AC Polarity and the reduction of noise and hum

microstrip · Jan 22, 2017

mcduman said:
i live in the schuko land and here are my measurement with normal and reverse polarities.

Normal Reverse Result
(Volts) AC AC
Transport 110.3 114.0 ?
DAC 114.5 110.6 Change
Pre 39.2 84.8 ?

1. I did not measure current but was surprised the voltage reading was as high as 100v.
2. One unit showed a lower reading with inverted polarity so i changed its orientation and indeed it was noticeably better this way. (bass, stage depth, attack)

These are normal values - the modern VOM´s are high impedance, and most transformers are symmetrical. In the preamplifier the transformer was clearly asymmetrical , the proper position is the 39.2 reading. When readings are close as the transport and DAC you have to go by listening.

DaveC · Jan 22, 2017

microstrip said:
Unfortunately Frantz you choose the poor moment and subject to snipe someone in WBF. The original advice and recipe are absolutely safe and have been used by many audiophiles for more than 30 years.

I appreciate your constructive posts, but please explain me why reversing neutral and phase in a grounded plug in modern systems is a dangerous think. Europeans do it every day in their houses many times at 230V AC!

And yes, I know that in prehistorical times there was no separate ground wire and neutral was often used as ground, and some equipment dis not use power transformers and connected neutral to ground. Fortunately these days are gone, many people died because of it.

In CE equipment you'll be fine as both wires need to be fused apparently, but in the US it's common to have only one fuse on the hot side. So if there was an issue where a hot wire touched the chassis with hot and neutral mixed up the fuse could blow and still leave a hot chassis.

I've also heard of people doing this for a very long time though, even some advising others to file down the fat side on the US plug so you can insert it either way, and others that actually eliminate safety grounds. Of course both those things are a bad idea to do for more than testing, and it's also true that some US plugs ARE NOT polarized and can be inserted either way, but if they are there's probably a reason for it.

In any case I can't remember the last time I saw a news article about an electrocution death from a stereo system, but it must have happened and I wonder how frequent it is?

microstrip · Jan 22, 2017

DaveC said:
In CE equipment you'll be fine as both wires need to be fused apparently, but in the US it's common to have only one fuse on the hot side. So if there was an issue where a hot wire touched the chassis with hot and neutral mixed up the fuse could blow and still leave a hot chassis. (...)

No, in EC only one wire must be fused. Fuses are not expected to protect from electrical shocks. What protects us is the safety ground - all equipment with metal exposed parts must be grounded and houses have a differential breaker . Fuses are expected to save us mainly from fire. Europe has very strict and sometimes annoying regulations concerning electrical safety. Why do you think manufacturers are shipping amplifiers with insulated speaker terminals, and WBT, Mundorf and Cardas connectors are becoming increasingly popular?

DaveC · Jan 22, 2017

microstrip said:
No, in EC only one wire must be fused. Fuses are not expected to protect from electrical shocks. What protects us is the safety ground - all equipment with metal exposed parts must be grounded and houses have a differential breaker . Fuses are expected to save us mainly from fire. Europe has very strict and sometimes annoying regulations concerning electrical safety. Why do you think manufacturers are shipping amplifiers with insulated speaker terminals, and WBT, Mundorf and Cardas connectors are becoming increasingly popular?

You're right, not sure what I was thinking... of course the main breaker would trip immediately.

I have noticed those binding posts, and plugs in the banana slot, I guess to keep people from inserting power cables in the binding posts... it is getting silly.

amirm · Jan 22, 2017

microstrip said:
I was considering electromagnetic waves, not electrons.

Maxwell is no more your friend here than Ohm was. Your smartphone has no safety ground whatsoever yet tons of electromagnetic waves are running around there from those produced by the CPU/GPU running with multiple cores and high speeds to radio transmitter. Yet, you can play music on them and you don't hear those interferences. Ditto for your laptop. I did all of my critical listening tests on my laptop and found tiny impairments in ABX tests that folks would not even dare to try.

I also have portable volt meters that go way down to nanovolts and portable scopes that have no trouble delivering their spec without any connection to your ground rod.

All the shielding you want to do for RF and such can and is done with the return line of power. That and careful layout of the design is all that is needed and used.

Again think of how airplanes, cars, etc. work if a safety ground is needed to eliminate noise.

Just noticed that I have nothing to debate or learn from you.

I understand. Some things are too convenient and liked to let go. I mean who wouldn't like the concept of a sewage pipe out of your audio gear that take out all the bad stuff. I would too if it were true.

Alas that sewage pipe goes uphill, not down. It is so far away from your mains entrance that just like that sewage pipe, electrons don't want to go that path. Worse yet, that sewage pipe is actually hooked up to your water source as is the case with neutral and safety ground!

I can quote you tons of papers and authoritative references that show all of this both in practice and theory. The logic is bullet proof and used everyday to solve hum and ground loop problems. But we no longer discuss audio science here so I am just resorting to simple arguments that should convey the same concept.

So I am going to repeat again: there is no audio problem that the safety ground is designed to solve. It is there to keep you safe, that is it. Thinking of it otherwise and then proceeding to tweak it can be quite dangerous at worse, and at best waste of money.

caesar · Jan 22, 2017

On the subject of noise and hum, can DC current leak into your AC line to cause hum, or is this an urban legend? If so, how does DC leak in, and how can one remove it (and thus remove the hum)? Thanks

amirm · Jan 22, 2017

microstrip said:
I appreciate your constructive posts, but please explain me why reversing neutral and phase in a grounded plug in modern systems is a dangerous think. Europeans do it every day in their houses many times at 230V AC!

Doesn't look like you have sought to read Soundstage the article that is partially quoted in the OP's reference to a forum discussion. Here it is in its entirety: http://www.soundstage.com/weaver01.htm

"While you may initially assume the three pronged cords to be inherently better, due to their ability to introduce multiple grounds to the audio system, they actually serve to further complicate the ground looping problems. Whichever style plug your equipment uses, you will probably need to employee some "cheater" plugs to mechanically circumvent the power cord's polarity. These adapters are readily available at hardware and home building supply stores for about a buck. They are nothing more than an adapter built to accept three pronged polarized plugs on one side and offering only two blades protruding from the other. Unfortunately, most of them are similarly polarized on the output side by using the wide/narrow method. This means you will have to trim the wide blade (using a file) so you will be able to try BOTH orientations (WARNING - Some units may have their warranty voided if you bypass the direct ground! Read your owners manual. Furthermore, the use of 'cheater' plugs may violate electrical safety laws for your community. Proceed at your own risk.)."

So he is not talking about reversing the wires inside the plug as you say but using a cheater plug that is against code and hence his warning.

Just attempting to measure what is instructed in there could subject you to lethal shocks and shorts. And even if you are careful there, a lot of cheap voltmeters are poorly designed and I would not connected them to mains whatsoever. Only proven brands such as Fluke, Agilent, Tek, etc. should be used.

Now if this solved a real problem that would be one thing but as I have explained repeatedly, a high-end designer would not leave this stone unturned. Just contact them and ask if they think this is a problem in real installations.

amirm · Jan 22, 2017

DaveC said:
Just like the ground wire on single ended IC cables, the chassis ground may serve more than one purpose and in some gear it's connected directly to signal ground, so it may float with the signal and then it certainly may have an effect as it's part of the return signal path, and so are the ground wires in the power cables. So it's really not as cut and dried as you think Amir, and the standards for grounding components are not complete, designers do it in many different ways.

Chassis ground is routinely connected to signal ground. But that has no bearing whatsoever in what I have explained. The actual circuit ground (internal to the equipment) is what is doing work, not the chassis safety ground.

Also consider that in electrical systems isolation does not mean a brick wall so attempts by designers to isolate grounds is partial.

I have said nothing about isolating ground. I have explained that a redundant wire in your romex cable, AC plug or mains cable is not there for audio purposes. It is there for safety. That is its only job. Indeed there is no isolation there at all in grounded systems.

Basically, safety ground may also be signal ground and be part of the return signal path, and while this may be prevented to some extent it won't be perfect. Theory based on ideals and real life sometimes don't quite match up...

There better not be any "signal ground" traveling back through your mains connector to your panel. Lack of clarity around this topic is at the source of such confusion.

marty · Jan 22, 2017

I have been asked to post the original TAS article. Here it is. There is no mention of hooking up the ground plug again once the cheater plug is used to determine the lowest residual AC voltage between a particular chassis and the receptacle ground. I'm not sure where this leaves me as I'm a little confused both on the different views expressed in the thread about the mechanism of the putative potential benefit of doing what Weaver suggests, and also, on why simply strapping the chassis ground to the duplex outlet ground isn't beneficial? Specifically, what's the down side? I have used cheater plugs in the past (although I don't need them now) and am not dead yet, so that's encouraging. If they work to eliminate hum or noise, should one reasonably weigh their benefits vs risk?

microstrip · Jan 22, 2017

amirm said:
Doesn't look like you have sought to read Soundstage the article that is partially quoted in the OP's reference to (...)

My post #27 that you probably missed

microstrip said:
Again, no one wants to carry listening tests with cheater plugs. The cheater is only used for the short time measurement. If you then want to carry listening tests you should use two proper cables with ground.

And this optimization should be carried to ALL equipment, otherwise we risk increasing the current through the signal ground wires.

Properly carried this technique is SAFE. It is no where related to often referred craziness of operating equipment without mains ground.

Electrical codes should be respected, but they changed along the years. In the late 80's, most audio equipment coming from the US come with a two wire mains cables - today it will be immediately arrested at the customs!

DaveC · Jan 22, 2017

amirm said:
Chassis ground is routinely connected to signal ground. But that has no bearing whatsoever in what I have explained. The actual circuit ground (internal to the equipment) is what is doing work, not the chassis safety ground.

I have said nothing about isolating ground. I have explained that a redundant wire in your romex cable, AC plug or mains cable is not there for audio purposes. It is there for safety. That is its only job. Indeed there is no isolation there at all in grounded systems.

There better not be any "signal ground" traveling back through your mains connector to your panel. Lack of clarity around this topic is at the source of such confusion.

Well, you made a comment about chassis/safety ground having no effect on the sound, and that's not true for the reasons I mentioned, the safety ground and signal may be the same and the ground wire in your power cable may make the exact same connection as the ground wire in your interconnect cable.

If people are running multiple lines with separate ground (this is almost always the case) than the signal ground circuit may actually include the main panel/service entrance. Even if it's a single line the best possible scenario is having all the grounds tied together at the power distribution device, so your power cable ground and IC ground are, again, making the same connection.

So unless you think signal return path is completely inaudible (it isn't) then your statement that safety/chassis ground can't effect audio quality is false.

microstrip · Jan 22, 2017

marty said:
I have been asked to post the original TAS article. Here it is. There is no mention of hooking up the ground plug again once the cheater plug is used to determine the lowest residual AC voltage between a particular chassis and the receptacle ground. I'm not sure where this leaves me as I'm a little confused both on the different views expressed in the thread about the mechanism of the putative potential benefit of doing what Weaver suggests, and also, on why simply strapping the chassis ground to the duplex outlet ground isn't beneficial? Specifically, what's the down side? I have used cheater plugs in the past (although I don't need them now) and am not dead yet, so that's encouraging. If they work to eliminate hum or noise, should one reasonably weigh their benefits vs risk?

Two different subjects that are getting mixed - cheaters break ground and should never been used for any purpose. They are unsafe.

Reversing the hot and neutral in the power cord of your audio equipment if properly carried is harmless, but you should keep the safe ground!

This technique works perfectly with the safe ground connected. You only lift it to make the measurements.

DonH50 · Jan 22, 2017

caesar said:
On the subject of noise and hum, can DC current leak into your AC line to cause hum, or is this an urban legend? If so, how does DC leak in, and how can one remove it (and thus remove the hum)? Thanks

Yes, there can be a DC offset. The usual symptom is a buzzing transformer. It can come from numerous sources including poor grounding, asymmetry in the system, load imbalance, leakage, etc. Note someplace along the chain the AC signal must be rectified and leak through to the lines for this to happen. It is rarely a problem (but I have seen a - very - few cases) and I suspect the number of actual cases is far less than the number claimed by marketeers and consumers.

The usual solution is to AC-couple the input, easier said than down for high-current lines. Emotiva makes a DC-block device, some power conditioners/filter block DC, as do some UPS units, and there are commercial units available. Any sort of transformer isolation device will work, though of course excessive DC may cause the isolation transformer itself to buzz.

FWIWFM - Don

p.s. Just caught @microstrip's last post. I am not sure what "phase" means in this context; reversing "hot" and neutral is a major code violation here. We do have some old lamps that will shock you if neutral is not rightly connected (i.e. if you reverse the plug).

microstrip · Jan 22, 2017

DonH50 said:
(...) p.s. Just caught @microstrip's last post. I am not sure what "phase" means in this context; reversing "hot" and neutral is a major code violation here. We do have some old lamps that will shock you if neutral is not rightly connected (i.e. if you reverse the plug).

Just edit my post for those who do not read whole threads or came here occasionally to comment the few lines of the last post.

Thanks!

I would personally destroy or repair any equipment that will shock if I reversed the plug (this has already happened with an heater and an iron)

amirm · Jan 22, 2017

DaveC said:
Well, you made a comment about chassis/safety ground having no effect on the sound, and that's not true for the reasons I mentioned, the safety ground and signal may be the same and the ground wire in your power cable may make the exact same connection as the ground wire in your interconnect cable.

If people are running multiple lines with separate ground (this is almost always the case) than the signal ground circuit may actually include the main panel/service entrance. Even if it's a single line the best possible scenario is having all the grounds tied together at the power distribution device, so your power cable ground and IC ground are, again, making the same connection.

So unless you think signal return path is completely inaudible (it isn't) then your statement that safety/chassis ground can't effect audio quality is false.

Again, if your audio system is impacted by current flows in the chassis ground, then you need to use balanced connections. Screwing around with safety ground is not a solution. It is against code to lift it, it is unsafe, etc.

And no, current does not flow all the way back to the breaker panel when it has a much shorter impedance path between two pieces of equipment. It is that short flow that impacts your audio. If that flow exists, once again you need to use balanced connections which do not uses chassis as a reference.

And no, you cannot solve signal ground current flow with single point connection. Internal leakage current to the chassis will cause these currents to flow just the same. Once again, if there are audible problems, use balanced connections. That is what it is designed to solve.

DonH50 · Jan 22, 2017

Thanks microstrip. I've been skimming but know better than to post here unless it is very specific. DC on AC lines and AC leakage into ground (neutral or safety) is something I have experience with, though moreso for dairy farms than audio systems...

microstrip · Jan 22, 2017

DonH50 said:
(...) DC on AC lines and AC leakage into ground (neutral or safety) is something I have experience with, though moreso for dairy farms than audio systems...

I see, really much harder than homes ... Our house has three electric boards, all protected by 30 mA differential breakers. I had to fight with the technician, as according to the local electric code, only 300 mA general differential breakers are mandatory, the 30 mA are reserved for areas with water installations. But for extra safety I wanted the 30 mA ones everywhere. Against his will the guy did what I required, telling me they would trip down all the time and he would have to change them. In twelve years we had only a few trips, caused just by the heater and iron I referred, one old vintage amplifier and a leak in the garden lighting circuit caused by hams. This only proves he did a proper job in the whole new electrical installation! And yes, although the breakers have a test button I used a special plug with a 6800 ohm resistor between hot and ground to check the breakers!

mcduman · Jan 22, 2017

microstrip said:
These are normal values - the modern VOM´s are high impedance, and most transformers are symmetrical. In the preamplifier the transformer was clearly asymmetrical , the proper position is the 39.2 reading. When readings are close as the transport and DAC you have to go by listening.

micro,

thanks for looking at my numbers. although the variation in my transport and dac are not that high (3%) with normal and inverted polarities, i am bothered by the fact that, for the dac, i am getting a lower reading with reverse polarity. (i repeated the measurements with the same findings and i like the sound better with reverse polarity.) does that mean something in the power supply was designed poorly or wired incorrectly?

microstrip · Jan 23, 2017

mcduman said:
micro,

thanks for looking at my numbers. although the variation in my transport and dac are not that high (3%) with normal and inverted polarities, i am bothered by the fact that, for the dac, i am getting a lower reading with reverse polarity. (i repeated the measurements with the same findings and i like the sound better with reverse polarity.) does that mean something in the power supply was designed poorly or wired incorrectly?

No, manufacturers usually do not care of this aspect - power transformer leakage should be minimal and is not considered an important parameter. I would risk that there is a 50% probability we have to reverse polarity if we care about this aspect. Just guessing, I have no data on it!

DaveC · Jan 23, 2017

amirm said:
Again, if your audio system is impacted by current flows in the chassis ground, then you need to use balanced connections. Screwing around with safety ground is not a solution. It is against code to lift it, it is unsafe, etc.

And no, current does not flow all the way back to the breaker panel when it has a much shorter impedance path between two pieces of equipment. It is that short flow that impacts your audio. If that flow exists, once again you need to use balanced connections which do not uses chassis as a reference.

And no, you cannot solve signal ground current flow with single point connection. Internal leakage current to the chassis will cause these currents to flow just the same. Once again, if there are audible problems, use balanced connections. That is what it is designed to solve.

I never said to "screw around" with safety ground, but you CAN use it to minimize resistance between the grounds of components thus minimizing noise caused by currents flowing along the ground connections.

And YES, current may flow all the way back to the breaker panel under the conditions I described, which are very common. It's not distance, it's resistance and the return current , as you said, will follow the path of least resistance. Let's assume the IC cables have something like 22g wiring, which is typical, and the power system has 12g wiring and they both make the exact same connections. You can easily see that the safety ground system may carry MORE return current vs the IC cables. If you can't see this possibility you are being willfully ignorant.

Again, I never said a single ground will "solve" anything, the purpose of ground is to keep the same potential everywhere and this can be accomplished better by tying together the system grounds inside the power distribution device, rather than at the panel. If multiple circuits are used this issue can be sidestepped by installing a subpanel for the audio system or by using a power distribution device with an external ground connection for each distributor and tying them together.

Using balanced isn't an option with single ended gear, and with a bit of forethought on AC power delivery, including safety ground, it's rarely an issue. Balanced has it's own issues and using balanced in a home system is pointless and will result in poorer sound quality vs a well setup single ended system imo.

AC Polarity and the reduction of noise and hum

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