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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => Pro AV Forum => Topic started by: Brent Venter on February 26, 2014, 06:44:06 AM

Title: Pop-Up Audio
Post by: Brent Venter on February 26, 2014, 06:44:06 AM
Hi Guys

I have a problem with a cable docking station in a boardroom where the audio has inherent buzz when the VGA and audio flylead is connected to the laptop. Most times it is the laptop power supply when plugged in that creates this issue, however this time it is not the case. We have tried different notebooks and flyleads etc.

Would a small isolation transformer near the docking station be a solution to "cure" this issue and if so how do I implement it?

Thanks for the help!
Title: Re: Pop-Up Audio
Post by: Brad Weber on February 26, 2014, 01:05:54 PM
Quote from: Brent Venter on February 26, 2014, 06:44:06 AM
I have a problem with a cable docking station in a boardroom where the audio has inherent buzz when the VGA and audio flylead is connected to the laptop. Most times it is the laptop power supply when plugged in that creates this issue, however this time it is not the case. We have tried different notebooks and flyleads etc.
So are you saying that the buzz occurs even if the laptop is run off its battery?  If so then that seems to eliminate it being a ground loop related to the AC power.

Do you get the buzz if you connect just the audio and not the VGA video?
Title: Re: Pop-Up Audio
Post by: Brent Venter on February 26, 2014, 01:11:13 PM
Quote from: Brad Weber on February 26, 2014, 01:05:54 PM
So are you saying that the buzz occurs even if the laptop is run off its battery?  If so then that seems to eliminate it being a ground loop related to the AC power.

Do you get the buzz if you connect just the audio and not the VGA video?

Hi Brad, yes when the VGA is connected it just exacerbates the problem when just the audio is connected. Maybe an issue where grounds are connected to the pop-up chassis?
Title: Re: Pop-Up Audio
Post by: g'bye, Dick Rees on February 26, 2014, 01:46:49 PM
Quote from: Brent Venter on February 26, 2014, 06:44:06 AM
Hi Guys

I have a problem with a cable docking station in a boardroom where the audio has inherent buzz when the VGA and audio flylead is connected to the laptop. Most times it is the laptop power supply when plugged in that creates this issue, however this time it is not the case. We have tried different notebooks and flyleads etc.

Would a small isolation transformer near the docking station be a solution to "cure" this issue and if so how do I implement it?

Thanks for the help!

What audio connection out of the laptop?
Title: Re: Pop-Up Audio
Post by: Brent Venter on February 26, 2014, 02:36:31 PM
Quote from: dick rees on February 26, 2014, 01:46:49 PM
What audio connection out of the laptop?

Unbalanced stereo on 1/8" TRS jack
Title: Re: Pop-Up Audio
Post by: g'bye, Dick Rees on February 27, 2014, 12:08:02 PM
Quote from: Brent Venter on February 26, 2014, 02:36:31 PM
Unbalanced stereo on 1/8" TRS jack

http://www.fullcompass.com/search.php?parent=471&search_simple=true&txtAll=Peavey+USB-p

This has solved all such problems for me.  Does not require any driver to be installed.  Windows XP has recognized it every time and I assum 7 and 8 will also.  On Mac you go to preferences and tick the box next to it to select it for your audio output.
Title: Re: Pop-Up Audio
Post by: Jerome Malsack on February 28, 2014, 01:08:39 PM
Still a ground loop and the laptop is the connection between the two.  Amp is grounded and projector is grounded.   They are seeing a difference.   Using isolation transformers on the two audio L/R should correct the problem.  When adding the laptop power you may still see ground loop as horizontal bars moving in the video.  Laptop power is in wall into one breaker and the power to the projector is on another breaker.  The cables have different lengths / corrosion / joints.