Alleged Y cap issue attributed to Bruno Putzeys

[BR52]

At the device or in general?
Cause I was there when then putted this rods deep tn the ground with that braided copper huge ribbons when I built my house and measured them (I *think* the regulation states that this must be a few Ohm,6?,8? I don't remember)

Also outlets are also checked and I have a dedicated phase for my gear,I have seen what led,motors,etc do when they share the same phase when I do my silly measurements.
The nicest gear about it had an indicator which showed if it was at the wrong direction.
I have also seen wrongly internal wiring.

To give a general answer is not possible. Depending on the country where you live, much different mains topologies exist. Star, Delta, Unsymmetrical.... what is thinkable exist, unfortunately. In your case, I would check the PE connection beginning by the appliance step by step to the house inlet. Here in Germany, we have 99% Star cabling, with the N connected to PE in the House inlet and also connected to the base grounding at this point. Some houses with only one phase inlet following the same scheme. In older times, the PE was connected to N individually on each wall outlet, but this is history (hopefully). For your information, we have 230V phase to N and 400V phase phase. For more help, I need more information about your mains topologies.

 

[Sokel]

To give a general answer is not possible. Depending on the country where you live, much different mains topologies exist. Star, Delta, Unsymmetrical.... what is thinkable exist, unfortunately. In your case, I would check the PE connection beginning by the appliance step by step to the house inlet. Here in Germany, we have 99% Star cabling, with the N connected to PE in the House inlet and also connected to the base grounding at this point. Some houses with only one phase inlet following the same scheme. In older times, the PE was connected to N individually on each wall outlet, but this is history (hopefully). For your information, we have 230V phase to N and 400V phase phase. For more help, I need more information about your mains topologies.

230V mains,three-phase installation,star grounding at the main board,base grounding after that.
I think it's the same rule at all EU these days,my house is about 6 years old,3 floor which each floor has it's own secondary boards,different for low signals (network,phones,alarms,etc) and electricity.

To tell the truth all I involved with it is with that separate phase for my gear and some thick wiring for 20A fuses I liked to have.
And of course I insisted about proper ground and outlet wiring orientation but is pretty much a norm these days,not like older days.
All the rest was a nightmare to look at when it was installed,I didn't even want to look.

 

[BR52]

The connection to Planet Earth has little to do with day-to-day AC power quality.
That 80 to 120 Volts may be what electricians refer to as 'phantom voltage'. Add the smallest load or resistance and the voltage disappears.

Yes ,only with security, thats all.
The 80-120 on the case of the appliance is an indicator that a class 1 device has no grounding (no connection to PE) and this happens if the class 1 device is still OK because of capacitive coupling and so on. But Class 1 devices need the PE connection in a failure case internally (full throttle on the outside) so you need the low Ohm connection to engage the fuse in the distribution box.

 

[BR52]

230V mains,three-phase installation,star grounding at the main board,base grounding after that.
I think it's the same rule at all EU these days,my house is about 6 years old,3 floor which each floor has it's own secondary boards,different for low signals (network,phones,alarms,etc) and electricity.

To tell the truth all I involved with it is with that separate phase for my gear and some thick wiring for 20A fuses I liked to have.
And of course I insisted about proper ground and outlet wiring orientation but is pretty much a norm these days,not like older days.
All the rest was a nightmare to look at when it was installed,I didn't even want to look.

I remember the movie Lion King, the football game.

 

[BR52]

230V mains,three-phase installation,star grounding at the main board,base grounding after that.

It makes it easy to check the PE wiring because you can find the broken wire (connection).

 

[Sokel]

230V mains,three-phase installation,star grounding at the main board,base grounding after that.

It makes it easy to check the PE wiring because you can find the broken wire (connection).

Ok,here's what I did now,tell me if it's ok.

I connected the ground of an outlet directly below the board and checked it with the DMM against the star,it wrote 2 Ohm (edit.might be less than that cause the thin crocodile jumper cables I use to reach it have some resistance of their own) .
Now I got a long wire and tested all the outlets ground of my rig (6),they all showed 2.4-2.5 Ohm.
I then checked L-N and N-G and L-G.
The readings with the same order is 229VAC , 0.2VAC ,229VAC.

Thanks for that!

 

[pma]

As promised from another thread, am starting this thread to fact check a contention that Y caps cause audio problems (notably as applied in AC inlet filters) and that noted designer Bruno Putzeys had stated as such. Have seen this contention perpetuated here and on other sites and so would like to see if ASR experts agree or not (about Y cap application).

Here is some background from other sites on this contention...

Here is one notable Bruno P quote from diyaudio.com:

“Y caps: as have been noted, they capacitively couple the mains to chassis. In AES48 compliant balanced systems this is no problem because they keep signal and ground well separated. In an unbalanced system the leakage current will also flow through the ground wire or shield of your $$$$$ RCA interlink and thus add noise to the audio.
As such, Y caps are difficult to avoid, they serve a purpose after all (to keep rubbish generated inside the box from getting out), but what it means is that it pays to try minimizing them. There are small Y caps in the SMPS600. Since they wholly suffice, there is no reason to compound them with external ones.”

If you look around, he talks about Y caps in many contexts. Notably both in a SMPS and in an AC inlet filter.

I agree with Bruno, as almost always. You know, he has a deeper view of a real circuit and amplifier designer.

Those caps are an issue especially in case of RCA interconnects. It is my pleasure to give an example, as I was measuring this issue recently.

Test path consists of USB powered DAC (Topping D10s) connected to a notebook, RCA cable 1m from DAC to the amplifier and the old class AB amplifier module. The amplifier is supplied from SMPS power supply, 2x27V. The case of SMPS is connected with PE and the SMPS has Y capacitors and leakage current flows to PE. However, outputs (+, 0, -) are floating and the amplifier module is thus in class II.

Now, 2 scenarios.

1) Notebook has class I power supply, so the DAC is also connected to PE via its USB cable. We have class I source to class II amplifier. Spectrum looks like this:

Please note the 50Hz + odd multiples that are completely a result of the capacitive leakage current flowing through the RCA cable shield. The cable is a good RG-59.

2) Notebook has class II power supply, not connected to PE. Now we have class II source to class II amplifier. Stray capacitance is reduced to notebook power supply stray capacitance. And the spectrum:

The 50Hz and odd multiples are almost completely gone. So, you can see the effect of leakage currrent through the Y capacitors in a real world.

 

[BR52]

I guess in the discussion, we see two aspects of grounding class 1 devices: for audio, the effects of capacitive coupling and the security aspect to protect people with grounding.

 

[pma]

Yes, and security standards often go against signal optimization regarding SNR.

 

[BR52]

Ok,here's what I did now,tell me if it's ok.

I connected the ground of an outlet directly below the board and checked it with the DMM against the star,it wrote 2 Ohm (edit.might be less than that cause the thin crocodile jumper cables I use to reach it have some resistance of their own) .
Now I got a long wire and tested all the outlets ground of my rig (6),they all showed 2.4-2.5 Ohm.
I then checked L-N and N-G and L-G.
The readings with the same order is 229VAC , 0.2VAC ,229VAC.

Thanks for that!

In a post before, you told us you could measure 70,80 to 120 Volts (High Ohm DMM ?)from the case to ground (PE ?) was it a class 1 device? Where was the ground (PE) located?

 

[Sokel]

In a post before, you told us you could measure 70,80 to 120 Volts (High Ohm DMM ?)from the case to ground (PE ?) was it a class 1 device? Where was the ground (PE) located?

It was an old Pioneer CDP,the reason I measured it is that you could feel the tinkle if you touch it.
However changing the outlet orientation was ok.Never opened it to see what is going on,if I remember right it was class II,2-prong plug,no ground.

(my DMM is a true RMS Extech EX520,the same I measured this stuff today)

 

[BR52]

Yes, and security standards often go against signal optimization regarding SNR.

Both aspects coming together in medical appliances because Humans are very sensitive to tiny
currents in the body if the skin is broken (surgery etc.)

 

[pma]

Both aspects coming together in medical appliances because Humans are very sensitive to tiny
currents in the body if the skin is broken (surgery etc.)

Of course, and I expect we all know. This will probably never be a case in audio, for the high cost reason. All the signal links through optical fibres would be a less expensive cure, total cure. Of course with better link than consumer grade Toslink.

 

[pma]

In a post before, you told us you could measure 70,80 to 120 Volts (High Ohm DMM ?)from the case to ground (PE ?) was it a class 1 device? Where was the ground (PE) located?

Quite usual value (in class II). Measure current as well to get the impedance.

 

[AnalogSteph]

Test path consists of USB powered DAC (Topping D10s) connected to a notebook, RCA cable 1m from DAC to the amplifier and the old class AB amplifier module. The amplifier is supplied from SMPS power supply, 2x27V. The case of SMPS is connected with PE and the SMPS has Y capacitors and leakage current flows to PE. However, outputs (+, 0, -) are floating and the amplifier module is thus in class II.

The amplifier power supply must have a reasonably substantial pri/sec leakage current path unrelated to the "official" mains filter going to PE then... I can't explain your results any other way.

 

[pma]

The amplifier power supply must have a reasonably substantial pri/sec leakage current path unrelated to the "official" mains filter going to PE then... I can't explain your results any other way.

No, the amplifier is a module supplied from external SMPS. To me the case is absolutely clear as ABC, leakage current from SMPS flows to amplifier analog ground (0V), continues along/through RCA cable shield to DAC signal ground and then via USB cable and notebook supply to PE. On the way it creates voltage drop across RCA cable shield, this error voltage is added to signal voltage and amplified by amplifier gain and measured in the spectrum. This should be perfectly understandable. The leakage current from SMPS 0V terminal flowing to PE via RCA cable is measurable even by a DMM.

 

[HaveMeterWillTravel]

Quite usual value (in class II). Measure current as well to get the impedance.

IIRC, the effect manifests in the current domain. What ever voltage one measures is really the induced voltage across the measurement devices input impedance.
Not unlike input bias currents of an op-amp.

 

[HaveMeterWillTravel]

No, the amplifier is a module supplied from external SMPS. To me the case is absolutely clear as ABC, leakage current from SMPS flows to amplifier analog ground (0V), continues along/through RCA cable shield to DAC signal ground and then via USB cable and notebook supply to PE. On the way it creates voltage drop across RCA cable shield, this error voltage is added to signal voltage and amplified by amplifier gain and measured in the spectrum. This should be perfectly understandable. The leakage current from SMPS 0V terminal flowing to PE via RCA cable is measurable even by a DMM.

It is predominately a common mode and not differential 'noise'. More current will flow along the RCA shield as it's a lower impedance path than the center-pin's path. While it is challenging to measure, the voltage differential between RCA shield and pin at the "downstream" will be similar. So it's not really a differential voltage being amplified, per say. But rather, it's trying to amplify a small signal in the presence of a large common mode voltage relative to it's own reference. Most non-differential audio input stages are simply not designed with high CMRR in mind. The pin-voltages are similar in a balanced/differential input stage such as an XLR or TRS. The difference is that type of input stages generally have far better CMRR capabilities.

There is no (inherent) reason why an RCA input could not also be balanced/differential with a high CMRR. But XLR's and TRS already exist, so why invent the wheel for audio?
"Two wire" balanced/differential signals exist in other applications. 4-20mA loops are perhaps one of the most common.

 

[solderdude]

DIN audio (5 pin) had voltage signals for playback (pin 3 and 5) and current for recording (1 and 4), 2 is common.

Biggest issue usually in audio is leakage currents trying to equalize between 2 devices via the shield (audio ground) adding a small (unwanted) voltage drop over the common wire which adds to the audio signal.
As the shield of the RCA is usually connected to common and mostly also to the chassis (which may or may not be connected to safety ground) it will be impossible to make that connection balanced (and thus have high CMRR). Cable then also would not have to be shielded but twisted or the 'common wire' should not be connected to the chassis and the only the chassis would be connected to shield (and thus have 2 signal wires, one to common).

 

[HaveMeterWillTravel]

To add a bit more nuance to the "Y cap" element, they are actually used sometimes in a Type II power supplies. The difference is the are placed in a different location.
The primarily difference between a X and Y safety capacitor is their designed failure mode. X caps are designed to fail "open", with Y failing to a short.
So the selection is dependent upon it's location in the circuit. On the AC/Input stage of a power supply, having a cap which can fail as a short would be undesirable across line to line ( or line to neutral). So an X cap is generally specified. In an opposite fashion, a failure mode of a short is generally preferable for a capacitor between line (or neutral) to physical earth. So a Y cap is used.

On a Type II P.S. there is no physical ground present on the power inlet, so one can't install a cap there (regardless of type).

However, a capacitor across the transformer barrier sometimes is installed (primarily to provide a current path for the induced common mode leakage current across it) which may reduce downstream emissions. There, either a Y or X may be used. It comes down to a design decision on which failure mode is most appropriate for the application.

With respect to "medical grade" IEC 60601 the requirements are for a different kettle of fish, and as was mentioned they can actually have more EMI.