Avid profile weird distortion problem

I recently had a gig from hell. System teching FOH for an outdoor festival and it rained, rained and rained and console was right at the front of the tent so we needed to tarp it often.

(and we had a useless security guard who saw no problem in letting in 15/20 punters into our tent whilst we were trying to work and keep gear dry..).

Ok.. so i've got a profile with FOH and stage rack and using 4 core snake to link. 25 inputs from stage all clean. We're sending back 4 auxes to stage for monitor purposes; we go out of 4 outputs on the stage rack and into the monitor console.

During our tech line check all good; during BE's sound check whilst other act on stage, all good.

Then the act starts and my mons guy tells me we've got massive buzz coming down all 4 lines we're sending. We solo the send on the profile and it's clean.

So I try re-routing to outputs on the second IO card, no change.

I then try going out of local analog outs and run down an analogue core to stage, same issue.

If I was on the desk I'd try a few other things but I wasn't on the desk; BE was busy getting his mix together (no show file, he was told we had an M7..) I could have tried going out analogue local and back in local and see if I get buzz on the input.

At one point I noticed the CD player was still going; that was going AES into the local 2 track return. I stopped the CD player.

A while later the stage guys told us that the signal came good.

It was just too weird. I'm thinking it's either the AES input was causing some issues (but why returns to stage not everything else ?) or a bit of moisture got in.

Hmm.. after writing this out the only thing we didn't change was the monitor console (m7), or channels on the console; that was in a well sheltered area, no rain issues.

Has anyone had anything similar ?

Also to make my gig bad was a small digital console used for DJ's dropping 10dB and then going normal again many times a minute; then settle down; then do it again etc. Like how some amps go into thermal protection - drop signal for 3 seconds or so; then go back to full only to drop again. I ended up going out of console auxes instead of mains 'cause inputs metered consistently but main output meters dropped.

Andrew
 
Buzzes, rain, festivals and crappy security make for easy problems to become way too complicated.

Did you have any transformers to put between the stage rack and the M7?

Anyone have a QBox, or at the very least a spare 58 and a turnaround on site to verify the send signals are clean coming out of the stage rack?

The CD at FOH may have done something with the clock sync coming in the digital in (the only time I've used external clocks on profiles is to sync up multiple stage racks, as the cards in the brain never seem to work for me.)

Sounds like there was a voltage difference between the grounds of the M7 and your stage rack.

I carry a handful of Rapco IsoBlox just for these situations. A decentish (*cheap*) line level transformer. If you have any low freq content (under 115hz), I'd use a better transformer. Price/size/weight is right for me for a quick buzz fixer for talkback, monitor and record feeds, etc.

BRad
 
Re: Avid profile weird distortion problem

The M7 and stage rack were on the same distro; not sure about same circuit. Maybe some moisture did something to change the ground potentials at the stage end.

I see what you're saying with the Q-Box; I now see the need for one in situations like this; i'll have one just in case for the next gig.

The company I work for normally has a bunch of radial ISO's on hand so if the q-box says clean and console says dirty, we'll insert.

Thanks for the advice.

andrew