Determining polarity of A/C line plugs

radio, tape, stands and accessories
vinylrayk
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Re: Determining polarity of A/C line plugs

Post by vinylrayk » 22 Apr 2019 17:28

Alec124c41 wrote:
14 Mar 2019 20:06
I plug the component in, then lightly run a finger across the faceplate. Ine way gives a slight tingling sensation, the other none. Go with none.

Cheers,
Alec
At last!
Something that would surely be detectable on a double-blind test.
Did you feel any desire to hum when you did this? :D

Ray K

ChrisfromRI
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Re: Determining polarity of A/C line plugs

Post by ChrisfromRI » 22 Apr 2019 17:37

Jim Leach wrote:
22 Apr 2019 16:59
@chrisfromri this is exactly where I was going.

It seems they take the AC straight to the transformer and the output is then rectified. So in theory, it doesn’t matter, but I may swap to modern (polarized) 2-prong or three prong cords once I do your test.

Based on how it’s wired, unless there is internal leakage on the transformer, the metal chassis is “floating”. But I can do the testing easily enough.
You're absolutely right Jim. The other problem I have found is that it is well documented which blade of the modern 2 prong plug is wider and which side of the modern electrical wall outlet takes the wider blade - the Neutral side of the AC line. Look inside an electrical service panel and you will see that the Neutral is bonded to Ground inside the panel. You end up getting your service Ground and Neutral on the fat blade. That great that there is a standard for wiring in the house that is regularly applied.

Unfortunately, inside the piece of electronics there isn't a standard being regularly applied, or only being applied in a very lax manner, as to which of the two AC connections (Neutral and Hot) goes where inside the piece of electronics. As you aptly point out there are often issues with transformer winding leakage, and there are center tapped transformers with unevenly wound coils. The only way you really ever know how to get the lowest chassis potential to electrical ground is as I laid out above.

I can't tell you how many times I had a friend complain to me about a hum when using a new expensive phono stage, and I asked if that phono stage had a 3 prong plug (and IEC chassis connector). When they told me yes, I suggested tying a 2 to 3 prong adapter at the wall end to simply lift the third wire, and in almost every case their hum vanished.

In the "old days" the 2 prong plugs weren't polarized and you could easily flip them back and forth. Namiki and others even sold devices (called Direction Finders) for audiophiles back 30 years ago to allow you to tell which way to plug your electronics plug in. Those of us in the know would simply keep that money to buy more records with, and break out our VOM because we understood what the specialized device was indicating). Now the polarized blades, prevalence of 3 prong plugs and the lack of attention to the standard being applied INSIDE the electronics, and the lack of attention by audiophiles to this detail, can allow the system noise floor to creep up in many audio systems.

Alec124c41
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Re: Determining polarity of A/C line plugs

Post by Alec124c41 » 22 Apr 2019 21:51

vinylrayk wrote:
22 Apr 2019 17:28
Alec124c41 wrote:
14 Mar 2019 20:06
I plug the component in, then lightly run a finger across the faceplate. Ine way gives a slight tingling sensation, the other none. Go with none.

Cheers,
Alec
At last!
Something that would surely be detectable on a double-blind test.
Did you feel any desire to hum when you did this? :D

Ray K
Absolutely!

Cheers,
Alec

Jim Leach
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Re: Determining polarity of A/C line plugs

Post by Jim Leach » 23 Apr 2019 22:31

Thanks again Chris.

You and I are o the same page.

And I replaced all the outlets in my house so they are correctly wired. Unfortunately they used BX so the ground is on the steel jacket, rather than a copper lead... Once I'm back up and running I was planning an isolated ground (AKA "hospital" outlet) with a properly run additional ground lead to the buss bar in the panel as it should be.

ChrisfromRI
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Re: Determining polarity of A/C line plugs

Post by ChrisfromRI » 24 Apr 2019 02:02

Thanks Jim. Replacing and checking all of the outlets with an LED tester is huge. BX cable is a challenge for the ground quality but does give some shielding.

For my dedicated 2 channel audio room I ran a dedicated run of #12 Romex from a 20 Amp Breaker in the service entry panel to a single 20 Amp Outlet in the audio room. All of my electronics outlet strips plug into that one outlet. An extra advantage is that when there is a lightning storm I just pull one plug. I have a surge suppressor in the service entry panel and another in the dedicated audio outlet for protection when not home. I thankfully also have the benefit of being the only home on the secondary pole transformer, which affords extra electrical isolation from neighbors.