SMPS and grounding

[sandyk]

 

Cornan

Silicon Chip magazine published an article on this in July 2006, complete with measurements from different DVD players, showing the HF rubbish on the AC residual from the SMPS, which could measure as high as half the A.C. Mains voltage.. They used a 3 pin mains plug with only the earth wire connected, and a capacitor to the equipment's metal case.

 Unfortunately, a HDD crash saw me lose my copy of the original article. However several members were sent copies of this and another connected article. several years ago

Attached is a link to a partial copy of the "Tingle Terminator" article.

Regards

Alex

Attached is a link to a copy of one of the pages that I somehow managed to retain.

https://imageshack.com/i/po722bNDj

 

http://archive.siliconchip.com.au/cms/A_107106/article.html

[sandyk]

Just now, Cornan said:

 

Thanks for the link Alex! However, I am not sure that this is totally tranferable to a floating SMPS that have both the negative DC output and chassis totally isolated from the safety ground while (quote) "they used a 3 pin mains plug with only the earth wire connected, and a capacitor to the equipment's metal case".

 

 

If you were able to read the original articles and see the measurements, you would see that it is.

Most CD/DVD/BR players use SMPS, and are double insulated with no connection to mains earth.(floating)

[sandyk]

The schematic at the link shows the mandatory culprits responsible for most of the problems.

 

http://imageshack.com/a/img923/6873/7NUrjX.jpg

 

 

[sandyk]

Cornan

 I just located a backup copy of the 2 original articles .

I will PM you the DL link. If J.S. is also interested , perhaps he can PM me for the link to the articles.

Alex

 

 

[sandyk]

15 minutes ago, Cornan said:

 

Thanks Alex! Here is how the Gophert csp-3205II looks like on the inside (borrowed picture):

 

 

I am no good with schematics. Are we talking about the same thing?

 

 

 

 In the schematic, you will see 2 capacitors highlighted in yellow.

They connect the mains side of the SMPS to the secondary side.

IIRC, they are mainly there to meet RF/EMI regulations.

 

Please check your PMs for a DL link to a copy of the 2 articles mentioned.

Do not repost the link, as it is copyright material.

[sandyk]

Hi John

 The safety, and potential damage aspect of inexperienced members doing what you are suggesting worries me a little. (and may also contravene FCC requirements ?)

 Perhaps a compromise of something like a series 10 ohm .25W resistor at the equipment end of the added earth wire may be a good compromise ,and still be quite effective ? The series resistor could be inside a small length of heat shrink.

 

 Regards

Alex

[sandyk]

Please check your PMs

 

Alex

[sandyk]

 Is this SMPS earthing really a problem generally, other than mainly with USB Audio where SMPS PSUs may be in use ?

I measure around 99V AC  from the "earth" side of the output sockets on a TEAC HDB 850 STB to mains earth.

 However, with Coax SPDIF connected from it to my DAC, which is connected to an earthed Class A Power amplifier, or HDMI plugged from it into my TV, which also has an Oppo 103 connected to it via HDMI, there is no leakage voltage measurable.

Could it be that adding an additional earth to the SMPS powered devices 0V rail, MAY in a situation such as this, where earthing is already likely to be optimal, result in some minor degradation ?

I also fail to see the need for a direct earth connection, when this leakage voltage is at a fairly high impedance, to use direct earthing which could possibly introduce a degree of earth loop if not carefully implemented, when a series low value resistor to earth (e.g. 10 or 22 ohms, or even higher) should have a similar effect ? 

Alex

[sandyk]

45 minutes ago, opus101 said:

There's the problem in a nutshell - the STB leakage current is now travelling through your DAC - in through the digital input and out again at analog outputs. Presumably from this, it doesn't have an input transformer. Once those noise currents are inside the DAC itself there's no telling what damage they're doing to your SQ.

 

Given that this DIY DAC readily outperformed a Bricasti M1, the damage would have to be quite minor. Unfortunately there is no room to install a Coax SPDIF transformer.

The "earth reference''  right through the chain, is via 10 ohm resistors to PCB "earth" at the L and R inputs  of the Class A Power Amplifier. Neither the DAC, or Preamp have their  0 volts lines connected to mains earth via the power supply either, and the Source switch in the Preamp only connects through the "earth" side of the selected Input.

 

[sandyk]

26 minutes ago, opus101 said:

Are the RCA socket outers on your poweramp wired direct to chassis (mains earth) or are they routed onto the PCB? If the latter then all your noise current runs through that 10ohm resistor.

 

 

No, the sockets are not grounded to chassis. They connect via the 10 ohm "EARTH LIFT " resistors on  the PCB , which is a well  accepted, and  common method of reducing earth loop problems.

[sandyk]

40 minutes ago, opus101 said:

you could put transformers externally on the analog outs (for example).

 

 

YUK !!!

 

Nobody in their right mind would do this to an amplifier with very close to 4 Zeroes in it's distortion measurements, and a high S/N ratio, along with a very good 3D presentation on good material.

[sandyk]

42 minutes ago, opus101 said:

'Ground lift' resistors date back to ye olde days when there was a strong likelihood the source component would present a low impedance to mains earth on its 0V and SMPSUs weren't as prevalent as they are nowadays.

 

Many designers still use earth lift resistors for their benefits.

Silicon Chip magazine for example, has published some of the lowest distortion designs, and they still use "earth lift" resistors . (Typically .0006% for their SC ULD3)

As far as "ye olde days" goes, that's exactly what using expensive transformers is when there are far better design alternatives these days.

Have you read any of the Power Amplifier Design Handbooks written by highly respected U.K. author Douglas Self, for example ?

 

P.S.

 My own DIY system is fully D.C. coupled from the DAC, through the Preamp, and the !5W/Ch. Class A Amplifier. 

[sandyk]

10 minutes ago, opus101 said:

Curious - what are the sonic benefits of having 3 zeroes in the distortion figure?

 It is a matter of record that some amplifiers such as some of the Halcro designs with even lower distortion figures are acclaimed for their 3D presentation.

 My own Class A amplifier has been nicknamed by friends as " The Holo Amp"(as in Holographic)

It uses a front end balancing scheme, that can be readily further refined by using 1 additional transistor..

The claimed improvement was verified by DIY Audio members.

http://www.diyaudio.com/forums/solid-state/133018-current-mirror-discussion-15.html

[sandyk]

23 minutes ago, opus101 said:

Back to an earlier question still outstanding - which DIY DAC are you using?

 

 I am using a highly modified version of a published design from Silicon Chip magazine.

 

Attached is a photo of my own Class A amplifier. The front end is powered via by a modified version of a John Linsley Hood designed PSU Add-on. ( http://users.tpg.com.au/gerskine/greg/default.htm  - See Power Supplies)

 Quite a few were also constructed by members of a U.K. based forum using PCBs designed by members.

 

BTW, this is now all well off topic, and will be removed by Alex C.

[sandyk]

Greg

 John will correct me on this if I am wrong, but HF noise from an SMPS would be coupled into the secondary side ( the other side of the HF transformer) via the obligatory low value, and high voltage, capacitors that are connected between primary and secondary to meet FCC RF/EMI standards. This would be a high impedance source.

Incidentally, I have been looking at the high voltage leakage from my DTV STB as it connects into my TV and main system.

It hovers around 100VAC from the STB chassis to mains earth, but when the STB is connected via HDMI to the TV it is reduced to Zero.

I have disconnected the STB's  Antenna and coax SPDIF leads to verify this.  The interesting thing is that with nothing else plugged into the TV except the HDMI plug , and even when the TV's  2 wire mains plug is removed from the mains socket, the leakage STILL remains at Zero volts !

This shunting obviously is a good thing , but I am at a loss to see how this can happen.

 

Alex

 

[sandyk]

1 hour ago, gstew said:

Also curious about your DTV STB & TV puzzle. My 1st thought are some high-ohm (50k-1M) resistors across the HDMI inputs to ground in the TV and that this is sufficient to dissipate the  high-impedance leakage in the resistors. 

 

Hi Greg

 I can't understand how this can happen where the TV is SMPS powered , and the 2 wire mains plug has been unplugged.

There shouldn't be ANY connection to mains earth at all.

 

Regards

Alex

 

 

[sandyk]

This morning, with a Teac  HDB850 STB working at 240V AC (approx.) I measured an average of 90V AC from the "earth" side of it's output jacks to Mains Earth with nothing else connected.

 With a 1 megohm "bleed resistor" connected from the "earth" side of it's output jacks to mains earth, it only dropped to an average of 50V AC, which is still way too high. 

 

Alex

[sandyk]

4 hours ago, JohnSwenson said:

well you have now found the high impedance and low impedance part of leakage current. The 1 Meg shunts the high impedance part but doesn't do much for the low impedance part.

 

John S.

 Hi John

 Back in 2006 Silicon Chip magazine did similar experiments , and their version used a 22nF 275VAC X2 capacitor connected from the case to earth via a separate mains plug. They called it a " Tingle Terminator" . In  a later issue (October 2007) they did a series of tests using both SMPS powered and transformer powered CD/DVD players, where they published scope shots of the waveforms across a 100 ohm resistor connected from case to earth, with and without, the "Tingle Terminator."

 

Regards

Alex

[sandyk]

The outers of the sockets aren't necessarily connected to a metal chassis.

This means that you may be able to connect the earthing as John described, to say an RCA plug , plugged into a not in use RCA socket , without a connection to the inner of the plug.

 

If you have a DVM you can check whether or not the outers of the sockets are connected to the metalwork. You may also need to scrape away the anodising around a mounting screw to get a good contact.

You often need to do this with cases used for DIY projects in order to give decent screening, and continuity of the screening between front, back, top and bottom, and side panels.

[sandyk]

2 hours ago, JohnSwenson said:

This CAN happen between components that are close together IF they are on different circuits and there is a long distance back to the panel.

 

Hi John

 In my case I have 2 different AC mains feeds along the wall behind my gear, which I need to use rather than a huge power board behind the gear.  I must admit though, that in my system I have no evidence of audible mains hum, but I have gone to a great deal of trouble to reduce the possibility of such problems.

BUT, mains hum is not the ONLY indicator of inadvertent ground loops is it ?

Correct earthing is of vital importance, especially with Computer Audio, and USB especially.

 

Kind Regards

Alex 

[sandyk]

I don't particularly like the idea of grounding the case/ 0 volts rail of SMPS gear that wasn't designed to be earthed.

I am more concerned about retaining the existing safety factor when using 230VAC.

 

 When I get the chance, and obtain a 3 pin mains plug, I will try what Silicon Chip magazine did, which was to connect a 100 ohm .25W resistor to earth, which reduced the leakage voltage to a much lower level for measurement purposes, then try connecting a 22nF capacitor across the 100 ohms to mop up HF rubbish like they did .

100 ohms will not be low enough to cause any earth loop problems, although in the majority of cases a direct connection to mains earth won't either, as John has already said.

 I also checked my Oppo 103 which is SMPS powered, but it uses a 3 pin mains plug, and has no measurable AC  voltage to mains earth from it's chassis..

The STB that I will be trying this on, is powered from a separate mains feed to my main gear, so the chance of a minor mains loop is a little higher than normal..

Alex

[sandyk]

I have an STB which is connected to my DAC via coax SPDIF , as well as via HDMI to my TV.

 I have been a little concerned that the HDMI connection to the TV is causing a shunting of all the STB's SMPS residuals by some unknown ( to me)  mechanism, especially since they are both using different mains feeds, with the possibility of a minor earth loop.

With my STB, I also have a +5V low noise Linear PSU to power the connected USB memory stick used for recording. It also uses a short modified USB cable with +5V disconnected at the STB end. This results in improved performance of recorded HD TV,  even in comparison with direct reception of the reduced bit rate .mp4 HD TV transmissions used locally.

As the STB is sitting on top of the PSU, and the PSU uses a 3 pin mains socket without the mains earth connected,  I was able to fit a banana socket to the PSU which I connected to mains earth. This enabled me to use a short connecting lead with a banana plug on one end, and an RCA plug with only the earth side connected, to connect mains earth to the 0 volts side of an unused RCA socket on the STB. 

This has resulted in a further quite noticeable improvement in Ambience and delineation of onscreen voices on many TV shows. 

As I am using a short pluggable lead, the improvement is readily verified, simply by connecting and disconnecting this additional mains earth wire.

 

Alex

 

[sandyk]

14 hours ago, Cornan said:

A isolation transformer, even one with floating secondary, have the safety ground intact. It is just the output that is not grounded to the secondary of the isolation transformer.

 

 

 It takes something like 50mA of A.C. to kill you.

That is unlikely to be noticed by an RCD on the Primary side when the output is far, far, greater than that amount of current ?

Just because the AC output is floating, doesn't mean that devices powered by it don't have any return path to earth.

Please correct me if my thinking in this area is incorrect.

One and a half is the resident expert in this area.

 

Alex 

[sandyk]

https://www.computeraudiophile.com/forums/topic/31877-iso-regen-listening-impressions-kicked-off-with-some-measurements/?page=32

 

[sandyk]

3 hours ago, Bricki said:

The other improvement was to remove my ethernet connection with my desktop computer and use WiFi instead. This means I no longer have a device on the network powered by a smps where the - dc output isn't grounded. All these tweaks added up to a significant improvement in sq ???

 

To overcome a similar problem, I used a "4 Way/Port Manual Sharing Switch Box Network Ethernet Selector Splitter Switcher " between the PC and the Broadband Modem.

 When ripping CDs and playing music I switched off the connection between the modem and the PC by just pushing a push button.