[LAU] ground loop hell

[Len Ovens]

On Sun, 8 Feb 2015, jim wrote:

> ( hoping this helps someone(s) )
>
>    Best, or at least good, practice suggests ensuring you use a
> single earth ground. Practically this means using a single
> receptacle with a power strip with enough receptacles for all
> your equipment. This model forces separate ground paths for
> each device to a single, common grounding point. (15 amps
> at 110VAC is usually enough power for a band and PA and
> recording equipment; think of the entire setup as a single
> device comprising amps, mics, outboard equipment, mixers,
> and so forth: all one frankenstein device.)

This is what we did. This building used to be the "Rod and Gun Club" in 
the area. It has been extended three times (that I can tell). There are 
some (more) renovations pending and so the original outlet the mixer used 
was boarded off at this point. So a cord was run to the next nearest 
outlet which is part of an anix (the roof is different which makes it 
obvious). This is from a different power box and (as is now clear) ground 
point. There is already a hole into the attic both above the mixer and 
above the stage where the snake runs through. The cord we were using for 
the mixer power was more than long enough and so we ran it through the 
same holes and plugged it into the same outlet as the stage gear. Ground 
loop gone. Nice clean sound :)

>    Note that both balanced and unbalanced signal cables
> connect to device frames, and therefore to earth ground.
>    In the case of balanced cables, the frame connector (the
> sleeve for phone plugs and pin 1 for Cannon XLR three-pin
> cables) extends the Faraday shield of the frame to the sheath
> conductor over the two signal wires.
>    In the case of unbalanced cables, there is only one signal
> wire (tip of a phone or RCA plug); the sheath conductor
> provides a current path for both the signal return and the
> earth ground.
>    Balanced is better, if possible.

Most of the new snakes are ballanced both ways... this one is older.

>    If you're using unbalanced cables, then your only fix is
> to lift the ground of the power cables for all but one device
> so that all the other devices must make their connections
> toground through the sheath conductor of the signal cables.

Not going to happen. Using one outlet works fine in this case.

As part of the reno, (which includes new wiring to code BTW) I am hoping 
to put in tech power (isolated ground) for all audio. We may need more 
than one breaker, but the grounds will be shortest physical path I can 
get. (even if I have to run extra cables just for ground) It is nice to 
have some say when doing ground up stuff.


--
Len Ovens
www.ovenwerks.net