Hum Problem

  • Thread starter Thread starter blaydonrob
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blaydonrob

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Hi all

I have recently bought a Scarlett 2i2 and a Rode NT1-A mike but when I switch on phantom power I get a really loud hum. I have eliminated wiring/cabling etc and tested other mikes which are all ok. Would buying a balanced mike amp to insert in the chain between the mike and the audio interface (so that the Scarlett phantom power was not needed) solve the problem or am I missing something simpler (and cheaper :-)).

Rob
 
FFS do not buy anything else!

Both those items are very well respected and should work faultlessly together.

You say "other" mics are fine but have you tried phantom powered mics? DO NOT switch on phantom power with other, dynamic mics until the problem is resolved.

Have you tried the whole rig in another computer? I suspect you see a dirty USB supply but why that should just affect spook juice I cannot say.

Silly question I know! But have you tried a meter on the phantom power? If it is 48ish volts, switch to AC, should be buggerall.

Dave.
 
I suspect the USB port, too. What compute are you using? Is there anything else plugged into the USB ports?

Also, are you sure it's 'hum' and not room noise or the computer fans? Post a clip of the sound.
 
Low Phantom power can cause hum on some mics, so as eec83 said, try to check the phantom volts with a meter.

Cheers
Alan.
 
Cheers Dave - as you say the products are good and should work - will try your suggestions. Much appreciated.
Rob

---------- Update ----------

Hi Chili

I'm using an iMac with all 4 USB ports being used.

Rob

---------- Update ----------

Cheers Alan - will do
Rob

---------- Update ----------

Cheers Alan - will do
Rob
 
"I'm using an iMac with all 4 USB ports being used.

Rob"

Get a PC! (always wanted to say that!)

Dave.
 
blaydonrob said:
lol
Click to expand...

Hey Blaydonrob,
I was talking about this in another thread. I doubt it's a power limit issue, but it'd be easy enough to prove otherwise.
Try your interface with all other USB devices unplugged.
If that's no good either try it in a PC or, even better, try with a powered USB hub.

If that kicks it into life you'll know it's a power issue and your options are
  • Buy an external phantom power supply
  • Buy a powered USB hub
  • Buy a different USB interface with external power supply
  • Buy a firewire interface
  • Buy a pc (that's for you, Dave) ;)


Big +1 for buying/using a meter. Those things are invaluable.
 
Thanks mate - I'll definitely try the powrered USB
Rob
 
Tiny point.
Some interfaces will not work on a hub, powered or nay so plug the AI into a USB port and run everything else off the hub.

Dave.
 
Hi guys

Problem solved but it took another bit of hardware to do it. I had a Soundcraft Compact mixing desk with phantom power so I introduced it into the chain between the mike and the Scarlett 2i2. The hum disappears when I use the phantom power from the desk rather than the 2i2. Thanks to everyone who replied with suggestions.
Rob
 
blaydonrob said:
Hi guys

Problem solved but it took another bit of hardware to do it. I had a Soundcraft Compact mixing desk with phantom power so I introduced it into the chain between the mike and the Scarlett 2i2. The hum disappears when I use the phantom power from the desk rather than the 2i2. Thanks to everyone who replied with suggestions.
Rob
Click to expand...

That would suggest either an actual fault with the 2i2 or maybe an inherent problem with its phantom power supply?
We have a Focusrite "man" around in Simon, perhaps he could comment?

It might well be that the NT-1 is going to catch a lot of AIs out? It draws nearly 6mA from the XLR and that is some 3 times the current most "budget" capacitor mics demand. 5.7mA is still well within the standard of 10mA but problems of poor current capability, when all 8 say channels of a mixer are fully loaded, have been flagged in the past.

One to watch methinks?

Back of envelope calculation: If an AI has two mic amps each capable of the max 10mA that translates to a current pull from the USB port of 200mA even if the converter was 100% efficient. It won't be so in practice the phantom power supply would need around half the available current at ~250mA.

I would doubt therefore that ANY solely bus powered USB AI will be capable of the full fat spook juice specc' and some will fall well short......Roll on USB 3 AIs!!!



Dave.
 
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