Use Phantom Power Mics with Consumer Camcorders
Improve recorded audio on Video Shoots with P48 powered Microphones.
Aug 12, 2008
Using good quality professional or in some cases studio microphones can offer the video recordist a significant boost in sound quality. However, professional microphones tend to come with balanced XLR connections whereas much consumer and semi-pro gear comes with 3.5mm jack inputs. If internally powered via a battery like the Sennheiser ME series using a K6 adapter, all that needs doing is connecting the balanced microphone to the unbalanced input correctly. However, if the microphone is designed to be powered from the mixer/recorder along the cable, then this power needs to be injected into the microphone cable for the microphone to work at all. The 48V phantom power must also be kept out of the camcorder!
Phantom Power Unit
A phantom power unit injects a +48V supply into the microphone cable, via a matched pair of 6.8k resistors onto pins 2 and 3 of the XLR cable, with the 0V terminal of the power supply connected to pin 1. In studio operation this is normally supplied by the recording mixer or the field recorder, but a phantom power unit can be inserted into the cable and powered from internal batteries or a mains adapter. The phantom power unit presents a socket into which the microphone is plugged, and a plug which accepts a line plug which goes to the recorder. Most phantom power units put the 48V supply on the microphone-facing socket only and isolate it from the plug going to the recorder. It is, however, worth one final check with a multimeter to make sure that there is not 48V on the plug. If this is confirmed, then any of the techniques described in Wire a Balanced Microphone to Unbalanced Inputs can be used to connect the phantom power unit to the camcorder microphone input. Alternatively, if the camcorder already has XLR inputs than a straight XLR extension cable can be used.
The schematic for a phantom power unit is simple, but the price of commercial phantom power units from internet music supply houses like Thomann is in the order of €20 so it is not worth the bother to make one. Video makers should ensure that their phantom power unit can be powered from batteries. Ideally the batteries should be contained within the unit, and many video shoots will be in locations where AC mains power is not easy to provide.
Having phantom powered input available on a video shoot can be reasonably cheap even if the video recorder only presents consumer-type 3.5mm sockets. This greatly widens the range of microphones that can be used, and for some specialised circumstances it may be worth renting something like a long gun microphone for difficult audio situations.
