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

Im obviously looking for a way of further complicating my life

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

Ive got a couple of those cheap little behringer usb interfaces for 2ch audio needs

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

Fully sorted 

Maybe the noise won't be present on the USB sockets...

The thought was the combined 0V rail MAY have an impact on the noise (in a good way) as they will all be steming from the same place on the USB output.

As you say... stranger things!

...to add, maybe a USB powered hub would isolate the laptops rails and then plug in a USB to HDMI adaptor... I know we are getting into the realms of silliness at this point but it saves removing the earth bond of the PSU or anything daft

really? it seemed fairly sensibly sized to me - 

Ive probably got a big enough 230-20ish v tx and rectifier etc somewhere

would I be able to parallel a pair of these to regulate it?

https://ie.rs-online.com/web/p/linear-voltage-regulators/8056521/" rel="nofollow - https://ie.rs-online.com/web/p/linear-voltage-regulators/8056521/ (I know theyre only 18v)

mounted on

https://ie.rs-online.com/web/p/heatsinks/1898555/" rel="nofollow - https://ie.rs-online.com/web/p/heatsinks/1898555/

watcha think?

edit: apparently paralleling regulators is not quite as easy as hoped

Conceptually, there's switching noise present on the audio because somehow, the path to ground via the HDMI has a lower RF impedance than the neutral connection of the power supply. Why that should be I couldn't say, but that will be the mechanics of what's happening. It all ought to be decoupled in the supply circuitry, but perhaps some caps are either missing or defunct? 

Can you add a real earth connection - put on a 3-pin plug, add a green/yellow wire - and tie it to the power supply output's 0v side? Unsure of the safety implications of that, but it should ensure that the lowest impedance path for noise is not through the HDMI grounds any more!

But select the output audio device as headphones. Use regular line cable and ground lift as appropriate? 

Not really helping you solve the problem, but maybe working around it? 

I suspect that heatsink is not up to the job, you need to work out the power being dissipated by the regulators pass element, to do this you need to know what voltage the regulator pass element is dropping and then multiply that by the maximum current it’s going to pass... then multiplying the calculated power by 2.3 (the heatsink in the link is 2.3°k\watt) to give you the temperature rise (in° kelvin) above the ambient temperature.

Is it possible for you to use a USB to HDMI converter for your video and sound, I ask as you can get a USB galvanic isolator?

https://uk.farnell.com/olimex/usb-iso/usb-isolator-1000vdc-for-pc-laptop/dp/1795095" rel="nofollow - https://uk.farnell.com/olimex/usb-iso/usb-isolator-1000vdc-for-pc-laptop/dp/1795095

The one in the link above is USB2, I have seen USB3 ones for about £70.00

unfortunately, as I look at the cost and rather pointless complexity and added points of failure of putting hdmi-usb-isolator-usb-hdmi in the signal path I wonder why Im bothering when I know at heart that toasty nailed it in the 1st post.

if this was being installed somewhere where joe public or dj dave was being put at risk it would be worth the added cost etc but this is for my use only (well, and the kids, but I dont like them). I know the electrical install its being powered from is fine, has a nice low zs and suitably protected (I wired it). the hifi has its own dedicated circuit but the noise persists whether the laptop is powered from this, or an adjacent circuit

it annoys me to do it but I think that cutting off the mains plug and rewiring sans cpc is the best current option though building a linear psu will remain on the project list for the coming months

I think it just galls me that this seems to be such a common problem due to acceptance of cheap and shitty psu design in consumer goods

When I had my repair business I regularly had mixing decks in with input channels blown due to the DJ removing the laptop psu ground to solve this issue then plugging the laptop into the grounded mixer!!  

As Kevin correctly pointed out the problem with class 1 psu is that they have a higher leakage current than the non-earthed class 2 supplies (3.5mA leakage for class 1 IT equipment, 0.25mA for class 2), and when the earth is disconnected the output from the PSU sits with 115-120Volts leakage on the output (although at low current: @ up-to 3.5mA), when the laptop is then plugged into a grounded piece of equipment the 115-120Volt leakage is then dissipated to ground via the equipment often frying it in the process.    

I see your point

do you feel studio45s suggestion of running a bond to the laptop/psu 0v rail is a sensible one?

I assume that it isnt done because my laptop would no longer be a class 2 device which no doubt has ramifications in compliance

studio45 wrote: Can you add a real earth connection - put on a 3-pin plug, add a green/yellow wire - and tie it to the power supply output's 0v side? Unsure of the safety implications of that, but it should ensure that the lowest impedance path for noise is not through the HDMI grounds any more!

I removed the earth in the XLR connections and that cut it out but now use a usb sound card as well now nothing spectacular but it does the job 

But then, it did only cost £13 delivered, as opposed to £90+ for a real Apple unit. I was about to add a ground wire to it, then it died completely, so I just got another one, and that doesn't do it at all!

This.

laptop direct to tv (class 2) via hdmi

tv to decoder via optical

nasty noises has done goned

still passes 5.1 audio in most formats Im likely to need although Im not going to be able to pass the higher resolution formats (not that makes a lot of difference given the state of my hearing) 

btw, on the subject of higher res formats, does anyone know of a dirt cheap hdmi extractor decodes dsd to dolby digital or similar? 

I picked one of these up which suggests dsd compatibility but doesnt seem to support it in practice

https://www.amazon.co.uk/dp/B07D7M8LDN/ref=pe_3187911_189395841_TE_dp_1" rel="nofollow - https://www.amazon.co.uk/dp/B07D7M8LDN/ref=pe_3187911_189395841_TE_dp_1