input
equipped with +48 V phantom power. None of these statements is true. As a
matter of fact, problems of this kind are caused by one of the following reasons:
1. When the output transformer of the microphone suers from a short circuit
or leakage current at any point, disturbing noise, clicks or hum can occur.
Inthis case, you should have the microphone repaired.
2. When you connect a microphone while the +48 V supply is switched
on, itcannot be guaranteed that both signal leads of the XLR connectors
establish the electrical contact precisely at the same point of time.
Therefore, detrimental current could ow because the connection is
temporarily unbalanced. We recommend that you switch o the +48 V
supply before you attempt to connect a microphone.
◊ Please make sure that you are using an appropriate microphone before
you switch on the +48 V supply. Read the operating instructions
accompanying the microphone. Some condenser mics might need
another type of power supply, older dynamic microphones could be
damaged by the +48 V voltage, and unbalanced microphones should
never be operated in combination with a +48 V power supply.
5.2 The ULTRAGAIN PRO as a level translator
Semi-professional devices in hi- and home recording environments are usually
operated with a nominal level of -10 dBV (0.316 V), while the level used in studios
is 0 dBu (0.775 V) or +4 dBu (1.23 V). So, when you connect devices of both types
to each other, you should do this via some kind of level translator.
The BEHRINGER ULTRAGAIN PRO is excellently suited for this application. In LINE
mode, the OUTPUT control allows you to raise or lower the input signal level
by as much as 20 dB. The functions PHASE REV. and LO CUT are also enabled in
thismode.
5.3 The ULTRAGAIN PRO as a
direct-injection box
When electrical signals delivered by instruments such as guitars, keyboards, etc.
are transported over long unbalanced lines, the transmission quality may be
aected by hum or other interference signals induced in the cable. This problem
is usually encountered in studio or stage environments, where long cable lengths
and magnetic elds of great magnitude may produce interference.
So-called direct-injection (DI) boxes are used to counter this eect: the DI box
converts the unbalanced signal coming from the instrument into a balanced
signal that is sent over the line. Interference induced in balanced cables is then
eliminated by a subsequent dierential amplier (as explained in chapter 3.3).
Using the ULTRAGAIN PRO for this kind of application is easy. Simply connect the
line output of your keyboard to the phone jack input on the ULTRAGAIN PRO.
Thenuse the ULTRAGAIN PRO’s balanced output to send the signal to a stage box
or other transmission chain. You can use both the XLR and phone jack connectors
of the ULTRAGAIN PRO. Set the unit to LINE mode, with any additional functions
switched o (an exception being the OUTPUT control which can be used to adjust
levels, if necessary).