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USB Galvanic Isolation...

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DJ-Dulux View Drop Down
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    Posted: 21 May 2020 at 12:51pm
Been looking at getting something to avoid laptop noise getting onto the audio signal path. My system uses a unbalanced to balanced converter before the processor so I don't have any issues currently. But if I add in the USB cable to control the loudspeaker processor I get lots of digital garbage getting onto the signal path. Unplugging laptop PSU solves the issue so believe its a earth issue related to the power supply.
 
My new 12V rig also has a similar issue when running from the inverter, breaking any earth connection seem to resolve. Therefore thinking I will just isolate the USB mixer and soundcard from the laptop....
 
I have been looking at this:
 
 
Any feedback?
 
Thanks,

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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2020 at 1:47pm
Looks good.

I had a similar query when I supplied a phono isolator for a DJ. It fixed the problem until one week he plugged his laptop USB external video card into his karaoke monitor...he hadn't mentioned this as part of his setup. A simple galvanic isolator cured that, not quite what you've got but isolating the USB link at one end or the other will do the same thing. It's all about breaking the earth loop without leaving anything actually un-earthed, for obvious safety reasons.
K. Edwards Electronics Engineers

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studio45 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2020 at 2:07pm
Working with 12v systems, whenever I have a noise problem I fit a filter to the positive power line. If a fair bit of current is needed I use an LC filter, that's a mid-value low ESR electrolytic cap in parallel to ground followed by an inductor in series (a few tens of uH with an Ohm or two will do). If it's for something low powered I use an RC filter, that's a small, very low ESR polyester cap in parallel to ground followed by a low value resistor (up to 1uF/10r). The point is to keep HF/RF noise out of the power supply to audio circuits, and encourage it to flow to ground instead. High frequencies don't like going through inductors or resistors but will much more happily flow through capacitors. 
If it's a 50Hz mains hum, this won't work very well. But for the 100kHz+ hash from a switching power supply, it's pretty effective.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DJ-Dulux Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2020 at 2:59pm
Thanks for the replies, I only have an issue with noise when the laptop power is connected, at other times its acceptable (12V via inverter). I may well have a look at filters just to see if it helps lower the noise floor in general though.
 
Regards USB, I think this one is a better option, its High speed too so should deal with DJ sound cards running a few channels...
 
 
Cheers,

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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 2020 at 4:58pm
always better to stop any noise at source rather than try to filter it out later.
The laptop charger is obviously completing the earth loop so breaking it somewhere is all that's required. Note that earth loops are sometimes completed (made) by AC-coupling just as well as hard wiring.    
K. Edwards Electronics Engineers

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