Great video here on how to break 'ground loops' which is what causes noise/hum on amplified speakers or PA equipment connected to a Laptop PC.
Curing Laptop Noise and Ground Loop Audio Interference - YouTube
This is something which has plagued me for years, I always knew it was a ground loop causing it, but I never knew the cure was as simple as changing the type of powersupply you're using on the laptop, obvious when you've watched the video.
Last edited by Dos_Box; 21st August 2012 at 10:39 AM.
I spotted that a while ago, more by accident than research. We have several identical laptops we use for presentations, consistently one was quiet, and then I realised it had a two pin mains lead. That said I am very tempted by the Hd400 to silence the buzz from visiting speakers laptops, where we can't change the PSU.
Or you could just buy a ground loop isolator from amazon.
They are about 6 quid. We bought one and works a treat.
I had a decent one we used in the hall on the large PA setup, but that was about £30 and needed a battery to work, it did a great job thou.
Last edited by maniac; 14th August 2012 at 10:37 PM.
We use the ones that look like an oversized cotton reel with a short length of cable and male/female phono connections. We supply them with installations and use them on our hire fleet. They work a treat.
Well if they don't fit the bill you really need to go for a full DI box with a ground lifting function. They are not too expensive, but the connections tend to be XLR or 1/4" jack, which brings its own set of problems when you're using phono cables! It also pays, especially if you've got longer cable runs, (ie, anything over a couple of meters) to use a good quality phono cable.
We've known about the double insulated power supply fix for some time now, unfortunately, they are becoming more difficult to come by. It also cures the wavy line effect that we get on some projectors using earthed power supplies.
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