[LAU] Terrible mic ground noise

[Len Ovens]

On Sun, March 31, 2013 7:06 am, jonetsu at teksavvy.com wrote:
> Hello,
>
>    There is a very bad ground noise when I connect the M-Audio pulsar
> mic into a mic input of the 1010LT.  As soon as I touch the mic, the
> ground noise disappears.  Complete silence.  But then, try to play bass
> like that.  The mic goes through a Radial JDI passive direct box.  It
> has the 15dB pad on because it makes a bit less ground noise.  I tried
> various settings on the DI box, bit none gets rid of the noise.

Where does the mic get its power from? The M-Audio pulsar is a phantom
powered mic, the passive DI does not supply power and also would block
power from going through. The 1010lt does not mention sending phantom
power... does the mic have a battery? (the user guide says it requires
phantom power, so no battery)

Why a DI? A DI is not for a mic, the mic needs a mic pre. The 1010lt has a
mic pre, so all you need is a phantom power box in between. I do not know
if the pulsar will work with only 18v (most battery powered phantoms are 2
9v batteries) or if it needs the full 48v.

>From what you have said above and from looking up the HW you are using,
you should not be getting any audio through the mic at all. So if you turn
the gain up high enough you might get hum.


>    The electric plug has only two prongs.  I though of getting some

What electric plug? The gear above would only have power to the computer.
Is the computer a laptop (doesn't make sense, it has a 1010lt PCI card in
it) All desktops have a standard grounded power supply. If yours has had
the ground removed replace the power cable. (for safety if nothing else)
They are dirt cheap and lots of people have never been used ones hanging
around somewhere anyway... as in free.

So either you have not described you gear fully/correctly, or you are
using the wrong hook up.

However, assuming you have just described your setup incorrectly... and
there is a phantom power box and not a DI. My first guess is a bad mic
cable from the phantom box to the audio card. Your grounding path _should_
be:

 - Ground rod (many houses use the city water for this which is fine)
 - house wiring (this may be something to check, it is possible the outlet
you are using for your computer is no tproberly grounded)
 - computer through it's power cord
 - 1010lt pin 1 in the xlr connector or sleeve if you are using line in
with mic pre.
 - mic cable shield to phantom box
 - mic cable shield to mic.

Adding another wire for ground should just add a ground loop and more hum,
better to fix the problem.




-- 
Len Ovens
www.OvenWerks.net