Mixers/Consoles Noisy A&H GL2400?

gafftaper

Senior Team
Senior Team
Fight Leukemia
We have installed a new video system and we have discovered lots of background noise. You can't hear it in the house, but my video guy is complaining about all the noise. Turns out my two year old GL2400 is putting out about 30db of noise with everything off. Is this typical? Is there anything that can be done?
 
Re: Noisy A&H GL2400

My GL2400 goes out into an Audia EXPI to be converted to cobranet then goes over to my Audia Flex DSP. I had a guy here the other day doing some programming on the DSP and there was all this noise around 30db (or more) showing on the internal meters of the DSP. We had everything off on the board. I disconnected the board from the EXPI and it all went silent. So it seems pretty clear the problem is in the board.
 
Re: Noisy A&H GL2400

hmm... is it a separate output from the mains? Or are you just splitting the signal before/after the A/D into cobranet?
 
Re: Noisy A&H GL2400

Do you get any buzzing through the speakers? I'm thinking ground.


I haven't heard any buzzing. It's power runs through a Tripp Lite surge suppressor. I'll try running it straight to the wall on another circuit when I get a chance next week. Any other ideas?

hmm... is it a separate output from the mains? Or are you just splitting the signal before/after the A/D into cobranet?

I have all four groups plus the the 3 mains all going through a short snake into the A/D. When the guy had his laptop connected to the DSP and I disconnected the lines from the back of the board all the noise went away on those DSP meters. Sadly I didn't cross check to rule out the snake was the source of the problem but I think it's a pretty good quality snake. :(
 
Last edited:
Re: Noisy A&H GL2400

See if disconnecting the VIDEO drops the noise floor. How are you feeding the video via coax or ?? . Sometimes it can be the video ground vs the audio ground.

Sharyn

Sharyn
 
Re: Noisy A&H GL2400

I haven't heard any buzzing. It's power runs through a Tripp Lite surge suppressor. I'll try running it straight to the wall on another circuit when I get a chance next week. Any other ideas?



I have all four groups plus the the 3 mains all going through a short snake into the A/D. When the guy had his laptop connected to the DSP and I disconnected the lines from the back of the board all the noise went away on those DSP meters. Sadly I didn't cross check to rule out the snake was the source of the problem but I think it's a pretty good quality snake. :(

Try each output individually too.
 
Re: Noisy A&H GL2400

See if disconnecting the VIDEO drops the noise floor. How are you feeding the video via coax or ?? . Sometimes it can be the video ground vs the audio ground.

Sharyn

Sharyn

We have two Audia Flex DSPs. One in the Audio rack and one in the video Rack. They apparently have a sort of joint brain which shares audio information back and forth between both units in order to record video, playback Blu-Ray, and for a teleconferencing system.
 
Re: Noisy A&H GL2400

I am not familiar with this setup, just that I have seen cases where a signal that is not a problem on the video side of things will show up on the audio side because of the common ground. Coax of course is not a balanced signal, and the long coax shield and any video device along the way that has a potential ground signal problem can feed this ground back into the system, and if the audio and the video are ground connected this can cause a problem.

Again might not be the issue, but might be worth a try. For Coax video I have used a video hum eliminator transformer.

Sharyn
 
Re: Noisy A&H GL2400

So as I understand it, you take analog into the AudiaFlex and then that spits out Cobranet which is converted back to analog in video land. Video source is utterly independent of audio.

Can you verify that the console is at fault? Merely disconnecting the console does not eliminate the DSP as the noise source. Can video dude derack his stuff and do a direct connect to the console and see if that changes things?
 
Re: Noisy A&H GL2400

Get better dimmers. It's always the dimmers.:twisted:
 
Re: Noisy A&H GL2400

By any chance is the video connected to a cable tv distro system to the rest of the school? is the cable tv also connected to a cable supplier.

Again this may NOT be the issue, and it could be in the console, but the fact that you see the noise but don't hear the buzz leads me to guess that it is something outside the normal audio range, and also usually the first thing I check is the last thing I changed. So you comments re the video update has led me to think in that direction

I have seen situations where since eventually you probably have your video and your audio come together, IF there is a connection to a cable tv setup and especially if it is also a feed that combines with standard cable tv what you can have is the signal ground from the video from the cable company can go all the way back to the cable tv system and so you can have a situation where you do have some sort of a ground loop set up.

Sharyn
 
Re: Noisy A&H GL2400

With video land being on the other end of a cobranet feed, it is very unlikely you are getting and grounding issues.
Going on your saying the DSP meters went to -0- when you unplugged the snake, I would start by checking the individual inputs on the audiaexpi, then check each individual output on the A&H board and try to isolate the issue.

Also, i know you likely tried this, but you did reboot the Audia flex. They are great units, but occasionally like any computer they can lose their place and cause all sorts of wierd issues and havoc (that's a whole other story for me)
 
Re: Noisy A&H GL2400

Wow lots of great ideas here I'll try to answer some questions...

In Video Land, we have a four robotic camera recording system, blu-ray playback, a video conferencing system, output to the house Panny projector, output to lobby video monitors, and output to stream over the internet. While we do have a campus TV station, I don't think the connection is in my booth, I think it's off in the video guy's main lair on the other side of campus. I'm not a vidiot and don't exactly know everything that is going on the other side of that wall.

The Audi has been rebooted.

I'll try to test individual outputs one at a time.

Chris I think you have it right. My understanding is that the two DSP's share audio information back and forth and give or take whatever signal they need from the network. It's sort of a shared two part brain. We were having problems originally because the video guys installed the second DSP on switched power. Everything would work fine, then the video guys would turn off their rack and go home and my audio would go crazy because my DSP suddenly couldn't find it's friend. I think the only way to disconnect video from the system is to crawl in the back of a tiny rack and unplug inputs one at a time. I'll see what happens.

Not sure if this helps at all, but my video guy was complaining about lots of noise from my rack of Shure ULX-P receivers. When you unmute the Shures the noise goes up into like the 60db range. There is a single Senny 300 G2 in the rack and it sounds clean. We stopped using the Shures for video and the video guy brings over some AT 3000's instead which we just set up as needed and they sound clean. It all seams really odd that there is so much noise as those ULX-P's are good quality and cost more than the AT 3000's. The Shures were plugged into the same circuit that the GL2400 is currently plugged into.

Should I try running the board through a UPS to clean the power?

EDIT: Just thinking that the GL2400, the rack of ULX-P's, the Audia EXPI (A/D converter), a computer for running SFX, a set of powered booth monitor speakers, and a CD burner all are plugged into the same Tripp Lite surge supressor. The problem could easily be that the power just isn't clean on that circut. Right? They really should be running through a line conditioner shouldn't they? Would one good UPS clean the electricity enough to fix any problems?

Pluss I need to install all ETC Sensor Sinewave dimmers to make Derek happy.
 
Last edited:
Re: Noisy A&H GL2400

One of the areas that UTP is weak in is RF interference.

The best UPS to get is one that is smart power and is not a back up ups, but is an actual online continuous sine wave generated power

As I said before, just remember that video is typically an UNBALANCED system, So if you system and the video system share a common ground it is not unlike having an balanced and unbalanced audio system tied together

Are the Shure power connections two or three pin edisons?

Sounds like fun

Sharyn
 
Re: Noisy A&H GL2400

This sounds like a gain structure problem. If the inputs of the Audia are set for mic level, and being driven by line level outputs of the console, there will be excessive noise.

Are you having to keep the send levels set extremely low for the video feeds? If the levels don't show up within the range of the meters on the console, then the gain structure is the problem.

Actually it's the oposite we are driving them moderately high.

Here's one more piece in favor of grounding issues. I have a PC purchased from Stage Research setup for SFX. This sends signal out trhough an Echo Layla then to the GL2400. With the computer (and Layla) turned off and the computer input channel's silenced and muted. If you PFL the line that the computer comes in on, there is a low frequency hum. All other channels when PFL'ed produce a hiss when you get the head phones up around 80% or so.
 

Users who are viewing this thread

Back