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yet another laptop noise problem - hdmi

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godathunder View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote godathunder Quote  Post ReplyReply Direct Link To This Post Topic: yet another laptop noise problem - hdmi
    Posted: 04 February 2019 at 12:56pm
mutter mutter shite switchmode psu noise crap mutter mutter

my problem is that my laptop is dumping its unwanted noises into my hifi

its the usual problem, fine on battery. fizzes, pops, hums and buzzes with the psu connected - present with all psus tried - disappears if I do the naughty thing with the earth disconnected (put your swords away gentlemen, it was done for test purposes only)

isolation transformers would be lovely but:

my problem is that Im connecting via hdmi

has anyone come across a hdmi isolation solution?

or I may just build a proper heavy metal psu and see if that improves matters


Edited by godathunder - 04 February 2019 at 12:58pm
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toastyghost View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 04 February 2019 at 1:00pm
Your laptop is double insulated anyways and doesn’t need an earth. If nobody else is gonna use it then remove away.
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godathunder View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote godathunder Quote  Post ReplyReply Direct Link To This Post Posted: 04 February 2019 at 1:03pm
point taken but it feels like the wrong solution

Im obviously looking for a way of further complicating my life
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efinque View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote efinque Quote  Post ReplyReply Direct Link To This Post Posted: 04 February 2019 at 1:15pm
At a venue I used to DJ and host karaoke there's a micro-USB to HDMI adapter via an Ethernet/RJ45 from a tablet to the main system which is used for the AV signal (the distance between the tablet and the booth is about 20m)

Sometimes the cable/adapter (which also supplies power to the tablet) gets loose which cuts the signal.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cravings Quote  Post ReplyReply Direct Link To This Post Posted: 04 February 2019 at 1:18pm
i'm sure that answers your question.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dylan-penguinmedia Quote  Post ReplyReply Direct Link To This Post Posted: 04 February 2019 at 1:20pm
Originally posted by cravings cravings wrote:

i'm sure that answers your question.

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godathunder View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote godathunder Quote  Post ReplyReply Direct Link To This Post Posted: 04 February 2019 at 1:21pm
Originally posted by efinque efinque wrote:

At a venue I used to DJ and host karaoke there's a micro-USB to HDMI adapter via an Ethernet/RJ45 from a tablet to the main system which is used for the AV signal (the distance between the tablet and the booth is about 20m)

Sometimes the cable/adapter (which also supplies power to the tablet) gets loose which cuts the signal.

thank you efinque, thats very kind of you but possibly not entirely pertinent to my problem
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efinque View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote efinque Quote  Post ReplyReply Direct Link To This Post Posted: 04 February 2019 at 1:28pm
Originally posted by godathunder godathunder wrote:

thank you efinque, thats very kind of you but possibly not entirely pertinent to my problem

External USB/Firewire interface if you're running sound only?

Laptop soundcards are horrible anyway.
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godathunder View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote godathunder Quote  Post ReplyReply Direct Link To This Post Posted: 04 February 2019 at 1:34pm
audio + video output required hence hdmi

Ive got a couple of those cheap little behringer usb interfaces for 2ch audio needs
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 04 February 2019 at 2:02pm
If the laptop adapter has an earth then it's there for a reason, it's using it to provide the barrier between mains and low voltage output. So don't remove it. A class 1 psu is also allowed to leak alot more current to earth than a class 2 psu and with the earth lifted that leakage is going to present itself on any exposed conductor on or connected to the laptop.

I would look around to see if there's a double insulated power supply option (these used enhanced pri-sec insulation), the sort that uses a figure-8 mains lead. It's no guarantee of being noise free but it's got to be worth a try, I know clients that have had success with it in karaoke with multiple TVs.

I'm sure you can get an HDMI isolator but I bet they're dear.



K. Edwards Electronics Engineers

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godathunder View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote godathunder Quote  Post ReplyReply Direct Link To This Post Posted: 04 February 2019 at 2:24pm
I think a rummage round the spares boxes is in order. Ill see if I can knock up a suitable 19v/70w wirewound psu out of the parts Ive got lying round and some minimal ordering. 

will be interesting to see if it provides a solution

Ill add it to the to do list and report back with results at some distant point
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kedwardsleisure View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 04 February 2019 at 2:54pm
that's going to be a hell of a linear power supply! It'll need to use a switching regulator to get that sort of current without a heatsink the size of a potato waffle
K. Edwards Electronics Engineers

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