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Phantom Power Microphone - What are they and how do they work.....Typical Circuit Diagram

Some microphones (capacitor types) need a battery to make them work since there is some inbuilt electronic circuitry to amplify the signal. Cheaper microphones have provision for a single AA size battery only, where professional grade quality microphones are almost always phantom powered. This is a term to describe powering the microphone remotely from the microphone mixer via the microphone lead so that a battery is not needed. Obviously this improves reliability as there are no batteries to go flat. Dynamic microphones do not have this provision and therefore produce MUCH smaller outputs. Small outputs sent along long lengths of microphone cable tend to pick up noise, even if true balanced line working is used since small variations in cable construction lead to balancing errors which allows the ingress of electrical noise and interference. Hence phantom powered microphones have the advantage of sending much larger signals down the wiring which means less probability of interference = better. All lead pluggable microphones featured on this site are phantom powered.

How do I check if my microphone mixer has phantom power?

The first thing to check is the microphone lead wiring. If it has a single signal wire and outer screen, then your microphone is unbalanced and NOT phantom powered. If you have two signal wires and an outer screen then it MIGHT be phantom powered - do the following check:

It is very easy to check with a simple dc voltmeter. Turn the microphone mixer on with all microphone volumes turned to minimum. Unplug a microphone and test for a dc voltage between 12 and 50 Volts measured between either signal wire (Pins 2 or 3 on an XLR plug) and earth (Pin 1). If the voltage exists, then any phantom powered microphone will work fine. Some microphone mixers have a switch or set of links to enable phantom powering - check the handbook.

Be aware that plugging or unplugging a phantom powered microphone with the channel gain set to anything other than zero, might cause large transients that could damage your equipment and/or speakers and is most certainly unprofessional. Don't do it!

What if my mixer has not got phantom power?

In this case you would have to stick with dynamic type microphones or use batteries in capacitor types. A better solution would be to invest in a new microphone mixer and best of all - fit an Automatic one to make it easier. Failing that, you can modify your existing mixer using the Circuit Diagram to provide phantom power for each microphone, though be warned, this is a specialist job (you will need a separate circuit for each microphone) and ideally uses 0.1% or better matched resistors between signal lines and filtered power supply.

Photos.....ATM33a.....2 x ATM33a on Goosenecks.....Rostrum Mic AT915.

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