SMPS and grounding

[sandyk]

56 minutes ago, Cornan said:

 

Nice one Alex!  I did´nt even know they existed. Do you mean that this "4 Way/Port Manual Sharing Switch Box Network Ethernet Selector Splitter Switcher " completely cut the ports (the magnetic boxes inside the switch) of choise? Do you have a link where to find them?

 

They just use multipole push button switches inside to disconnect the inputs not in use.

 When posting this I found the image associated with my original ebay purchase, but could no longer find this particular one on ebay. It also uses an additional short cable to the PC from it's output.

[sandyk]

6 minutes ago, Em2016 said:

Thanks John. I guess the challenge now is how to shunt the high impedance components from a computer's non-grounded SMPS, before it gets to the Intona/ISO REGEN etc.

 

 

Many Desktop PC's do have their SMPS grounded.

[sandyk]

34 minutes ago, Superdad said:

Since you seem to just now be joining this thread, I suggest you scroll back and read John's long treatise on the issues of leakage:

 Alex C

 Best to put this member on your Ignore list along with the usual disruptive types who like to crap in Audiophile threads in general, even where the poster is as  highly qualified and experienced as John is !

 

[sandyk]

2 hours ago, R1200CL said:

Could we hope for a 12VDC version to all the people now buying 12 V switches ?

 

From a different Alex.

The answer is likely to be no, due mainly to the low voltage ratings of Ultracaps.

You would need more of them in series in  each parallel group meaning that the PCB would need to be considerably larger as well.

This would also mean that a larger case would be required.

 

SandyK

 

[sandyk]

4 minutes ago, austinpop said:

However, that 15 ohm series resistance still bothers me. I'm hoping someone can validate that on their Groundhog, and explain why it's preferred to a straight wire (no resistance) like in John's gizmos.

 

Perhaps the resistance value is low enough to completely remove the high impedance sourced residual noise as measured from a typical SMPS, but high enough to reduce the possibility of inadvertent earth loops causing very low level hum where you may need to use 2 different mains outlets ?

[sandyk]

11 minutes ago, austinpop said:

That's certainly plausible, and did occur to me too.

 

But is it preferred?

 

 Good question.

I doubt that you would be able to measure or hear any difference between both methods.

 It always worries me a little about directly grounding the 0 volts rail of SMPS powered devices that were not designed to do this. Way back in 2006,  Silicon Chip magazine used a 22nF 275VAC X2 capacitor to mains earth instead, to help overcome this problem. ("Tingle Terminator") They connected a 100 ohm resistor across it for measurement purposes. However, despite my concerns, I did connect a direct earth to the 0 volts of my STB which has a Coax SPDIF connection into my DAC with improved results.

It was easier to implement.

[sandyk]

I posted the attached link to Voltage Regulator noise in another thread, but perhaps a few of you may find it interesting ?

 Alex

 

http://www.tnt-audio.com/clinica/regulators_noise1_e.html

[sandyk]

8 minutes ago, Superdad said:

What I have yet to see is the infamous "high impedance" noise.

 

 Hi Jesus

 With devices such as DVD players, STBs etc.,  all you need to do is check the A.C. voltage between the case/ 0 volts line and Mains Earth with a DMM.

This high impedance noise can  read as high as half the actual A.C. mains voltage.

It is mainly due to the obligatory low value, high voltage capacitor between the Primary and Secondary sides of cheaper SMPS

as used in many consumer items in order to meet FCC requirements.

 

Regards

Alex K.

[sandyk]

13 hours ago, wakka992 said:

can't you just solder a wire to the ground of a RCA plug? assuming you've plug laying around...

same for 3.5mm jack I assume

 

 I did that for my Teac STB which is connected to my DAC via Coax SPDIF, for a small but worthwhile audible improvement.

Just plug it into an unused RCA socket ./

[sandyk]

13 minutes ago, Cornan said:

This means that you use shielded USB cables right?

 

 

I have found that not all longer USB cables even have a shield, possibly to reduce capacitance so that they will even work at the longer length ?

 

Incidentally, USB connected Mouse and keyboard cables can also radiate quite a bit of RF/EMI that may affect DTV reception where an indoor aerial is not too far from the computer.

I have some clamp on 5mm inside diameter ferrite cores on order to try and alleviate this problem.

[sandyk]

Just now, Cornan said:

Like with ethernet cables USB cables clearly sounds best with a floating shield a la JSSG IMO. The problem occurs if the shield is connected to the plugs. 

 

 That would depend on the computer itself, with a possible benefit, as in my case, if the shield is connected at the PC end ONLY  with a Desktop computer which is earthed, as mine is.

I would only use ferrites on items such as Mouse and Keyboard leads.

[sandyk]

James

 Did you sort out your screw terminal type plug problem ?

 I noticed in a more recent post that a larger photo of the screw terminal plug showed + and - markings.

These markings were not visible with the small Jaycar photos.

 

Alex

[sandyk]

35 minutes ago, jamesg11 said:

Not that there aren’t things to bother about - a tweaker friend, who I tuned into the js grounding idea & who ordered some of the plugs etc for such, was told by an electrical engineer that the tweak was ‘illegal’ in Oz.

 Hi James

 I am not surprised and have previously suggested as much.

 That's another reason I originally suggested the Silicon Chip solution of a 22nF 275VAC X2 capacitor to earth instead, perhaps with a 100 ohm (or a little lower value resistor) 0.25W resistor in parallel. Using a 0.25W resistor should prevent any possible (highly unlikely!) damage scenario to the owner as well, by going open circuit under an unusual fault condition.

As the leakage is from a high impedance source, even a 100 ohm resistor to earth would reduce the original half mains voltage reading to most likely under 100mV.

 Perhaps Silicon Chip were aware of the illegalities of a direct earth connection in Australia at least, and why they said to remove evidence of  the bolted on solution before requesting a service  ?

 

Regards

Alex

[sandyk]

36 minutes ago, One and a half said:

 

Go for it. <=24Vdc is Extra Low Voltage, do what you like, no licensing required.

 

 Who is to know anyway ?

Despite my misgivings, I did connect a direct earth to the case of my Teac STB for an improved performance.

[sandyk]

I would have thought that the 2 parallel braided shields would already have a very low inductance, so I am surprised that connecting a single strand heavy gauge wire in parallel with both of them would make any noticeable difference.

 I will need to take John Swenson''s word on this. 

[sandyk]

11 hours ago, jamesg11 said:

Well, nanny state is not a concept honoured by me. But ... if our place burns down, the insurance companies will find plenty in my audio gear to justify a knock back on any claims ...

 

We need to remember here, that 50HZ 240VAC is way more lethal than the half that voltage used by our American cousins.

Have you ever been on the end of a nasty 240V shock ? I have when I was younger, and couldn't even tell a worried child that I was O.K. for almost a minute.

240VAC  can even throw you across a room !

[sandyk]

12 minutes ago, mansr said:

How can I tell if they were nasty or just normal 240V shocks?

 

 It depends on how well grounded you are ?

Somebody of your experience shouldn't need to ask a question like this.

Try making contact with 240VAC , first when wearing rubber boots, then with bare feet and report back to the forum if you are still able to !

P.S.

 I have also had mild 240VAC shocks due to moisture ingress into a bathroom light switch.

Taking appropriate precautions, although not being qualified as an electrician, I replaced the switch and  put some sleeving over the wires to it for the protection of other family members. 

[sandyk]

10 minutes ago, Cornan said:

A simple 2-pole RCD/GFCI at the output will do to protect them for possible dangers.

 

Even they need to be periodically tested. Have you tested all yours recently, or just assumed that they are working correctly ?

Statistics show that in 230VAC (nominal)  countries, that qualified electricians who have training in this area, are quite often electrocuted, possibly due to complacency ?

[sandyk]

17 minutes ago, One and a half said:

Ahem. Earthing 0V supplies on systems that are designed for 5V, has nothing to do with 230V systems. 

 

 What  if we have a breakdown between Primary and Secondary sides of a 5V SMPS supply ?

Are they completely immune to such things due to their design ?

Just asking.

[sandyk]

Just now, One and a half said:

If there's a complete breakdown,  then the 0V being earthed will blow a fuse or breaker and the downstream circuit is wrecked.  

 

 That is my main concern about using a direct earth instead of something like a low value 0.25W resistor (e.g.22 ohms or a little higher) which would very quickly go o/c and hopefully protect the downstream circuit.

A resistor of that value should be just as effective as a direct earth given the very high impedance leakage source.

[sandyk]

1 hour ago, rickca said:

I'm in a rental condo so I can't do the usual whole home thing.

 

 Use Power Boards with VDR's in them. They are cheap enough, and should give you quite a bit of protection.

[sandyk]

22 minutes ago, One and a half said:

A Topaz/Elgar/Xantech isolation transformer will to a better job and a VDR leaks (JS quote).

 

 We can't always do what we would like to do in this area,. when renting.

The leakage of a VDR may be insignificant compared with transformer efficiency losses ?

[sandyk]

Just now, rickca said:

If you're talking about MOV surge suppressors ... that's what the APC C5 is that gave me the whole problem in the first case!

 

 It seems likely that there may be a little more to it than just the use of  MOV/VDRs in the APC C5. 

Are you sure that it wasn't faulty due to previous high voltage spikes/surges ?

[sandyk]

33 minutes ago, One and a half said:

A 'large' isolation transformer can be hidden behind the equipment rack, about the size of a shoebox. 

Two of them would create a great base for a turntable,  they can weigh up to 30kg. Kinda ugly but functional.

 Garry

 In a Rental situation you will need to conceal such items, as Real Estate and Owner regular inspections are extremely unlikely to sanction any alterations whatsoever with the A.C. mains supplies, and will order you to remove them, no matter how safe they are, for Insurance reasons.

Incidentally, I don't normally connect VDRs from Active to Earth, only between Active and Neutral, as in a previous older house, even the typical high voltage capacitors used in filters to earth, occasionally helped to trip the ELCB.

Alex

[sandyk]

1 hour ago, rickca said:

Question is what kind of fault would give me this problem with a SMPS with -ve output grounded?  How could it affect other outlets on the same circuit? 

 

That's a bloody good question  !

 Perhaps Garry can answer that one ?