Phantom powered inputs

I need to record with a condenser mic using phantom power in one channel of my mixer, and my accoustic guitar played through an active DI into another mic input. However, I get a nasty low frequency noise which disappears when I unplug the lead from the DI. Any suggestions?

Can you shut off the phantom per channel, or is it on all the time?
Maybe the DI does not like 48 vdc.
Trahnsformer output?

A bit more information on your equipment might be helpful in diagnosing this problem - but I have occasionally come across this when there is no mains earth reference present on any of the items of equipment interconnected.

Almost the opposite of an earth (or ground) loop.....!

If your mixer has an external PSU (wall wart type) - which you were then feeding into (say) the sound card input of a lap top - there would be no mains earth reference anywhere.

Touch the tip of a jack plug of a guitar cable onto a screw head on the mixer - and touch the other end jack tip on some earthed metal work (water pipe, central heating radiator pipe. or screw head fixing on a UK 13 amp socket outplet).

Does the hum go?

Report back.....


JG

[quote author="StephenGiles"]I need to record with a condenser mic using phantom power in one channel of my mixer, and my accoustic guitar played through an active DI into another mic input. However, I get a nasty low frequency noise which disappears when I unplug the lead from the DI. Any suggestions?[/quote]

If the phantom power is only swtiched in groups you might need to use a single external phantom power box for the mic and turn it off at the mixer.