AC polarity - can it be measured on the output signal?

[lionear]

Hello Keith,

Let me first say a big Thank You for always providing a lot of technical info, in very accessible language.  Your posts are always interesting, provocative, balanced, courteous and fair.  You're a big factor in keeping this forum alive.  I'd like to tap your brain on something.

Here's my question:  Does mains polarity matter and is there a way to measure it in the audio signal?

I'm talking about measurements like THD, frequency response, distortion, etc.

I ask this because Enid Lumley wrote about this idea in the 80's.  It wasn't her discovery, she just got the word out - and got a lot of flak on it.

What I mean by mains polarity: One expects a component to be connected to Earth, Neutral and Live in a specific way via in a wall outlet.  It is, however, possible for things to get "reversed".  The Neutral and the Live wires to be connected in reverse in the wall socket.  But even if the socket is correct, there may be another error in the component itself e.g. the wires going into the transformer may be accidentally connected in reverse to the component's mains input socket.

The equipment will work regardless of orientation.  And the die-hard measurements group (Dr AIX?, The Audio Skeptic?)  may point out that the AC gets rectified into the same DC voltage and what the audio circuits care about is the DC.  So mains orientation should not affect the final output.  At a logical level, I have to agree with that.

But that does not square with my experience.  With the right polarity, there's a lower noise floor, greater transparency, neutrality, dynamics, blah-blah-blah.  This also works for TV's and computer monitors.  There's less "snow", better details in dark areas, the white areas are whiter (not just light grey) and the black areas are blacker (not just dark grey), blah-blah-blah.  (I think my coffee maker also makes better coffee with the right polarity....)

There is a test for correct polarity:
Do not connect your component to anything.  
Use a cheater plug for the mains so that there's no Earth connection.  If your component has a two-pin mains plug, then you're fine.
Connect it to the mains and switch on.  
Without touching the component with any part of your body, measure the AC voltage between the chassis and Earth (in the wall socket).
Switch off and flip the orientation of the power plug so that the pin that was going into Live in the wall socket now goes into Neutral.  You may need to use a cheater plug here.
Without touching the component with any part of your body, measure the AC voltage between the chassis and the Earth (in the wall socket).

Whichever plug orientation results in a lower AC voltage is the correct one.  I have never found a component that has the same AC voltage for both orientations.  

But the question at hand is: can one measure the effects of mains polarity on the audio signal itself?

(I think the effects on a monitor can be measured with hardware-based screen calibration equipment, and perhaps also by zooming-in on a screen capture.
If anyone has hardware-based screen calibration equipment, can you test this out on a TV or computer monitor?)

PS: I'm also curious about why the AC voltage is not the same for both orientations....)

[htinparadise]

Balanced A/C mains throws a pickle into most of your inquiry and likely would be an excellent solution to all of your above A/C questions.

Kindest regards,

HTinP

[frenchyfranky]

Basically and by definition AC (alternative current) doesn't have polarity... So, I really doubt that if you inverse the live and the neutral this can affect in any manner the results of an audio device, it is literally out of sens.

[Gary Cook]

As Franky pointed out above, AC (Alternating Current) alternates between plus voltage and minus voltage according to its frequency (hz);

So 6 volts AC at 50 hz looks like this;



So if we measure the voltage between the active and the neutral with a multimeter it will show 6 volts. In Australia for mains power, ie; 240 volts at 50 hz, generally the neutral is earthed at the power transformer substation. So the voltage between the active and the neutral is the same as the voltage between the active and the earth. Trying to test that in Australia results in an earth leakage detection and power can be interrupted. Obviously there is no (meaningful) voltage between the neutral and the earth.



Cheers
Gary

[lionear]

Thanks for the responses.

And I agree that Live reverses direction (60Hz in the US, 50Hz in other countries) so doesn't have a "polarity". I don't like the term "AC Polarity" either, but it's what I came across in the past.

Perhaps I am referring to "AC leakage" - the AC voltage between the chassis and Earth when the device is floated (isn't connected to Earth via the power cord). If you flip the power cable (so that the pins on the power cord that get connected to Live and Neutral on the power socket are reversed), the AC leakage is different. This is not logical but it's an empirical result.

The biggest difference I have measured was on a fridge in Thailand - 4 VAC one way, and 115VAC the other way!

My question is whether different AC leakage levels show up in traditional measurements like THD and frequency response.

(When it comes to TV's, perhaps one needs to measure the resolution... and "gamut"?)

[richardrc]

Gary in your example the voltage would read 4.24v RMS not 6v. We are now officially 230vac but mostly it is still 240vac, which gives you 339v peak in your example.
Cheers

[Gary Cook]

Nov 20, 2014 16:15:37 GMT -5 richardrc said:

Gary in your example the voltage would read 4.24v RMS not 6v. We are now officially 230vac but mostly it is still 240vac, which gives you 339v peak in your example.
Cheers

I was keeping it simple for the OP


Cheers
Gary

[lionear]

Nov 20, 2014 17:32:53 GMT -5 Gary Cook said:

Nov 20, 2014 16:15:37 GMT -5 richardrc said:

Gary in your example the voltage would read 4.24v RMS not 6v. We are now officially 230vac but mostly it is still 240vac, which gives you 339v peak in your example.
Cheers

I was keeping it simple for the OP


Cheers
Gary

richardrc
Some of the posts are quite simplified.  For example, the idea that Earth and Neutral are connected "at the substation" (though Planet Earth) is also a simplification.  It's what they teach about electricity at the high school level but Earth and Neutral are usually connected together at the circuit breaker - at least in the US.  And in some situations, one can get hum, voltage spikes as the A/C comes on an off, etc.  The simple theory suggests that each equipment is isolated from each other - in practice, they're all interconnected.

I am intrigued by the idea of "balanced mains".  Thank you, htinparadise.

[Gary Cook]

Nov 21, 2014 14:04:17 GMT -5 lionear said:

Nov 20, 2014 17:32:53 GMT -5 Gary Cook said:

I was keeping it simple for the OP

richardrc
Some of the posts are quite simplified.  For example, the idea that Earth and Neutral are connected "at the substation" (though Planet Earth) is also a simplification.  It's what they teach about electricity at the high school level but Earth and Neutral are usually connected together at the circuit breaker - at least in the US.  And in some situations, one can get hum, voltage spikes as the A/C comes on an off, etc.  The simple theory suggests that each equipment is isolated from each other - in practice, they're all interconnected.
I am intrigued by the idea of "balanced mains".  Thank you, htinparadise.

Not in Australia as far as I know, we are required to have separate grounding at each site.

Cheers
Gary

[lionear]

Nov 21, 2014 14:23:14 GMT -5 Gary Cook said:

Nov 21, 2014 14:04:17 GMT -5 lionear said:

richardrc
Some of the posts are quite simplified.  For example, the idea that Earth and Neutral are connected "at the substation" (though Planet Earth) is also a simplification.  It's what they teach about electricity at the high school level but Earth and Neutral are usually connected together at the circuit breaker - at least in the US.  And in some situations, one can get hum, voltage spikes as the A/C comes on an off, etc.  The simple theory suggests that each equipment is isolated from each other - in practice, they're all interconnected.
I am intrigued by the idea of "balanced mains".  Thank you, htinparadise.

Not in Australia as far as I know, we are required to have separate grounding at each site.

Cheers
Gary

Even if you have a physical ground into the Earth at each site, nothing is really going to go back to the substation.  The teachers should say that the electrical energy is converted to chemical energy and heat.  (There are also some devices that are better at being "electrical Earth" than Planet Earth.)

I think this is what happens in a house:
The Earth wire that runs through the power sockets in a home go into the circuit breaker.  The circuit breaker checks that the voltage in the Earth wire is not too far above zero (known as the discrimination voltage).  If the discrimination voltage is exceeded then the circuit breaker will disconnect the mains via a relay, which involves a coil.  Neutral is indeed the zero reference for the mains voltage and the coil uses Neutral to know what "zero" is.  Earth and Neutral are thus "coupled" via the coil.  (Once the Earth voltage leaves the circuit breaker, you can connect it to a physical ground.  But this isn't the only option.)

But I digress...... anyone tried out the leakage voltage and how it changes depending on the orientation of the mains plug?