Promethean Direct Support Thread, speaker hum on the ABV378PRO in Direct Support; Hi
Recently we got some ABV378PRO boards installed. Audio gets to the board in two ways: via USB with the ...
18th December 2013, 01:58 PM #1
speaker hum on the ABV378PRO
Recently we got some ABV378PRO boards installed. Audio gets to the board in two ways: via USB with the Activdriver, and also through HDMI: Sound is carried via HDMI to the projector, and then there is a jack to jack cable 3.5mm from the audio out on the projector which goes into one of the inputs on the side of the Activboard.
The problem is, when both cables are plugged in together, we get a loud hum from the speakers. It is worse on some boards than others. Remove either cable (usb from the laptop, or 3.5mm jack from the side board) and the hum stops.
My question is, is it possible to disable audio through the activdriver so that it isn't sent to the board? We don't need this because we have HDMI. And we want to keep the HDMI in case someone wants to use a different HDMI device with audio.
At the moment, it means that we pull the 3.5mm jack out and only plug it in when we need HDMI from another source.
Any help / advice would be appreciated.
19th December 2013, 10:24 AM #2
The information below is based on an assumption that you are using a Windows 7 machine
When the USB for the ActivBoard is connected you will find "Promethean USB Audio" listed as a playback device in the "playback" tab of the "Sounds" setting contained in the Windows Control Panel. Alternatively you could right click on the sound icon in the system tray and click "Playback devices", you can then right click on "Promethean USB Audio" and disable the device.
This MAY NOT solve the issue you are having with the humming speakers, as the issue could be being caused by an ineffective ground somewhere on the system/ setup.
There are a lot of questions to ask when starting to look at potential grounding issues and I will list some of them below:
1. What kind of system has been installed in the school? Is there a metal framework installed behind the board that has various audio and video connections on the side?
2. When you have the 3.5mm jack cable connected to the amplifier on the board, is this connected directly? If so which port is it connected to?
3. Do you still have the "hum" sound when the projector is in stand-by?
4. If you are using a laptop, does the "hum" stop when you remove the PSU for the laptop?
5. If you connect all mains powered devices connected to the PC (including the PC) from the same socket (using an extension socket) does the hum vanish?
That should be enough to get us started
19th December 2013, 10:53 AM #3
yes it is a windows 7 laptop. I am on that site tomorrow so I'll go over what you have said and report back
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