Emu XL-7 & MP-7 User's Group

The first thing to do is figure out what kind of hum you have. If you
have 60hz/50hz (depending on your local power system) it will be
approxamately the same tone as the third A below Middle C. This is a
ground problem, the most common source of hum. You can reduce the
likelyhood of a ground problem by making sure all connectors in the
system (audio, power and control) are clean and all power is coming
from one good clean source. 

Ground issues can be divided into two categories, poor ground and
ground loops. A poor ground is generally the result of bad or dirty
connections. This is like removing the ground wire from your
turntables to your mixer. 

A ground loop is when signals start resonating on a section of the
ground path that connects to itself in a loop. To fix this you need to
make sure that there is one and only one path to ground from any piece
of equipment. For example, an instrument that sees ground from the
power cable and through an audio out through the mixer into the
mixer's power cable could have a problem. It may not, but it could.
These loops can get complex if you are not carefull and increasing
complexity leads to an increasing chance of hum. Ground running from
an instrument to the mixer to some effects to another instrument will
almost definitely cause a problem.

To track this down, unpulg all of the audio inputs from the mixer.
Then start pugging things in one at a time until the hum comes back.
Now see if you can unplug something else again to make the hum stop.
Once you have found the culprit wire(s) you need to somehow disconnect
ground between the instrument/wire and the mixer. If your problem is a
balanced cable it is easy, just disconnect the ground (shield, sleeve
or XLR pin 1) at the instrument end of the cable. If the culprit is
unbalaced you will need a "DI box" or isolation transformer to
seperate the ground signal.

If the tone is high pitched the problem is usuall interference from a
noisy piece of equipment. Try turning things off until you find what
makes the hum go away. Dont just try things in the rack, try things
around the room. Flourecent lights, dimmer switches, computer monitors
and cell phones are some the more common culprits. Once again, good
clean connections and a good clean power source will always help
(especially if it is noise from something like a flourecent light or
dimmer switch).

Hope this is of some help,
Ezra


--- In xl7@y..., "mikexl7" <mikexl7@y...> wrote:
> I am in a situation where all my cables are packed into a road 
> case.  I have all that is balanced using balanced cables but there 
> still is some hum.  I think some of it is off my new mixer (alesis 
> studio 12R) before this mixer i was using a mackie 1604vlz.  I think 
> it had a lower noise floor.  Almost all my cables where made by me 
> and are shielded and of good quality but what can i do about the 
> power cables?
> 
> Any advice other than the power conditioner.
> I am totaly packed for room in this box so I would have to mount it 
> in the back some how.  so other than that what can I do?
> 
> Thanks for any help.
> 
> Mike G.
>