Behringer MIC2200 사용자 설명서

ULTRAGAIN PRO MIC2200 User Manual

microphone

preamplifier

microphone

microphone

transformer

+48 V

+48 V

microphone

cable

microphone

amplifier

output

A

B

Fig. 5.1: Functional diagram of phantom power supply

5.1.5  Phantom power
Condenser microphones need a specific 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) 

and negative inputs (pin 3) of the XLR connector, using current-limiting resistors. 

As the phantom voltage is split up in a balanced configuration 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 configuration, 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 affected 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 suffers from a short circuit 

or leakage current at any point, disturbing noise, clicks or hum can occur. 

In this case, you should have the microphone repaired. 

2.  When you connect a microphone while the +48 V supply is switched 

on, it cannot 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 flow because the connection is 

temporarily unbalanced. We recommend that you switch off the +48 V 

supply before you attempt to connect a microphone.

Semi-professional devices in hi-fi 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 

this mode.

When electrical signals delivered by instruments such as guitars, keyboards, etc. 

are transported over long unbalanced lines, the transmission quality may be 

affected 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 fields of great magnitude may produce interference.
So-called direct-injection (DI) boxes are used to counter this effect: 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 differential amplifier (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. 

Then use 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 off (an exception being the OUTPUT control which can be used to adjust 

levels, if necessary).