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Hum in Avid Mojo audio signals
I have problems with a hum in both the line audio-outputs
and the headphones-output from an analogue Mojo connected
to a computer with Media Composer.
All signalcables are high quality and connected properly
and away from powercables and AC-adaptors etc.
The hum in the line audio-outputs sounds diffrent than the
hum in the headphones-output. Yes, it´s true!The hum starts as soon as the Mojo-logo is shown on
the reference-monitor.
And when the Mojo-logo goes to black for a few seconds,
while the system is loading, the hum is gone until the
Mojo-logo(or a videoclip) displays again on the reference-monitor.Can anyone help me to understand what’s wrong in the system?
Regards,
Roger
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2 Replies
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Hi Roger –
the most common cause of hum is from plugging equipment into different power outlets on your walls. It is VERY VERY COMMON to have grounding problems in places (especially in older city’s like Manhattan). I urge you to get some cheapo AC outlet strips, and plug EVERYTHING in your system into ONE WALL OUTLET – just for now, just until you identify where your hum is coming from. If you have Cable TV plugged into your system somewhere, (like a VHS machine) UNPLUG the cable feed from the wall, as this is another common source of grounding issues.If you say “I can’t plug everything into the same outlet because the breaker pops” – this is the start of the problem that you have (insufficient electricity for your system). Remember, you have not given much details, and this is my first guess as to what is going on here. You should post EXACTLY what you have in your entire system – is it a stand alone system, is it tied into a machine room, do you have a long video cable feeding a TV monitor into another room off of the Mojo, or a VTR in your system ?
99% of the time, audio hum problems come from electrical grounding issues, and not “old wives tales” like “lift the grounds on the audio cables on one side”, or “cross your audio wires with your AC power cords at 90 degree angles”. People always love making up stories (based on things they can resolve themselves, as opposed to having to ultimately hire an electrician to help solve these problems, which usually costs a lot of money).
Bob Zelin
Bob Zelin
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Hi Bob.
All components in the system is connected to the same
AC-outlet.
The two VGA-monitors and the reference-monitor(YUV) is
connected with 5 meter cables.
A VTR is connected to the Mojo with a 1 meter firewire-
cable, and there is an audiomonitor-system connected to
the line audio-outputs of the Mojo.
All signal-cables is kept away from the AC-powercables.Note that the hum only appears when the Avid Mojo-logo or a
videoclip is displayed on the reference-monitor.
When the Avid Mojo-logo goes to black for a few seconds, while the system is loading/working, there is no hum at all.
But as soon as the Avid Mojo-logo or a videoclip is
displayed again on the reference-monitor, the hum starts.
Perhaps the problem is related to the communication between
the PC (Media Composer 2.7) and the Mojo (analogue)?Roger Thorsell
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