SMPS and grounding

[JohnSwenson]

Over the last month I have been performing extensive tests on leakage currents coming from SMPS power supplies. One of the most important results from this investigations is the makeup of this leakage current.

 

Previously my understanding was that leakage current was mainly a low frequency phenoninum, 60Hz, and its harmonics (60, 120, 180, 240 etc). My early investigations seemed to show that this was true with some high frequency components from the switching operation, but that this was fairly small in comparison to the whole. This turned out to be not true. It turns out that SMPS leakage is very hard to measure, it consists of some VERY high impedance components, on the order of 300 Mega ohms and some much lower impedance components.

 

None of the standard electronics test equipment will properly measure this, there impedance is simply too low and drastically changes the signal while trying to measure it. My only option was to build my own ultra high impedance differential probe (around 10 Giga ohms) so I can measure leakage current directly (rather than its affect on other equipment).

 

Because of this ultra high impedance it turns out leakage current can go all kinds of places you don't think about. It turns out to be extremely difficult to block using normal techniques, the blocking device has to have over a giga ohm to significantly attenuate it, this is VERY tough to achieve.

 

It turns out the best way to deal with this high impedance part is to shunt it around the audio equipment, there is a very easy way to do this, ground the negative output of the SMPS. It seems that even SMPS that include a ground pin don't actually use it for anything. This sounds too simple, but it actually works. PLEASE do not under any circumstances  attempt to modify an SMPS to do this, this is DEADLY, DO NOT attempt!!!

 

Fortunately there is a real easy - inexpensive way to do this, it doesn't take any complex knowledge, I'm calling this the power supply grounding adapter, here are a couple pictures:

 

 

This consists of three items and some wire. The yellow item is a three pin AC power plug (shown is the US model), the black parts are male and female DC barrel connectors with screw connectors, no soldering necessary! Amazon has a whole bunch of places selling these for CCTV cameras. The spec is 5.5mm outside and 2.1mm inside. Most you will see will be this spec. The + of the male is wired to the + of the female and - on the male goes to - of the female. Look at the close up picture, in order for the wire to go straight across one of the connectors has to be upside down. This is extremely important to get right. You can use many different types of wire for this, I used solid core 14AWG wire with the insulation stripped off.

 

A green wire goes from the ground pin of the AC plug to the - pin of one of the connectors, strip a little off and just stick it in with the wire going between the two connectors, use a screwdriver to tighten the screws, you are done.

 

The green wire does NOT have to be a heavy duty high power wire. The SMPS are already designed to be double insulated so the AC cannot show up on the DC output, grounding it does not pose any electrical threat. I just used some nice silicon rubber wire I bought on Amazon, but really any green wire will do.

 

You plug the output of the SMPS into the "jack" side, and the "plug" side goes into where you would have plugged the SMPS. The AC plug goes into the SAME power strip or duplex outlet where you plugged in the SMPS. This is very important to properly shunt the high impedance part of the leakage current. If it goes into a different circuit you can wind up making it worse.

 

You should do this on every SMPS that is somehow electrically connected into your sound system. Some items may have different connectors such and Ethernet switches etc. There are a bunch of different adapters available that can convert the 5.5/2.1 to just about anything out there, you may need to use a pair of these.

 

You may ask "how effective IS this?"

 

Here are some graphs, the first is the leakage current of an SMPS, the second is with this adapter plugged in:

 

 

 

That is a significant reduction in leakage for a $10 shunt adapter.

 

If you want to get it all you will have to use something like the LPS-1 which will get rid of it all.

 

Have fun,

 

John S.

 

[JohnSwenson]

1 hour ago, Cornan said:

 

Great write-up John! ?

How about when you are using a floating SMPS, where the safety ground is not connected to the negative output or chassis? I pretty much use these everywhere with truly great results. Especially effective powering network devices.

It turns out the floating ones are the worst, the leakage current has nowhere to go except what it is powering. None of the SMPS I have connect the DC output to safety ground so all these tests were done with floating SMPS (I actually have over a hundred tests), grounding really does dramatically reduce leakage from these devices into what they power.

 

John S.

[JohnSwenson]

3 hours ago, rickca said:

This is awesome, John!  It's going to be interesting to hear the impact of using this grounding adapter on things like routers/switches vs using a linear power supply.  Could I even do this with my powered studio monitors?

Every test I have done shows that grounding the DC output from a SMPS significantly reduces leakage current.

 

I have been doing other tests on networks and leakage, I will be making a post on that in a few days (probably in the thread on the Sonore forum).

 

John S.

[JohnSwenson]

3 hours ago, mike eastman said:

John,  can you connect more than one of the adaptors to the same plug ? Any reason you couldn't eliminate the plug and connect the wire direct to ground wire in receptacle box?

Yes you could ground more than one SMPS from the same wire, just remember that the ground needs to come from the same circuit, preferably the same power strip/outlet box as the SMPS. So say you have two SMPS plugged into the same strip, then yes grounding them from the same wire is fine.

 

You COULD ground an SMPS from a wire connected to ta metal box IF that box is known to be grounded. I'm not going to be responsible for people taking outlet boxes apart to get to a ground wire.

 

John S.

[JohnSwenson]

Remember the leakage from an SMPS contains both high impedance and low impedance components, the ground shunt gets rid of the high impedance components. The low impedance components are still left. These components are usually still greater in amplitude than many linears, but some linears might be a bit more.

 

BUT since what is left is the low impedance components, they CAN easily be blocked.

 

You can do the same thing with linears, which gets rid of THEIR high impedance components, just leaving the low impedance components, which are REALLY low.

 

I'm putting together another post in the next few days that shows how this works with network systems (I'll post that in the thread on the Sonore forum).

 

John S.

[JohnSwenson]

There are some ways to make this grounding easier to do for different size connectors, I will be making a post on this probably tomorrow night, stay tuned!

 

John S.

[JohnSwenson]

I've been experimenting with some ways to make the SMPS a little easier or applicable to a broader range of equipment. First off is a way to use it with equipment that does not have a 5.5x2.1 barrel jack.

 

I found another I had on hand, in this case the 7.5V Mean Well, this was exactly the voltage my switch took, IT plugs into the adapter, then a 5.5x2.1 to something else is used to plug into the device. In this case it was one of the adapters that came with the iPower. This works great. Using this technique I was able to ground the power to a bunch of different devices that had different plug sizes.

 

Both Amazon and Ebay have kits of these adapters available which include many different plug types.

 

Next up is an interesting kit from iFi called the Groundhog. It has a gounding system and several adapters to ground equipment in various ways. The one most appropriate is this:

 

This kit is unusual, it contains an IEC SOCKET, not a plug, you plug in a standard IEC power cord for your country. Most of you will already have several of these in your cable drawer. It doesn't matter what the country is, the IEC end is the same so they will plug right into the Groundhog. They call the adapter I show plugged in the "DC Spade", it is actually a little clip designed to clip onto the barrel of a 5.5 plug, thus grounding it. Clip it onto the barrel, then just plug it in.

 

This replaces the adapter shown in the first post with an off the shelf system you can buy, you don't have to build anything yourself. It is not dirt cheap, ($49), but for those that don't want to deal with building the adapter it is a nice alternative. It does exactly the same thing - it grounds the negative DC output of a power supply.

 

I hope this makes it a bit easier for people to try this approach.

 

John S.

[JohnSwenson]

On 9/23/2017 at 10:45 PM, tims said:

Appreciate it someone could explain what the effects these leakage currents have on different components and how they affect SQ. There's been a lot written about them recently but I'm still unclear about what they are and why we should minimiize them.

A link to another post explaining more would be fine.

 

Thanks.

Hi tims,

I've covered this in many of my other posts, I'll try and distill it down.

 

Leakage currents are caused by some of the voltage from the AC line "leaking" into the DC output of a power supply. In the good old days this was caused by capacitance in the transformer in the PS, thus it was power line related, 60Hz - 120Hz -180Hz, etc. With the advent of SMPS supplies it has gotten WAY more complicated. In addition to the traditional line related frequencies there is a LOT of other frequencies related to the switching of the supply. These cover a broad range of frequencies and can go up into the MHz range.

 

The traditional leakage current (what you will find talked about if you search the web) is from the DC output of the supply to earth ground (the third pin on the power plug, "safety ground"). Since a lot of equipment today does not have a safety ground pin, you would think leakage current is not a problem anymore, but it turns out there is another path for leakage current: from the output of one power supply, through interconnects between boxes and through the other boxes power supply and back through the AC line, forming a loop. I call these "leakage loops".

 

Now leakage is kind of difficult to understand. We are used to thinking of "power supply noise" as being between the negative and positive wires of the supply. BUT leakage affects both - and + exactly the SAME thus there is no differential noise between - and +. Both - and + move up and down together , this is called "common mode" noise. Noise filters, regulators etc are ALL designed to work on the differential noise between - and + they don't touch the common mode leakage.

 

So what does leakage current DO? It travels from one box to another through the cables connecting them. This current primarily flows through the "shield" of the cable and induces a small voltage across the shield, this gets seen by the subsequent devices and winds up on the output going to the speakers. We have ALWAYS had leakage currents in any system that is AC powered, but recently these effects have been much larger than in years gone by.

 

In digital audio systems the fact that computers are almost always powered by SMPS has been a major change. Since the SMPS almost always have much more leakage than linear supplies we now have MUCH more leakage current going into the rest of our systems.

 

In addition there also seems to be a different kind of interaction going on with digital systems. For preamps, power amps etc the leakage just winds up as very low level, mostly low frequency noise on the output. BUT when this leakage current goes through a DAC it can modulate the clock in the DAC constantly slightly changing its frequency, this causes increased jitter on the clock, which causes distortion of the output waveform, which is very different from just adding low level noise.

 

In any given system there can be multiple sources of leakage current different places where it goes. Every system is going to be different in this regard, making it impossible to say "do this and you will have zero leakage".

 

I hope this helps.

 

John S.

[JohnSwenson]

1 hour ago, Forehaven said:

ok, i give up.   what the hell is the dc adapter with pin outs??

Read the very first post in this thread. This covers how to build a grounding power adapter which grounds the negative wire coming from the DC output of an SMPS.

 

This adapter will only work if the existing connector is a 5.5x2.1 plug (many are).

 

The linked post covers a way to do this for a plug that is not 5.5x2.1.   In addition it covers a commercially available product that lets you do this grounding without having to build anything yourself.

 

John S.

 

 

[JohnSwenson]

On 10/1/2017 at 8:57 AM, gstew said:

John,

I don't understand the context & meaning of 'high impedance and low impedance components' of the SMPS noise.

 

I've never heard of noise having an impedance.

 

Can you provide some background and definition on that?

 

TIA!

 

Greg in Mississippi

Any electrical signal (useful or noise) has a "source impedance". You can think of this as a resistor the signal has to go through before it gets to where you are looking at it. It is an impedance because it can vary with frequency.

 

As a concrete example, lets say your source has an impedance of 1k ohms, if you apply that to a 1k ohm resistor to ground, the signal level will be cut in half. That is actually how you usually measure output impedance, run the input through a known resistance to ground and measure the level across the resistor, the output impedance acts as a voltage divider with the known resistor, from the resulting voltage you can calculate the source impedance.

 

For any given "noise source" there is at least one mechanism generating that noise. The mechanism will have a particular impedance associated with it. In many cases more than one mechanism is involved with generating noise, each of these mechanisms may have a different output impedance. There may also be different frequency response issues with the different mechanisms.

 

This seems to be the case with SMPS, there seems to be at least two different mechanisms that cause the leakage and they seem to have very different impedances. I don't know what those mechanisms ARE, i have not spent time in figuring that out, I'm not really interested in building my SMPS so I don't really care what actually causes it, especially since it will take a LOT of work to find out and I would much rather spend my time working on other things.

 

Leakage current causes issues in audio systems when it flows through a conductor, creating a voltage across that conductor which causes something to not behave the way you would like it. In some cases this is just directly creating noise on the shield of an interconnect and the receiving circuit sees this as noise. In a DAC this can show up as noise developed on a ground plane that can modulate an oscillator causing increased jitter on the clock.

 

There are two ways you can attenuate the leakage noise, you can put a resistance in series with it, or you can shunt it. Lets cover both of the separately.

 

The series resistor form works like this: you have the source impedance and you stick a resistor in series. Lets look at some possible values and outcomes. Say 100 ohm output impedance and you put 1 mega ohm in series, that is going to attenuate the noise drastically. But what if the source is 100 mega ohms, then that 1 mega ohm resistor is not going to do very much (a VERY slight attenuation). So for high impedance series resistor works good for lower impedance source, but not well for high impedance source.

 

The shunt form works by shunting the source around your source around the "test point", frequently to ground. Say you have the 100 ohm source and you shunt with 1 mega ohm, nothing happens, but of the source is 100 mega ohms, that 100 mega ohm shunt will dramatically decrease the amplitude.

 

I know the output of the SMPS is a combination of impedances by running a bunch of these shunt and series tests with different values and seeing what I get. The only way to get the results I saw is if the source consists of both high impedance and low impedance components at the same time.

 

The upshot is that it takes BOTH methods to get rid of the noise, both a shunt and a series.

 

John S.

 

 

 

 

[JohnSwenson]

15 hours ago, sandyk said:

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

Hi Alex,

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.

[JohnSwenson]

13 hours ago, sandyk said:

 

 

Comments Please ?

 

Alex

Highly unlikely.

 

Traditional "ground loop" which most articles on audio ground loop talk about is caused by induction of AC (hot/neutral) to safety ground. This only shows up if there is a long distance run of line wiring from one location to another. Such as you have 200 feet between your preamp and power amp. 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.

 

In all the playing around with leakage testing I have been doing, including between circuits with a long path back to the panel, I have not once had a case of traditional ground loop, it has all been leakage.

 

So the probability of fixing leakage issues with ground is VASTLY higher than it will cause a traditional ground loop.

 

If someone is actually getting nasty buzzing when grounding chassis  there is probably something wrong with the wiring.

 

John S.

[JohnSwenson]

1 hour ago, thyname said:

This is extremely difficult for me to understand. Way over my head. And I am pretty good technically, as a user.

 

So, maybe too much to ask, but it would be ideal if an extremely nice gentleman or gentlewoman can:

 

1 - Post an instruction video on how to do this

 

2 - Links to Amazon (or elsewhere) for each of the three components needed

 

Maybe just a wishful thinking from my part

If you don't want to build your own adapter you can buy the ifi groundhog, it does the same thing, but you don't have to build anything your self. It does cost $50 though.

 

John S.

[JohnSwenson]

2 hours ago, austinpop said:

A couple more questions:

 

Anyone have an Amazon link for this sucker?

 

And is that bare wire between the male and female DC terminal blocks?

The problem is there are no universal tags for this sort of thing. Cord end male plug gets some, grounded AC plug gets some, 3-pin AC plug gets some. You do NOT need an expensive audiophile plug.

 

Personally I think its best to go to a local hardware store, go to the electrical department and ask for a 3 pin AC plug, they will get you the right thing. The one shown was $3 at my local hardware store.

 

The CATV screw connect barrel plugs and jacks are best to get on amazon.

 

I just took some 14 AWG solid core wire I had in the drawer, stripped the insulation off and cut two short pieces. It doesn't have to be 14AWG anything from 18-14 will work great. Its easiest to use solid wire, you don't want to put stranded wire into the connectors, it is too easy to miss one strand which then coils around and touches the other side. You can use stranded wire if you tin the bundle first (twist the strands together then apply solder) this way you cant have an escaping strand.

 

Yep, mine was bare wire, with the large solid core wire there is no way they are going to wind up touching each other. It doesn't HAVE to be bare wire, that was just easier to do.

 

John S.

[JohnSwenson]

On 10/23/2017 at 9:33 AM, thyname said:

Do we have to do this for every single SMPS we have to avoid any leakage in the circuit, or just for the device we want to "fix" (i.e. in my case the router and the switch)?

 

Anyone willing to do this for me? Willing to pay for the parts, shipping and labor. I am in USA (DC area). I am terribly scared of messing with many electric stuff due to an accident when I was little.

 

Thanks!

LPS in general have primarily the lower impedance leakage.

 

The problem with using a linear supply is that the output may not be grounded. An ungrounded output will not shunt the high impedance leakage from other network devices when used with one of the named switches. (other switches don't block network leakage whether they are grounded or not.

 

Thus if using one of the named switches AND using an LPS you still need to ground the output, not to shunt high impedance leakage from the lps, but to shunt the high impedance leakage coming from other devices on the network.

 

John S.

[JohnSwenson]

2 hours ago, Bricki said:

?no worries. Sorry for the confusion. I made 2 "Swenson" grounding adapters. I put 1 between the 12v dc input smps on my router/modem. I put the other one on the 12v smps input on my sonicTransporter (roon core). I did this instead of purchasing the netgear switch John suggested so I could continue to use my 5v dlink switch running on battery. 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 ???

 

Ps... The lps1 powered sms200 is also attached to the dlink 5v switch - but I didn't attach a grounding adapter here because if I read john's post correctly it would be of no benefit 

If the LPS-1 is powered by an SMPS, it is still a good idea to ground the output of the SMPS (NOT the output of the LPS-1) in order to make sure that the high impedance leakage doesn't find some path into the audio works.

 

John S.

[JohnSwenson]

Not really,

the shunt is to ground, that is what this thread is all about, the series has to be in series with the leakage, in this case it is the DC power, putting 100Mohm in series with the + and - of the power supply is not going to do any good, yep is will block the low impedance part, but you won't get any POWER through to run the device!

 

In some cases it is possible to block the low impedance part on SIGNAL connections, if the connection is all right with several K ohms in series. This is how the connection with a switch works, the transformers are 100 ohms impedance for the high frequency Ethernet signal, but in some cases can be significantly higher for the lower frequency leakage current, which is enough to block the low impedance leakage.

 

John S.

[JohnSwenson]

3 hours ago, BigGuy said:

Yes, this impedance issue IS confusing so I appreciate you and John having the patience to simplify so more of us can understand.

 

Leakage current has been around since AC power went into houses. All AC power supplies have it in some form, including linear supplies. In the 60s a couple engineers actually measured and modeled leakage current in audio systems. Given the time frame it was all from linear supplies, SMPS were a long way in the future. Different LPS implementations turn out to have significant differences in the leakage they produce.

 

In the audio relm the effects of leakage that were important concerned generating voltages across loads and sources, even with tube circuits these are usually significantly less than 1 Mega Ohm, thus in what I am calling the "low impedance" range.

 

This analysis of leakage current became quite important in the emerging medical instrumentation business (heart monitors etc), since electrical equipment was being deliberately connected to human bodies it was very important to know if this leakage current could be dangerous to humans. Since they are worried about mA range of current the leakage that was important had to be fairly low impedance to generate significant current. Thus a LOT of leakage analysis, testing tools, testing standards etc were focused on low impedance leakage. It was not specifically decided to ignore high impedance, but the effects of interest could only be produced by low impedance leakage, so that is what was studied.

 

The result of this was that all leakage testing was done with circuits and test equipment that was designed to work at 1 Mega Ohm or less. With linear supplies this was perfectly sufficient.

 

Then along came SMPS. It turns out that SMPS are very different with regard to leakage then LPS. First is frequency, linear leakage is power line frequency related (60, 120, 180 etc), but SMPS have a huge range of frequencies due to the switching nature of their operation. They ALSO include the traditional 60, 120, 180 etc.

 

SMPS have been extensively tested for leakage, but it has been done with all the existing test equipment and methodologies, thus focusing on low impedance leakage.

 

Unfortunately it turns out that SMPS also include a high impedance component to their leakage, this is way above 1 Mega Ohms. The problem is that the existing test equipment and methodologies shunt this high impedance leakage to ground so they never see it. So nobody knew it was there. This high impedance leakage is significantly higher in intensity than the traditional low impedance leakage, so it can actually have a significantly larger affect on audio systems than traditional leakage, but nobody knew it was there.

 

Do not confuse the high impedance with high frequency. The SMPS contains high and low impedance components at all frequencies. Thus even at 60 Hz, there are both high and low components. This MUST mean that there are at least two different mechanisms contributing to the leakage simultaneously. One with a high impedance and one with a low impedance. The same thing happens at the higher frequencies. That amplitude ratio between high and low impedance varies with frequency (this is varies radically from one model to another), but both components seem to exist across the frequency range.

 

Currently I do NOT know what these mechanisms ARE, just that they must exist due to the behavior of the leakage. So please don't ask what is causing this, I don't know.

 

If you have leakage from a source (PS), it can show up in several ways. One is direct flow to earth ground. If the PS that is the source of the leakage has an electrical path to something that is grounded (such as a DAC, preamp, poweramp etc), maybe an interconnect, USB cable, Ethernet cable etc, the leakage current will create a voltage across the impedance of the cable, frequently the "ground wire" or shield of the cable. This can add noise to the intended signal. This is how leakage current has traditionally shown up in audio systems, as low frequency "hum or buzz" at the preamp or poweramp, because they were grounded.

 

Another way leakage can get into systems is through a DAC, the leakage current can go through the ground plane of the DAC PCB, that current creates a small voltage which modulates the oscillators(s) producing the clocks in the DAC, adding jitter to those clocks. Even if the leakage doesn't get to a preamp or power amp it can add jitter to the clock in the DAC, thus subtly distorting audio output.

 

This leakage from a computer through a DAC has been particularly important in computer audio since most computers are powered by SMPS.

 

In both the above cases the leakage here is composed of both the high impedance and low impedance components.

 

The leakage current does not have to go directly to an earth ground, it can also go from one power supply to another power supply, even if both have two prong plugs. This is what I have called a leakage loop. I have already written extensively about leakage loops so I am not going to go into it here.

 

So how do I know high impedance leakage exists and how do I measure it? A couple months ago I was looking into leakage current and was trying out several different detector circuits and started seeing very strange results that didn't make any sense. I ran a whole bunch of tests on different SMPS models and had a hard time coming up with correlations, things just were not making any sense.

 

I was trying to figure out what could be causing this. After many weeks of trying different things it started to look like the leakage might be very high impedance (over a hundred Mega Ohms). A few simple tests confirmed that this was in fact true. (I still didn't know it was BOTH high and low at the same time). But that presented a quandary, how in the world do you measure that. All my test equipment maxed out at 10 Mega Ohms which make it impossible to properly measure such high impedance signals. It turned out I couldn't even buy test equipment for this (at least not that I had any chance of affording) so I had to build my own. That took a little while to design and build, but I finally had a differential probe with around 10 Giga Ohms input impedance, AND very low noise.

 

With this tool I could now properly measure this very high impedance leakage. Unfortunately it was STILL doing really weird things. Another round of tests revealed that the leakage was composed of both a high impedance and low impedance part at the SAME frequency. Wow that was something I had not anticipated. I devised a series of tests to check this and sure enough, the results clearly showed both a high impedance and low impedance component at the same time from the same supply.

 

Unfortunately this makes dealing with leakage way more complicated than I had ever imagined. All the methods I had been using and discussing for getting rid of leakage were all focused on the low impedance component, which work for that, but frequently don't touch the high impedance components.

 

So how do you deal with leakage now that we know about both the high and low impedance components? It turns out that there is no single method that works well for both, so you have to come up with different methods, one for high and one for low and figure out how to apply them together.

 

There are two broad categories of how to stop leakage:

1) series block

2) shunt

 

Series block sticks something in series with the leakage path which prevents the leakage from going through. But in order to be useful it has to let whatever the signal is go through. This manifests itself with various isolation schemes that have been tried over the years. These work by increasing the impedance to the leakage, but still letting the signal go through. These work fairly well for the low impedance components, but the rise in impedance for the leakage is not nearly high enough to block high impedance components, they sail right through these isolation mechanisms.

 

This is where the shunt comes in. It turns out it is very to get the high impedance components to shunt around your sensitive components, instead of trying to block them, you just make them go somewhere else. The easiest way to do this is to shunt them to ground and the power supply itself. It CAN be done in other parts of the system, but shunting to ground at the source is the easiest way to deal with it.

 

Unfortunately the shunt does not deal with the low impedance part. So you need to do BOTH the shunt to ground and the series block.  THAT will get rid of it all.

 

The series block is going to be different depending on what the "signal" is. For a power supply the "signal" is DC power. So just sticking in a resistor is not going to work, it will block the leakage but it also blocks DC. SO you need to get more creative. A magnetic circuit that passes DC but blocks 60Hz and up would work, but that is very large, heavy and expensive. This is where the LPS-1 comes in, it blocks all low frequency leakage, but does not block the very high impedance leakage. So use either an LPS to drive it or an SMPS whose output is grounded to shunt the high impedance component.

 

For high frequency signals such as Ethernet the existing transformers are sufficient to block the low impedance components of leakage. Leakage even from SMPS is still significantly lower in frequency than Ethernet signalling so a properly designed transformer will have a high enough impedance at the lower frequencies to block the low impedance components, but NOT the high impedance components. SO you still need to shunt the high impedance components and the transformer will take care of the low.

 

Theoretically you could do the same with USB, BUT USB is not just AC, it requires DC connectivity through the data pair, so a transformer will not work. This has made series blocking very difficult to deal with. There are a few solutions, but none of them block the high impedance components, so you still need to shunt the all the high impedance source before they get to the USB cable if you want to stop ALL the leakage from getting through to a DAC. 

 

Stopping the low impedance leakage from getting through an audio interconnect is a difficult task. The leakage and the audio are in exactly the same frequency range so you can't separate them that way. The only known way to do this is with a balanced system. In many cases the leakage will be the same on both signal wires, but the audio will be differential, a proper differential input can block the leakage. BUT most implementation will NOT stop the high impedance component, so you STILL need to short it out before it gets there. Unfortunately not all balanced system are created equal. There are several implementations that do the differential input in such a way that it still doesn't block low impedance leakage. So a differential input MAY block low impedance leakage, it may not. Its best to get rid of it before it ever gets to the audio section in the first place. 

 

Wow that was a lot longer than I thought. I hope this makes sense and is useful to people.

 

John S.

 

 

 

 

 

[JohnSwenson]

52 minutes ago, Em2016 said:

 

Hi John, epic explanation.

 

Does this mean even the Intona fails to block high impedance components?

 

Yes, that is correct.

 

John S.

[JohnSwenson]

10 hours ago, jabbr said:

@JohnSwenson nice investigation  

 

Help a simple country boy out please: the term “high impedance leakage current” is making me a little dizzy as I try to drink my coffee on this Sunday AM. Impedance isn’t a term normally used to qualify a current so perhaps we should rename this before it takes on a life of its own — you mean “high voltage/impedance” = current ... what is a better term? 

 

Also these currents are going to be way more important at higher frequencies. I think if a circuit were made available to precisely illustrate the excellent point you are making here (this is all about parasitic capacitances and inductances) this frequency point will be better illustrated. (Yes— high impedance probes are essential when working with RF)

All current comes from some form of voltage between two points. No real voltage source is perfect, there will always be SOME impedance in series with that voltage. It might be 1 ohm it might be 1 mega ohm it might be 300 mega ohms.

 

This impedance shows up in what happens when you connect a resistance across the voltage source. For example if you have a 1K impedance source and put a 1 ohm resistor across it, you will get a very large voltage drop. If you put  a 1 mega ohm resistor across the source you will barely have any change. If the source is 300 mega ohms and you put a 1 mega ohm resistor across it, the voltage drop is large.

 

In the case of SMPS leakage there seems to be both a high impedance component and a low impedance component. At low frequencies the impedance was very high, about 300 mega ohms. I determined this by trying different resistors in series and to shunt to ground.  But it wasn't behaving correctly. I put a resistor in parallel that should have dropped the level by 80dB, but it didn't it only dropped by 30dB. Then I tried putting a medium range resistor in series, and it dropped down to below the instrument floor. The only way this can happen is if the source has at least two sources, one very high impedance and one much lower.

 

The source impedance DOES vary with frequency, but no where near close to what it would be if it was just a capacitor from AC line to output. It seems to be way more complex than that.

 

John S.

[JohnSwenson]

20 hours ago, gstew said:

John & Alex,

Thanks for the great explanations & education on how AC power supply leakage works, how & why it was characterized, why that characterization missed the 'high-impedance' type of leakage, and what you can do to diminish its effects on our audio systems.

The wealth of information you've both shared here (and embodied in your products) has made a world of difference in the sound quality of many audio systems, mine VERY much included.

Please help me make sure I have understood all of this...
 

Your first section is all correct. Now on to the questions:

 

#1:  linear supplies still have leakage and shunted SMPS (not going through a LPS-1) still have low impedance leakage. You can still have effects from this. This is where my posts awhile back on leakage loops can come into play. Particularly the parts about keeping the impedance on the AC line between devices as low as possible.

 

In your specific application there is no easy way to tell whether SMPS or LPS is going to sound better in your amps, it very much depends on the implementation of both.

 

#2: I did a bunch of tests and this and did not see ANY increase in leakage when using a switching DC-DC converter.  They CAN produce all kinds of radiated noise (primarily from unshielded inductors and poor PCB layout) and high frequency noise on both the output and input. All of these can be very effectively dealt with, shielded inductors and good PCB layout dramatically reduce emissions, and proper filtering can almost eliminate the electical noise. Putting a good linear reg after the DC-DC converter can essentially eliminate the noise on the output. In particular the LT3042/LT3045 are particularly effective in getting rid of noise from switching converter. The combination is a very useful tool, the switching converter can handle large differences in input and output voltages, producing a voltage just a little bit above the output voltage and the linear reg can clean up the output without generating too much heat.

 

#3: Grounding the output of a linear supply may help some. It depends a lot on the leakage coming out of the LPS. I can't say it won't help at all, but it is not going to be anywhere near as dramatic as with the high impedance of the SMPS. I measured about 4 LPS and 2 of them had no difference at all when grounding, one made a small difference and one was a little bit larger difference.

 

#4: Correct, leakage is usually independant of other properties of a linear supply.

 

The ps section:

Un-damped linear supplies can have their transformer resonances excited by high frequency noise on the AC line. This can come from other LPS or especially from SMPS. The broadband high frequency noise from an SMPS can easily excite a non-damped linear supply. SMPS don't have these resonances so don't have this issue. This resonance exciting noise is high frequency so it CAN be blocked by a Topaz or similar transformer. A Topaz blocks noise starting at around 400Hz, so it is great at blocking this high frequency noise, but it does NOT block the low frequency part of leakage (60, 120, 180 etc).  This may contradict the "put everything on the same strip rule", if the leakage from the SMPS is already dealt with, then putting on the other side of a Topaz from the component with a linear supply can make a big difference.

 

pps:  In a linear supply the leakage mostly comes from the transformer and relates to how it is physically built. I have not spent any time trying to make generalizations based on transformer construction and leakage, I'm sure they are to be had, I just haven't done the testing.

 

John S.

 

[JohnSwenson]

3 hours ago, BigGuy said:

charlesphoto's post raises a question for me.

I understand that the PS for a router should have DC grounded but is it important to go upstream to the modem as well?

 

IF so I need to get a power extender strip with a lot more outlets...or find a source for inexpensive grounded LPS of varying output voltages for all these accessories! 

I'm sorry, I guess I didn't explain this well enough. IF the last switch before your audio endpoint (computer, renderer etc) is one of the named switches (FS105 and FS108) AND you ground the power supply driving THAT switch, you do NOT, repeat NOT have to ground the SMPS from any other upstream network devices, period. Grounding the PS to one of those switches will get rid of the leakage from all the other network devices you have. This is why I am singling them out, if you have one of these as the last switch, (and ground its PS) then you do not have to worry about leakage from anything else on the network, period.

 

John S.

[JohnSwenson]

4 hours ago, thyname said:

 

Great explanation!

 

What about the scenario when no switch is involved (audio streamer connected directly to router), would grounding the router would take care of everything in the house, including another location that has a Switch? Or does this just work with the two FS105 and FS108 models you tested? Thanks!

What I have found is that most wired Ethernet devices (switch or otherwise) do NOT block leakage from other connections passing through them, even if their power supply is grounded. The exception seems to be a few switches, that when their power supply is grounded block leakage from other devices.

 

Thus grounding the PS to a router is probably NOT going to block leakage from other devices plugged into it.

 

If you cannot use one of the specified switches as the last point in front of your audio endpoint, then your best bet is to add one, they are not very expensive, just make sure you ground the power supply going into it. This arrangement will make sure that whatever leakage is going on in your network will not make it through into your audio system.

 

John S.

[JohnSwenson]

3 hours ago, BigGuy said:

I see that there is a screw GND terminal on the back of the Netgear switch. 

 

Does that terminal need to be connected to ground using John's umbilical (modified with spade connector, etc.) IN ADDITION TO grounding the Netgear power supply?

 

At this point I think the only thing not grounded is me!  ;-)

The ground screw terminal on some Netgear switches is JUST connected to the metal box, it is NOT connected to the groundplane on the PCB. The groundplane is what needs to be grounded, so just grounding the screw does NOT improve leakage. The only way to be sure you are grounding the groundplane on the PCB is to ground the negative of the power supply, this is always connected to the groundplane.

 

John S.

[JohnSwenson]

Update on network leakage issues

 

One of the members sent me a Netgear GS105 to test, it comes out almost as good as the FS105. I have not tested the GS108, but it is PROBABLY the same as the GS108.  The one I tested is the V5 version. I can make no claims as to other versions. I can say that for the FS105, both the V2 and V3 (latest version) were both good, so an earlier version of the GS105 has a good probability of also working well.

 

So at this point I think it is safe to say that the current versions of Netgear switches, FS105, FS108, GS105 and GS108 are the list of switches that can be used to to block network leakage from getting into your audio system.

 

Do NOT assume that other models or device types (routers, modems, APs etc) will also do so.

 

It takes a huge amount of time and frustration for me to do these leakage tests. At this point I am through with it, period. Please do not send me anything to test or ask that I test some specific device you have or want to buy. I will not test it.

 

In the last several days I have written several posts that I hope will explain how to use this information, I'm not going to re-write all of it here in this post, just scroll up and read my my last several posts in this thread.

 

One thing that hasn't been covered is what if you have or are buying one of those "audiophile" switches? I have not tested nor will I be testing any of those for their leakage characteristics.

 

Remember that the leakage comes from an SMPS connected to something on your network. Thus if you are using one of the audiophile switches you need to make sure it is powered from an LPS, OR powered from an SMPS with the negative output grounded. This makes sure you are not adding leakage through this switch. To make sure you are not getting leakage from other devices on the network put one of the above named switches (with grounded SMPS or LPS) in front of the audiophile switch.

 

These switches are not expensive, if in doubt just add one in front of your AE. If it is not the last switch before the AE just make sure that the last one is powered from grounded SMPS or LPS.

 

One other thing I have been finding is that common UTP (Un-shielded Twisted Pair) Ethernet cable radiates leakage current like mad. Since leakage is common mode, it doesn't matter that the cable is twisted pair since the same thing is on both wires. These cables make beautiful antennas for leakage. This MAY be why some people like to use shielded Ethernet cables with their audio systems. This also means that if you use one of the above switches, there is no leakage current going through the "output" Ethernet Cable so there can be no radiation from the leakage, because there isn't any leakage going through the cable.

 

This also means that if you do use one of these switches to block leakage it should probably be somewhat far away from the audio system. If the switch is right in the rack with your audio stuff the cable going to the rest of the network can be radiating noise into your audio equipment. If the switch is further away, the only Ethernet cable near the audio equipment is the one without leakage.

 

I hope these recent posts are sufficient for you all to use the information, I really want to get on with things and spend my time developing the new ground breaking products we've been dreaming up.

 

John S.