Removing earth from a laptop PSU - how dangerous?

[c128]

I work quite a bit from home, and have recently started using a new KVM to use the same monitor, keyboard mouse, speakers and microphone with my home PC and my work laptop, switching between them as need be. I say "new KVM" as I had been using one without audio for years, but needed mic and speaker support for VOIP conferences and the like. Anyway...this isn't really a computer question, trust me .

Everything with the new KVM worked fine, apart from some awful hum, sizzling and crackling from the speakers. This was present with either my home PC or my work laptop active, but far worse with my work laptop selected. A bit of Googling threw up the laptop PSU being the problem. Sure enough, running off batteries and the hum/sizzle/crackle went away - totally with my home PC active, and almost completely with the laptop selected - not practical as a workaround, however, with a 2 hour battery life. Anyway, the suggested "fix" was to remove the earth from the PSU - rather than doing this, I've effectively done the same thing temporarily with some tape over the earth ping of the plug - all fine, at least from an audio, if not safety, point of view. Obviously the earth's there for a reason though...

What are the potential ongoing problem's with running things like this?

 

[Lectrician]

As you work from home, have you not got a UPS running? If so, plug the laptop into that rather than directly to the mains.

From a safety point of view? You no longer have an safety. You have removed the safety earth connection which is there to protect you, your laptop and your property.

 

[sm1thson]

I think you can get isolation transformers that go on the audio lines to avoid earth hum like this, I’m sure theres probably something more appropriate but I think I have seen ones aimed at car audio, you could put these on the audio line and it would isolate the earth there, but still passing the audio signal.

Laptop PSUS are a funny one in that the earth isn’t used to earth the outer (as its plastic) but is used for the filters within in. without it would break EMC regulations, I don’t know what other potential floors it would introduce.

 

[ninjacat]

Isolating transformers or DI boxes - cheap ones such as Behringer or more expensive - interspace industries - http://www.interspaceind.com/products/product.php?id=7 should work.

Another option will be an external sound card. Shouldn't remove earth for obvious safety reasons.

 

[c128]

In reply to the above...

UPS

No UPS - but that's a good point, as it's something I had been considering in the past but then totally forgot about. Not having really thought about how UPS' work in general, I guess you're effectively working off the charged battery all the time, but only solely when/if there's a power outage? If so, then do you mean that this effectively provides a barrier from direct mains earth hum etc? mmm...that sounds like a really good option, if so.

Mains Conditioners, Transformers etc.

Looking at past postings related to this, folk seem to have had limited success with mains conditioners and the like. I can't vouch for the thoroughness of their testing, but the only real results seem to have been through the use of removing the earth, some people also using ferrite chokes in conjunction.

External sound card.

Don't really want to go down this road. It's a work laptop and I'd like to use it "as is" as much as possible. Any non-standard spec hardware and drivers tends to get our IS department hot under the collar, and I feel this ought to be sortable elsewhere...

The other thing to say in all of this is that it's not so much the mains hum that's really the issue - I could live with that. With the earth connected it's more the crackling, hissing and "video to sound" issues you get e.g. hard-drive activity, scrolling a window etc. etc. all have a background sound of their own... I assume it's all related though?

 

[bernardgreen]

Not having really thought about how UPS' work in general, I guess you're effectively working off the charged battery all the time,

In a true UPS ( Un-interruptable Power Supply ) the load is powered by the battery via and invertor and the battery float charged by the mains. The UPS only cuts to mains if the invertor fails.

In an SPS ( Standby Power Supply ) the battery and invertor are only in use when the mains has failed.

For a laptop the UPS can be a battery of the correct voltage to feed DC to the laptop in place of the mains to DC power supply.

Removing the earth from a lap top supply is NOT a good idea.

 

[ninjacat]

Isolating transformers and DI boxes are different to mains conditioners and work on the audio signal not the mains feed to the laptop.

To be honest, if it is hard drive noise then an external card is the most likely fix. Speak to IT and bget them to provide it (Good luck)

 

[c128]

In a true UPS ( Un-interruptable Power Supply ) the load is powered by the battery via and invertor and the battery float charged by the mains. The UPS only cuts to mains if the invertor fails.

In an SPS ( Standby Power Supply ) the battery and invertor are only in use when the mains has failed.

Ahh, OK, thanks. So...am I safe-ish i assuming that a true UPS will solve my mains interference issues? Are most UPS that are described as UPS actually true UPS, if you get what I mean ?

 

[electronicsuk]

Most cheap UPSs are not double bypass/fully online/whichever term you prefer. An audio isolation transformer would be a better solution, and they are readiy available from electronics stores such as maplin.

 

[ban-all-sheds]

Never seen one with a DC output that will take the place of a laptop PSU.

That doesn't mean there aren't any, but I would have thought that there are so many different voltage requirements that it can't be an economic proposition to build UPSs with DC laptop outputs.

And if you use a UPS to supply your laptop power brick then it will do SFA to resolve a problem of EMI from it...

 

[Hughie]

I do a lot of presentations with embedded audio/video played from my laptop and the PSU noise you describe is a real pain.

As has already been suggested a DI box (Direct Injection - guitarists use them so obtainable from a music shop or specialists like Studiospares.com) is the easiest way to go - especially if you get a passive one which is basically just a transformer in a pretty box (as opposed to active which has electronic gubbins inside and needs a battery).
Note that DI boxes are usually mono so if the stereo is important to your work you will need to source a stereo one (used by keyboard players) or buy two mono ones which is possibly easier to get cables for.

DI boxes also have an "earth lift" (or "ground lift") switch which disconnects the earth connection between the input and output sides. This only affects the audio earth connection and is not to be confused with the mains earth. You just select the position which sounds best.
H

 

[c128]

As has already been suggested a DI box (Direct Injection - guitarists use them so obtainable from a music shop or specialists like Studiospares.com) is the easiest way to go - especially if you get a passive one which is basically just a transformer in a pretty box (as opposed to active which has electronic gubbins inside and needs a battery).

Thanks, I'll have a butchers.

There's one other thing I've realised that puts a spanner in the works (slightly) with an audio only solution... Without the earth connected to the laptop PSU, I also get a much cleaner video signal (it's a VGA KVM). Perhaps this doesn't arise with DVI KVM's, but both my old and new ones produced background wavyness to the display from the laptop (home PC always fine). Again, disconnect the earth and, along with annoying audio issues, the video is much clearer too.

 

[Steve]

I have a laptop that has an un-earthed fig8 mains connector on its PSU.

I also have a laptop that has an earthed IEC (similar) mains connector on its PSU.

 

[c128]

...an old thread of mine, but I've just noticed something.

The background noise has mostly gone. The only difference? Well, I fitted one of the filter sockets as "advertised" on this forum, and still available in my local B&Q:

//www.diynot.com/forums/viewtopic.php?t=180696

Now...I'd actually forgotten mostly about the noise (I guess I have learnt to live with it) - I certainly didn't buy this socket with it in mind. Nonetheless, everything is much quieter here now.

 

[ericmark]

The earth going to the switch mode power supply is there in the main to remove spikes on mains supply but unless you have a circuit diagram you can't be 100% this is all it does. However you can get replacement power supplies shows standard two pin 2.5 amp connector no earth. I used this one when my old one failed and it runs so much cooler that old one that came with laptop.

As to desk top I have not seen any power supplies without an earth connection but there are different specks this one gives "Ripple-noise:5A res max. for 230VAC" looking at other supplies from same firm some don't say what it is. But this is really a specialised subject and I am sure if you contact supplies or if you have a good IT department they can recommend or try other power supplies.

As you approach the power limit there is more chance of ripple on the supply and no switch mode can cope with sudden loads and most audio amps still use the old style power supplies because of that.

I was told at University that you could not use switch mode power supplies for things like side band transmitters but now I see these are being sold so it seems manufactures have found a way to get around the short comings of switch mode power supplies. So I will guess the better supplies come with a bigger price tag?

P.S. inserting a diode into the earth may help as done with boats these are common with boats to stop the one or two volts different between boat and shore earths from eating away at the boat. It would mean under normal conditions no current would flow in earth connection it would only flow under fault conditions. Although I would think the units will cost more than new power supply.

I take it you have already tried de-coupling capacitors in connection leads?