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Why would reversing AC leads reduce hum in a component?

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Posted on February 10, 2017 at 08:00:37
jedrider
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Posts: 15154
Location: No. California
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I'm reading the spec sheet for the Parasound Z-Phono and they indicate that it has a switch for AC polarity to reduce hum.

I have a phono stage that hums (sometimes, always??) and I am wondering if that is a good solution? However, I also would like to understand the possible mechanism behind this??

 

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RE: Why would reversing AC leads reduce hum in a component?, posted on February 10, 2017 at 08:04:57
If you don't know what you are doing you are going to kill yourself or worse yet, your dog, your cat or some other person. So don't do it!
If Parasound puts that on their equipment then there is a design or manufacturing fault.

 

One possible explanation ..., posted on February 10, 2017 at 08:26:43
Sondek
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The Elfix polarity tester has been around for ages. It's device to help you identify the proper orientation of hot/neutral. There's a brief explanation of it at the link. I have one of these in a drawer somewhere that I bought a long time ago.

 

RE: Why would reversing AC leads reduce hum in a component?, posted on February 10, 2017 at 08:35:06
jad
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Posts: 228
Location: OH
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Back in the 60's before AC plugs had polarizing plugs if a component produced hum the fix was to reverse the plug in the duplex outlet. This was very common for separate amplifiers and pre-amps. Reversing the plug of one of the components would eliminate hum. I don't know why but that's what you did and it worked.

 

RE: Why would reversing AC leads reduce hum in a component?, posted on February 10, 2017 at 08:42:33
Tre'
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Posts: 17263
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why would reversing the feed to the primary winding of the power transformer cause a safety issue? That winding is not grounded.


Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Why would reversing AC leads reduce hum in a component?, posted on February 10, 2017 at 09:19:22
Ryelands
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Posts: 1867
Location: Scotland
Joined: January 9, 2009
why would reversing the feed to the primary winding of the power transformer cause a safety issue?

In and of itself, it wouldn't but, if performed - as is often recommended - by reversing polarity at the mains input rather at than the transformer input, it very likely means (at least in the UK) that the fuse is in the neutral line, not the hot.

Hobbyists who don't understand why that might matter should either steer clear of the "tweak" or seek expert help. I suspect Parasound's feature addresses the issue perfectly safely but I'd hesitate to encourage users to try the idea on other designs unless they know what they're doing.

Though the benefits of competently configuring the polarity of transformer primaries to minimise leakage currents (aka transformer "sexing") have been known for decades, I'd wager that the cause of the OP's hum problem lies elsewhere.

HTH

D

 

RE: Why would reversing AC leads reduce hum in a component?, posted on February 10, 2017 at 09:40:20
Lew
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Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
If there is a potential difference (AC voltage) between the grounds for any two different electrical outlets serving the same audio system, there is a chance for hum. What you are hearing is that 60 Hz AC voltage expressing itself as a signal. Tre' can explain it better than I. The best and safest cure is to use only one outlet for the entire system or to use more than one outlet where the grounds are at the same potential. From what I have read, there is no such thing as a "safe" cheater plug, although most of us are lucky enough to get away with using them without electrocuting ourselves.

 

Tre' Ryelands answered for me...., posted on February 10, 2017 at 09:56:38
Thank you Ryelands. I'm just looking out for the pet community.

 

Or for the more experienced..., posted on February 10, 2017 at 10:04:29
Any multi meter can tell you if the outlet is wired correctly. Using bayonet leads measure the narrow (HOT) slot to the ground (round) hole. It should be 120vac. Do the same for the wide (Neutral)slot, it should read a few volts to zero.
If these results are not what you see the outlet is wired incorrectly and you need to seek professional help.

 

RE: Or for the more experienced..., posted on February 10, 2017 at 12:39:38
Sondek
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That is not quite the principal the Elfix works on, although in the end it is about hot/neutral orientation. Because you cannot easily determine what happens to polarity inside the box, their idea is that one orientation of the plug would result in less of an EMF being generated by the box. The little gizmo measures intensity of the magnetic field generated, and you change orientation of the plug at the wall to find out which way generates the least reading. I played with it long time back and did find on some of my components plug orientation really did produce markedly different readings on the Elfix. Other components it made no difference at all with plug orientation.

 

RE: Why would reversing AC leads reduce hum in a component?, posted on February 10, 2017 at 14:17:05
jea48
Audiophile

Posts: 6770
Joined: January 5, 2005
I would imagine the switch reverses the AC polarity to the primary winding of the power transformer. The correct AC polarity can have an affect on the SQ of piece of audio equipment.

Here is a quote from Charles Hansen:

1) Reversed AC polarity -- All power transformers have an inherent asymmetry to their construction. The primary winding comprises multiple layers, so that one lead is connected to the innermost windings and the other lead is connected to the outermost windings. This means that one lead has a higher coupling capacitance to the core of the transformer. Please remember that the AC supply is also asymmetrical, with the neutral lead essentially being at ground potential (assuming there is not a fault in the house wiring). The result is that one orientation will give a higher AC leakage current to the chassis of the amp (and worse sound) than the other orientation.

Not all transformer manufacturers use consistent markings on their transformers so that the correct orientation can be identified, and not all amp manufacturers pay attention to this even if the transformer is correctly marked. The result is that many audio products have a random chance of being correctly oriented. I would have to assume that the amp was modded to achieve the correct orientation, thereby achieving improved sound quality.


You will also see comments from John Curl.

 

RE: Why would reversing AC leads reduce hum in a component?, posted on February 10, 2017 at 16:09:31
Tre'
Industry Professional

Posts: 17263
Location: So. Cal.
Joined: February 9, 2002
"why would reversing the feed to the primary winding of the power transformer cause a safety issue?

In and of itself, it wouldn't but, if performed - as is often recommended - by reversing polarity at the mains input rather at than the transformer input, it very likely means (at least in the UK) that the fuse is in the neutral line, not the hot.
"

Correct. We would want to reverse the leads feeding to the primary of the power transformer after the fuse so the "Hot" is always fused.


Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Or for the more experienced..., posted on February 11, 2017 at 05:08:36
"That is not quite the principal the Elfix works on..........Because you cannot easily determine what happens to polarity inside the box,"
Is it weird science then? I tried to do a search to see what principles is does adhere to but was not successful.
My voltmeter is pretty straightforward with polarity.

 

RE: Or for the more experienced..., posted on February 11, 2017 at 08:40:36
Sondek
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Out of curiosity I dug my Elfix outta the drawer to see if there was some better explanation of the theory of operation in the user instructions. Unfortunately no luck. Just basic how to use info. Although, they do say that does exactly the same thing as the Namiki Direction Finder, but for a lot less money. I did a google on Namiki, but could not find anymore explanation of its operational premise than the Elfix. I've had this thing for probably 20 years. When I bought it seemed like possibly useful tool, however it turned out to be more of a novelty item than tool. Once you know, according to it, what proper orientation is, the Elfix is useless. At best a one-time use.

 

All true in the perfect world of today., posted on February 11, 2017 at 08:45:55
jea48
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Posts: 6770
Joined: January 5, 2005
But what about two wire power cord and plug vintage audio equipment made before the polarized plug? The user has a 50/50 chance of plugging the plug into the receptacle so the equipment overcurrent fuse is on the hot conductor.

It should be mentioned on old 2 wire cord and plug equipment in the event of an overload the fuse is still in series with the load and will blow if the load exceeds the ampere rating of the fuse regardless if the fuse is on the hot or the neutral incoming power lines.

With a 3 wire power cord and 3 wire grounding type plug it could prove dangerous to the user as well as the equipment if the AC power polarity is reversed ahead of the fuse on equipment where the safety equipment ground from the wall receptacle is used.

What about the incorrectly wired wall receptacle where the hot and neutral wires are reversed?

What about the aftermarket power cord that has the hot and neutral reversed at the female IEC connector? This is more common than you would expect. Any one that buys non safety Listed aftermarket power cords should always test the cords to make sure the AC polarity is correct.

 

RE: Why would reversing AC leads reduce hum in a component?, posted on February 11, 2017 at 10:32:08
Tre, if the hot wasn't fused wouldn't it blow anyway with over current? Thanks, T456

 

RE: All true in the perfect world of today., posted on February 11, 2017 at 10:59:57
Ryelands
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All true in the perfect world of today

IIRC, fuses were being used in telegraphy by the 1870s and in electrical circuits by the early 20th century. IMHO, far from being of today's perfect world, they're pretty much obsolete but that's another topic.

But what about two wire power cord and plug vintage audio equipment made before the polarized plug?

Can't off-hand comment on old kit or US rules. IIRC, UK regulations have stipulated 3-pin plugs for pretty much everything other than lighting circuits since the 1930s except for what we now call 'double insulated' devices. (What domestic users did was of course a different matter.)

In the event of an overload the fuse is still in series with the load and will blow if the load exceeds the ampere rating of the fuse

The fuse will blow (sooner or later, often considerably later) but, if the fuse is in the neutral line, the circuit remains live and thus possibly hazardous, esp if the earthing is poor.

With a 3 wire power cord . . . it could prove dangerous to the user . . . if the AC power polarity is reversed ahead of the fuse on equipment where the safety equipment ground from the wall receptacle is used.

You're right - but isn't that where I came in?

What about the incorrectly wired wall receptacle where the hot and neutral wires are reversed?

Competent electricians do not reverse polarities for well understood reasons. Incompetent electricians can be lethal.

What about the aftermarket power cord that has the hot and neutral reversed at the female IEC connector? This is more common than you would expect.

I've never bought an audio-style after-market power cord but if I did and found it was wired incorrectly I'd make the mother of a fuss.

D

 

RE: Why would reversing AC leads reduce hum in a component?, posted on February 11, 2017 at 13:02:45
Tre'
Industry Professional

Posts: 17263
Location: So. Cal.
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Yes but you would have a blown fuse and there would still be 120vac in the chassis beyond the fuse holder.

Of course anyone opening the chassis without unplugging the unit first is an idiot.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Why would reversing AC leads reduce hum in a component?, posted on February 11, 2017 at 13:57:13
Ryelands
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Posts: 1867
Location: Scotland
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Of course anyone opening the chassis without unplugging the unit first is an idiot

That may well true but, if the fault puts hazardous voltages on the case and the earthing is imperfect (as with, say, an elderly amplifier with loose, rusted earth connections in which a 25-year-old capacitor has just failed), you'd need to be pretty savvy to avoid getting a shock.

Besides, wiring regulations are there as much to protect the idiot as the expert. Which I think is a good thing because we all do idiotic things from time to time.

Well, I know I did in my career even though I used to remind myself that almost every line in the Regs (US, "code") had cost somebody's life.

D

 

RE: All true in the perfect world of today., posted on February 11, 2017 at 14:21:47
jea48
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Posts: 6770
Joined: January 5, 2005
Can't off-hand comment on old kit or US rules. IIRC, UK regulations have stipulated 3-pin plugs for pretty much everything other than lighting circuits since the 1930s except for what we now call 'double insulated' devices. (What domestic users did was of course a different matter.)

Interesting to lean that all the mass produced audio equipment manufactured in the 1970s for sale in the UK had a 3 wire cord and 3 wire grounding type plug.

Marantz, Pioneer, Sansui, Kenwood, NAD, Nakamichi, Teac, Technics, AKAI, JVC, you name it, sold in the USA and Canada came with a 2 wire power cord and plug.

 

RE: All true in the perfect world of today., posted on February 11, 2017 at 15:38:17
Ryelands
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Posts: 1867
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Interesting to lean that all the mass produced audio equipment manufactured in the 1970s for sale in the UK had a 3 wire cord and 3 wire grounding type plug.

I never suggested such kit came with a 3-wire cord or a "3 wire grounding type plug" (whatever that is). I wonder if you know what "double insulated" means.

In fairness, your confusion may have arisen because appliances sold in the UK with two-wire cords do nowadays come with a three-pin plug though the "earth" pin is unconnected and typically plastic. There are valid reasons for that but they are not relevant here; I'd hate to add to your muddle.

The rest of your post was not worth the effect to respond.

If, as I assume, you meant "effort", I know how you feel.

D

 

RE: Why would reversing AC leads reduce hum in a component?, posted on February 11, 2017 at 18:20:16
jea48
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Posts: 6770
Joined: January 5, 2005
Ryelands said:
I never suggested such kit came with a 3-wire cord or a "3 wire grounding type plug" (whatever that is).

Really?

Ryelands said:
Can't off-hand comment on old kit or US rules. IIRC, UK regulations have stipulated 3-pin plugs for pretty much everything other than lighting circuits since the 1930s except for what we now call 'double insulated' devices. (What domestic users did was of course a different matter.)


A 3 wire type grounding plug is a plug that has 2 line prongs and a safety equipment ground prong/pin. In the case of a standard NEMA 5-15P 120V 15 amp plug a straight blade for the HOT, a straight blade for the neutral, and a round pin for the safety equipment ground. A wider neutral blade is not needed on a 3 wire plug because the ground prong/pin keys the plug so it will only plug into the mating receptacle in one direction.

Ryelands said:
I wonder if you know what "double insulated" means.


As matter of fact I do. And I also know double insulated power wiring for audio as well as video equipment did not exist in the 1970s, let alone earlier.

Ryelands said:
In fairness, your confusion may have arisen because appliances sold in the UK with two-wire cords do nowadays come with a three-pin plug though the "earth" pin is unconnected and typically plastic. There are valid reasons for that but they are not relevant here; I'd hate to add to your muddle.


LOL, fairness?

I would imagine the dummy ground pin is there so the plug can only be plugged in only in one direction. It's used to maintain plug to receptacle polarity orientation.

In the USA we don't waste the extra money on dummy ground pins. UL, NEMA, NEC, dictates 2 wire plugs must be polarized. They will only plug into a mating polarized receptacle in one direction. The neutral blade is slightly wider than the hot blade. In the USA it is against electrical safety standards as well as codes to install a 3 wire grounding type plug on a 2 wire cord. It's an electrical safety thing.

//

jea48 deleted from post prior to Ryelands response:
The rest of your post was not worth the effect to respond.

Ryelands said:
If, as I assume, you meant "effort", I know how you feel.

No, I doubt if you do.

Hind sites 20/20. I should have left it in the original message.


Best regards.

 

RE: Why would reversing AC leads reduce hum in a component?, posted on February 11, 2017 at 18:56:32
Ryelands
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Posts: 1867
Location: Scotland
Joined: January 9, 2009
You're talking nonsense about the UK system and its 3-pin plugs. No point in pursuing either it or what is meant by "double insulated". I'm sure you're right about US practice.

Whatever, I trust we can agree that the use of "cheater" plugs and the like to reverse the polarity of transformer primary windings is unacceptable other than as a temporary measure in competent hands. To suggest otherwise in a hobbyist forum is, well, ill advised.

D

 

RE: All true in the perfect world of today., posted on February 11, 2017 at 21:32:56
jea48
Audiophile

Posts: 6770
Joined: January 5, 2005
Ryelands said:
I never suggested such kit came with a 3-wire cord or a "3 wire grounding type plug" (whatever that is).

Really?

Ryelands said:
Can't off-hand comment on old kit or US rules. IIRC, UK regulations have stipulated 3-pin plugs for pretty much everything other than lighting circuits since the 1930s except for what we now call 'double insulated' devices. (What domestic users did was of course a different matter.)


A 3 wire type grounding plug is a plug that has 2 line prongs and a safety equipment ground prong/pin. In the case of a standard NEMA 5-15P 120V 15 amp plug a straight blade for the HOT, a straight blade for the neutral, and a round pin for the safety equipment ground. A wider neutral blade is not needed on a 3 wire plug because the ground prong/pin keys the plug so it will only plug into the mating receptacle in one direction.

Ryelands said:
I wonder if you know what "double insulated" means.


As matter of fact I do. And I also know double insulated power wiring for audio as well as video equipment did not exist in the 1970s, let alone earlier.

Ryelands said:
In fairness, your confusion may have arisen because appliances sold in the UK with two-wire cords do nowadays come with a three-pin plug though the "earth" pin is unconnected and typically plastic. There are valid reasons for that but they are not relevant here; I'd hate to add to your muddle.


LOL, fairness?

I would imagine the dummy ground pin is there so the plug can only be plugged in only in one direction. It's used to maintain plug to receptacle polarity orientation.

In the USA we don't waste the extra money on dummy ground pins. UL, NEMA, NEC, dictates 2 wire plugs must be polarized. They will only plug into a mating polarized receptacle in one direction. The neutral blade is slightly wider than the hot blade. In the USA it is against electrical safety standards as well as codes to install a 3 wire grounding type plug on a 2 wire cord. It's an electrical safety thing.

//

jea48 deleted from post prior to Ryelands response:
The rest of your post was not worth the effect to respond.

Ryelands said:
If, as I assume, you meant "effort", I know how you feel.

No, I doubt if you do.

Hind sites 20/20. I should have left it in the original message.


Best regards.

 

RE: Why would reversing AC leads reduce hum in a component?, posted on February 11, 2017 at 21:33:23
jea48
Audiophile

Posts: 6770
Joined: January 5, 2005

You're talking nonsense about the UK system and its 3-pin plugs.

Really? Why don't you enlighten the class with your vast electrical knowledge.

I would love hear your thoughts on why in the UK the 2 conductor power cord of a double insulated Class II piece of equipment or appliance uses a 3 wire grounding type plug as you have said.
Could it possibly be the reason I gave in my last post? The ground prong on the plug only allows the plug to be plugged into the receptacle one way. It maintains the proper AC polarity orientation of the plug to the AC polarity of the receptacle.Surely you understand that?



No point in pursuing either it or what is meant by "double insulated".

What do you think "double insulated" means?


Class II
Class II symbol

A Class II or double insulated electrical appliance is one which has been designed in such a way that it does not require a safety connection to electrical earth (ground).

The basic requirement is that no single failure can result in dangerous voltage becoming exposed so that it might cause an electric shock and that this is achieved without relying on an earthed metal casing. This is usually achieved at least in part by having at least two layers of insulating material between live parts and the user, or by using reinforced insulation.

In Europe, a double insulated appliance must be labelled Class II or double insulated or bear the double insulation symbol (a square inside another square).

https://en.wikipedia.org/wiki/Appliance_classes

 

Well I tried an experiment, posted on February 11, 2017 at 23:43:01
jedrider
Audiophile

Posts: 15154
Location: No. California
Joined: December 26, 2003
I got a cheater plug and snipped off the expansion tabs (easy to do but newer ones are wider the entire length, so that would be more difficult to snip) and tried reversing AC polarity.

I seem to get a 6-12 dB reduction in noise level. Just guessing, but I wonder how I would measure this with a scope??

So I listen to say Spanish guitar because it's usually on the quiet side and crank the volume louder than I normally listen and then remove the needle from the record and I can hear the hum. It seems lower when polarity is reversed AND the music sounds better. In fact, now it sounds better at the higher volume which is exactly where I want to be.

So I will open the unit up and reverse the primary leads. Note that the power supply is DIY and the primary leads look identical otherwise. I think I will tag the one that is suppose to be hot.

 

RE: Why would reversing AC leads reduce hum in a component?, posted on February 12, 2017 at 06:35:40
Ryelands
Audiophile

Posts: 1867
Location: Scotland
Joined: January 9, 2009
Why don't you enlighten the class with your vast electrical knowledge.

Because I've no idea if anyone else cares to know, because you're clearly out to score points, not to debate and because it's wandering off the OP's point.

But, if you go to http://www.acoustica.org.uk/ and scroll down to "UK Mains plug fuses", you'll find as clear an explanation as you're likely to find. Meanwhile, NB that:

* The use of unearthed but insulated devices long predates current definitions and standards which was why I wrote "except for what we now call 'double insulated' devices".

* The socket pictured in your link doesn't show shutters though the text describes them.

* It's inaccurate to suggest that "Type G wall sockets almost always include switches for extra safety". The switch is for convenience, not safety.

* Also inaccurate is "The lack of such an earth pin on a type C plug makes it impossible to connect it to a type G receptacle". Fused adapters (usually 1 or 2.5 amp) that make type C plugs perfectly safe in UK sockets are readily available.

And so on.

 

That's a good plan. (nt), posted on February 12, 2017 at 09:05:08
Tre'
Industry Professional

Posts: 17263
Location: So. Cal.
Joined: February 9, 2002
.
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Why would reversing AC leads reduce hum in a component?, posted on February 12, 2017 at 10:26:16
jea48
Audiophile

Posts: 6770
Joined: January 5, 2005
I did answer the OP's question. Your posts are the reason for our back and forth discussions. I suggest you should reread the OP's posted message again.



My response to the OP:

I would imagine the switch reverses the AC polarity to the primary winding of the power transformer. The correct AC polarity can have an affect on the SQ of piece of audio equipment.



Here is a quote from Charles Hansen:

1) Reversed AC polarity -- All power transformers have an inherent asymmetry to their construction. The primary winding comprises multiple layers, so that one lead is connected to the innermost windings and the other lead is connected to the outermost windings. This means that one lead has a higher coupling capacitance to the core of the transformer. Please remember that the AC supply is also asymmetrical, with the neutral lead essentially being at ground potential (assuming there is not a fault in the house wiring). The result is that one orientation will give a higher AC leakage current to the chassis of the amp (and worse sound) than the other orientation.

Not all transformer manufacturers use consistent markings on their transformers so that the correct orientation can be identified, and not all amp manufacturers pay attention to this even if the transformer is correctly marked. The result is that many audio products have a random chance of being correctly oriented. I would have to assume that the amp was modded to achieve the correct orientation, thereby achieving improved sound quality.


You will also see comments from John Curl.

http://www.audioasylum.com/audio/general/messages/449743.html


//

Ryelands said:
* The use of unearthed but insulated devices long predates current definitions and standards which was why I wrote "except for what we now call 'double insulated' devices".

We have already beat that horse to death. Audio equipment manufactured in the 1970s, and earlier, sold in the USA and Canada was manufactures with a captive 2 wire power cord and a 2 wire non polarized plug. The internal AC power wiring back then was not doubled insulated. You are just trying to change, or maybe clarify, what you said in previous posts on the subject.

Ryelands said:
* The socket pictured in your link doesn't show shutters though the text describes them.

* It's inaccurate to suggest that "Type G wall sockets almost always include switches for extra safety". The switch is for convenience, not safety.


What? All I wanted to know is the picture in the Link I provided look like the 3 wire receptacle and 3 wire plug used in a residential dwelling unit in the UK. You were the one that brought up the subject of the UK 3 wire receptacle and the use of equipment/appliances that use a 2 wire power cord using a 3 wire plug on the 2 wire cord.

Ryelands said:
* Also inaccurate is "The lack of such an earth pin on a type C plug makes it impossible to connect it to a type G receptacle". Fused adapters (usually 1 or 2.5 amp) that make type C plugs perfectly safe in UK sockets are readily available.


Type C plug? Where in any of your responses did you ever mention any plug other than a 3 wire plug?


////////


Here is the bottom line. IN the USA or Canada anyone that has a piece of vintage audio equipment with a captive 2 wire power cord with a non polarized plug you have a 50/50 chance, when plugging the unit into the AC power receptacle, having the proper AC polarity orientation correct feeding the primary winding of the power transformer of the piece of equipment.

You can easily check for the proper polarity plug orientation with a multimeter.

1) Disconnect all ICs from the inputs of the piece of equipment to be tested.

2) Set the multimeter to auto AC volts or a range above 125V (USA or Canada)

3) Power up the piece of equipment.

4) Touch one test lead probe of the meter to the metal chassis of the equipment.

Touch the other test lead probe of the meter to the equipment ground contact of the power receptacle. (If the receptacle is an old 2 wire non grounding type receptacle use the neutral contact of the other receptacle of the duplex outlet. The actual reference point for the test is the Grounded Conductor, the neutral conductor.)

Note the voltage reading.

5) Turn off the piece of equipment. Unplug it from the AC power receptacle. Reverse the plug 180 degrees and plug it back in.
*If the equipment is a power amp you might want to allow a few minutes to pass for the electrolytic caps in the power supply to bleed off before turning the equipment back on.

6) Power up the equipment. Repeat procedure 4). Note the voltage reading. The lower voltage of the two tests is the proper AC polarity plug orientation. Mark, identify, one side of the plug. Best place is on the neutral blade/contact side.

 

RE: Well I tried an experiment, posted on February 12, 2017 at 11:04:53
jea48
Audiophile

Posts: 6770
Joined: January 5, 2005
Sounds good!

I seem to get a 6-12 dB reduction in noise level. Just guessing, but I wonder how I would measure this with a scope??



You can easily check for the proper polarity orientation with a multimeter.

1) Disconnect all ICs from the inputs of the piece of equipment to be tested.
Equipment safety ground must also be lifted from the piece of equipment. As you did with the ground cheater.)

2) Set the multimeter to auto AC volts or a range above 125V (USA or Canada)

3) Power up the piece of equipment.

4) Touch one test lead probe of the meter to the metal chassis of the equipment.

Touch the other test lead probe of the meter to the equipment ground contact of the power receptacle. (If the receptacle is an old 2 wire non grounding type receptacle use the neutral contact of the other receptacle of the duplex outlet. The actual reference point for the test is the Grounded Conductor, the neutral conductor.)

Note the voltage reading.

5) Turn off the piece of equipment. Unplug it from the AC power receptacle. Reverse the plug 180 degrees and plug it back in.


6) Power up the equipment. Repeat procedure 4). Note the voltage reading. The lower voltage reading of the two tests is the proper AC polarity orientation.

 

Thanks -- My Bad, posted on February 12, 2017 at 19:35:33
jedrider
Audiophile

Posts: 15154
Location: No. California
Joined: December 26, 2003
I assumed that it didn't make a difference, because I've seen many transformers with two black primaries. This toroidal had a white and a black! I found that in both cases I had wired the transformer wrong in both my phono stage and in my headphone amplifier.

Corrected it and sounds much, much better.

Thanks.

 

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