*** Quoting Donald Quarles to T Owen dated 03-23-96 ***
> 
> DQ>> I have a mackie mixing board 16 channel being run in stereo and
> DQ>> also a stereo graphic E.Q. and a processer and Bose in the
> DQ>> ceiling speakers and a 1000 watt per channel power amp and also
> DQ>> for the motiores i use a pevey head 300 watts per channel. what
> DQ>> the problem is when i turn the thing up i get a low freg. hum and
> DQ>> can not fiqure it out when no one is using the system is hum
> DQ>> likes a boat motor off in a distance..
> 
> TO> Sounds like a ground loop to me. Is everything plugged into 
> TO> the same leg of AC power? Are you running long unbalanced 
> TO> lines? Are signal cables (esp. unbalanced) running paralell 
> TO> to AC feeds? Tell me how things are wired up, and I may have 
> TO> some ideas. Take care. 
> 
> well thank you first for replying to me. This is in our church
> we have had this hum since i have been there we havbe a 100'
> snake runnign from the back of the building to the stage on the
> stage we have 16 plugs all sheilded and grounded the snake is ran
> through the ceiling in a plasitic pipe. then as they come to the
> back they go into the sound room and hook up to the XLR plugs on
> the mackie now for the monitors we have a cable coax running
> about 65 foot coming from the stage which has two peveay's
> montiors and then through the 65 foot line and into the peavey
> montior head. and in the sound romm we have a E.Q, Power bass
> amp. and effects machine for speakers they have insatlled the
> bose with the sub woofer system.. that is it in the nut shell and
> kind of help would be apperacited.
> 
> Donald Quarles A.K.A BAD
I do a lot of live stuff with portable systems (several times a week).  What 
I do to eliminate this problem is:
a. Power my console and effects/processing rack from the exact same power 
source as my power amplifiers... in my case this involves running a 100' 12/3 
SO cord to the power amp rack from the console.
b. Require the use of an active direct box with ground lifts for keyboards, 
bass etc. direct inputs (no cheap transformers), to eliminate ground loops 
from different circuits that power those items. Rule of thumb is that if it 
plugs into the snake, it either has a ground lift/isolation or it's on the 
exact same power source ... 
This usually does it for me .... however .... sometimes neither of those 
things eliminate the problem ... I generally turn everything up a little and 
start un-pluging stuff from the snake one by one till the problem disappears.
If I'm standing there with nothing plugged into the snake, then I starts 
looking ....
--- T.A.G. 2.7c Standard
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