[LAU] ground loop hell

[David Christensen]

On 02/11/2015 02:06 PM, Fons Adriaensen wrote:
 > That [stage amplifier] isolation is worth having, always. In modern
 > PA systems it's done by using optical fibre snakes. If ever you
 > consider replacing your current gear that would be a good option.

On 02/12/2015 12:53 PM, Len Ovens wrote:
> I will order the boxes (I think 6 lines worth will cover anything
> possible with the mixer we have). I was going to put in a network cable
> anyway (if we use it right now or not) but could aslo put in optic
> line(s). Are they subject to degradation with time if not in use? It is
> not a long run at less than 100ft (this includes running it up above the
> ceiling and dodging open rooms etc. The dx from stage to mix is less
> than 50ft.)

I assume you mean 6 additional digital channels over one Ethernet cable 
to supplement your existing snake (?).


I suspect that migrating to digital piece-by-piece could be a painful 
and expensive experience if you don't know your exact final 
configuration before starting.  It's a complex and highly technical 
field.  The product lines have short life cycles.  Compatibility is 
tough.  Maximum cable distances are surprisingly short (but should be 
enough for a small venue).  Copper networking equipment is also subject 
to ground loops (fiber should not be).  Specialized tools and equipment 
are required for installation, maintenance, and trouble-shooting.  And, 
very few people are going  to be on top of the learning curve.


For the small venue that you've described, I'd recommend a balanced 
analog system throughout, with converters located at unbalanced gear as 
necessary.


But if you're going to pull Ethernet cable, understand that cable is 
cheap (1,000 ft. box of Category 5e riser cable is $50~100).  It's the 
labor and/or raceways, enclosures, and, especially, equipment that add 
up quickly.  Make sure you understand the RFI/EMI interference issues 
and prevention measures.  (Similar comments apply for analog audio.)


David