Audio is one of those hobbies that have many empirical indicators. Things like type of solder, soldering technique, and which way a components plug is plugged in can make a difference depending on the component.
>>"I've just noticed that from experimenting with preterminated factory builty cords that not all companies use the same polarities. Even with two stock cords, one from USA made in China and one from China made in China for USA the polarity of the cords are reversed."<<
Just one of the problems with after market power cables. Very few if any are UL listed.http://www.marchansen.com/tn102/
Reversed AC polarity can cause noise and hum from your audio system as well as effecting it's sonics.http://forum.audiogon.com/cgi-bin/fr.pl?htech&1014011751&openmine&zz
Yes. Depending on the resolving level of your system the individual components of your system will have different sonics depending on the orientation of the ac plugs. Experiment with each component to determine which orientation sounds best to you and mark the plug for future reference. When manufacturers make a component little consideration if any is given to plug polarity. It is of low priority to them.
>>"When manufacturers make a component little consideration if any is given to plug polarity. It is of low priority to them.'<<
For the big boys it's very important. Hi-end equipment manufactures of today test the power transformer/s for the correct primary winding to secondary winding polarity.
Van Den Hul make a Polarity Checker. A small pen shaped digital meter.
You can also check all your components and plugs for correct polarity with a simple test meter.
Instructions from the Chesky website:
By Michael Trei
One simple tweak that many people tend to ignore, is to be sure that each piece of gear is plugged into the power outlet using the proper polarity. The power supply transformer in every piece of gear will leak a little current to the component's chassis, and in most cases, you'll get better sound if this leakage is minimized by observing the proper A/C plug orientation.
A few decades ago, audio gear had simple two prong A/C plugs that could be inserted in the socket either way, but now all plugs are polarized so that they only go in one way. To get around this, we need to use a simple adapter called a cheater plug, available for a buck or so at any hardware store. The cheater has two narrow prongs that allow you to use it in the socket either way, and cheaters will also take a three prong plug with a ground pin, replacing the ground prong with a metal tab or wire that you can connect to the center screw on the outlet plate. If you want to reverse a three prong plug, you'll want the version that uses a wire so that you can still connect the ground with the plug in the reversed position.
While there are fancy polarity checkers that you can buy from companies like Van den Hul, the same tests can be done using a simple inexpensive digital voltmeter. First, disconnect all of the cables except the power cord from the component that you want to check, as any connection to other gear can throw off the results by providing multiple grounds. Then plug in the component using the normal orientation, but with the cheater plug in place. If the component uses a grounded cord, make sure to connect the green ground wire on the cheater plug to the outlet plate screw. Turn the component on, and set the voltmeter to A/C volts. I usually simply pinch one probe between the fingers of my left hand, then I hold the other probe in my right hand and touch the tip to a metal part of the component's casework such as a cover screw. Note the reading in volts. Turn off the component, reverse the plug in the wall outlet, turn the component on again and check the voltage once more at the same point on the case. If you got a lower reading this way, leave the component plugged in as it is, otherwise remove the cheater and plug it in normally.
If you repeat this test for each component, you should hear cleaner, more transparent high frequencies, and a lower overall noise floor. Total outlay? About five bucks. OK, $25 if you need to buy the multimeter, but still a bargain.
I have found that polarity is important. To my ears, when the polarity is wrong, the bass is dramatically reduced, soundstage shrinks, and midrange is less focussed. Listen to something with good bass that you're familiar with. The best bass response will probably be the right plug phase.
Huh?! In the USA, the small blade should be "hot", and the large blade should be "neutral"...end of story!
Jeff's explanation is correct, except that cheater plugs now only come polarized (one wide blade) so if you want to use them as he describes, you'll have to file down the wide blade so it wil go into the socket either way.
Then plug in the component using the normal orientation, but with the cheater plug in place. If the component uses a grounded cord, make sure to connect the green ground wire on the cheater plug to the outlet plate screw. Turn the component on, and set the voltmeter to A/C volts.
>>"If the component uses a grounded cord, make sure to connect the green ground wire on the cheater plug to the outlet plate screw."<<
Jeff I think you meant to say here, *do not*, connect the ground wire for the test. The equipment needs to be free of all earth grounds for the test. Infact if the type of ground cheater used is the brass or copper strap type, tape or cut off the ground strap so it does not come into contact with the receptacle cover plate screw. The screw is connected to the equipment grounding conductor. The reason the audio equipment must be isolated from earth ground is not because of the earth ground its self, it is because the equipment grounding conductor and the neutral conductor, (the grounded conductor), are connected together at the main electrical service panel neutral/ground bar.
Munufactures usually check to make sure they have properly wired the power supply's transformer primary correctly, sometimes they miss one.
Another cause of reverse AC 120V polarity is after market power cords. Either the male plug or IEC female connector wiring is reversed. If you are using after market power cords check them for proper continuity, polarity.
If the amp is pluged into one electrical outlet and the preamp in another, sometimes the polarity is reversed at the receptacle. Check for proper receptacle polarity.
If it turns out one of your components power transformer primary winding was connected with reverse polarity and you are using an after market power cord just reverse the hot and neutral conductors at one end only. The male plug, or IEC connector end. Repeat the polarity test with the ground cheater to verify it is correct.
This test will work for a preamp or power amp. For newer two wire cord and plug equipment such as DVD or CDP players this test procedure may not work. The case, enclosure, of the unit is floating and has no electrical continuity with the electrical power supply or electrical components inside the enclosure. Another thing about CDPs and DVD/SACD/DVDA players is the fact they use multiple power supplies.
Of course if you decide to use a balanced power unit, all this is of no concern.
>>"Of course if you decide to use a balanced power unit, all this is of no concern."<<
Maybe, True if all the audio equipment connected by ics is pluged into the same balanced power unit.
Nsgarch, What is your thoughts of feeding a balanced power unit from 120V? Jmho, I believe there would be better isolation if a balanced power unit was feed by 240 volt.
Here is some reading material. Make note of how the utility companies bond the high voltage neutral and all the secondary neutrals together at every utility transformer.
This can't be good for AC noise.... http://www.mikeholt.com/documents/strayvoltage/pdf/DangersofStrayVoltageandCurrent.pdf
Jmo it appears to me the only way to get total AC isolation is with an isolation transformer fed from 240 volt.
Nsgarch, I am not sure.....
>>"Of course if you decide to use a balanced power unit, all this is of no concern."<<
>>'Maybe, True if all the audio equipment connected by ics is pluged into the same balanced power unit."<<
After thinking about the balanced 120V (60V-0V-60V) system I am not sure one would not be in the same boat.
It's those darn ICs that connect the audio equipment together.
Two hot 120 volt conductors.
I will call them L1 and L2, 120V.
A power transformer, for say, a power amp.
It is nothing more than an isolation transformer. It has a winding polarity relationship between the primary and secondary windings.
For sake of argument lets label the primary leads H1 and H2. The secondary leads X1 and X2. If the manufacture of the transformer labeled the leads correctly, H1 polarity match is X1 and H2 polarity match is X2.
Connect the audio power transformer primary to the 120V power from the balanced power unit.
(L1 to H1) (L2 to H2). If all the audio equipment power transformers are wired the same the the secondary AC polarities will be the same and so the DC power supplies. (Providing a primary winding polarity to power supply polarity were correct to start with)
What happens if one of the audio equipment power transformer's primary connections is reversed?
(L1 to H2) (L2 to H1)
Jea, a 240V line is inherently "balanced". Its ground and neutral are the same (center) conductor, with a potential of +120v on one side and -120V on the other (which reverses every 60 sec. of course.) BTW, I don't believe European 240V power is configured this way (at the outlet), but somebody correct me if this is wrong.
Now to get balanced 120V is a whole 'nuther matter. First you get a great big toroidal transformer and feed it 120V +/_ into one tap and zero volts (neutral) into the other. In a second, identical winding, you take the power out at 60V +/_ tap and 60V -/+ tap and feed one to each blade of the AC plug. To keep the drama queens at U/L happy, you create an artificial ground/neutral for the center ground pin of the plug/receptacle. This is done through some kind of circuitry which U/L is willing to certify provides shock protection ;~)) but it's not an "earth" ground.
If your equipment circuit designer or assembler has been less than attentive as you postulate, then balanced power will save his/her ass because both primary leads are being fed equal (60V) voltage in a "push-pull" arrangement around (or across) an "imaginary" ground (rather than the normal zero volts in one lead and plus-or-minus 120V in the other.) So in the balanced-power-fed component, circuit polarity relative to ground disappears along with any polarity mismatches in the wiring.
>>" a 240V line is inherently "balanced". Its ground and neutral are the same (center) conductor, with a potential of +120v on one side and -120V on the other"<<
Correct. The utility transformer's secondary windings are configured as a split phase winding exactly a balanced power system. 120V-0V-120V. The center point of the two connected secondary windings is bonded, connected to earth ground. Just like the 60V-0V-60V system. If all the loads connected to the 120V-0V-120V utility transformer were all 240V loads it would work exactly like the 60V-0V-60V balanced system.
Here is one for you. For a single phase/split phase utility
transformer where 120 volts loads are exactly balanced across the two mains, zerro amperes will travel back on the neutral conductor to the source, the transformer. Example 30 amps of connected 120 volt load from L1 to neutral, and 30 amps of connected 120 volt load from L2 to neutral.
The connected 120V loads from L1 to neutral will be in series with the connected 120V loads from L2 to neutral. Only the unbalanced 120V loads travel back on the neutral conductor to the source, utility transformer.http://www.ibiblio.org/obp/electricCircuits/AC/AC_10.html#xtocid269100
I don't know why your power cords would be reversed, but to meet current NEC codes, they have to be polarized the the right way. For your basic 115 V three prong cable, the big one is earth, the wide one is neutral, and the smallest one is the hot or line.
Now that being said, there are some older cords which are not polarized correctly, as they were made long before polarity for line cords was written into the NEC. The thing is, I am pretty sure by the time the IEC connector came along, polarity had been in the code for a while. I do believe this was the reason the IEC connector was adopted. I am writing this from memory; I don't have a history of NEC at my disposal.
I suggest you pitch the incorrect polarity power cords. If you are in doubt about which one is correct, go to your local hardware store and buy a Belden cord for about 7 bucks or so. This will be correct; compare everything to this and toss the ones which are polarized opposite.
You can check your wall outlets in your house/apt easily enough: when you are the hardware store, pick up a line polarity tester for around 5 dollars or so. On this are a series of LEDs which light up depending on what is wrong. You can get expensive and blow up to 10 bucks on one if you want to also check the GFI outlets in your kitchen or bathroom, but you won't need GFI testing for your stereo stuff.
By the way, if one of the cables you find is polarized backwards and it has a UL sticker on it, please call your local UL office, they are in the phone book. I am SURE they will be MOST interested!
Am I missing something?
Typically, AC is fed into a components isolation transformer, through full rectification and large filter/storage capacitor networks accross the secondary outputs, thus producing DC voltage. This, intern, feeds all the DC circuits typically isolated from their metal chassis (circuit depedant). Why does it matter which AC polarity feeds the transformer? Isn't DC is the final product?
In Jeff's artical, "all transformers will leak a little current to the component's chassis". Shouldn't it be "leak inductance" or "capacitance"? With lots of chassis made from aluminum, where's the stray field interaction with sensitive circuits, etc.? Most audio components isolate their audio I/O connectors from the chassis, thus minimizing ground loop potential between components with grounded chassis. Any minute stray voltages that do develope along steel chassis, doesn't default into audible subjectiveness.
Any helpfull explanations?
Metro04, you are correct in your basic evaluation of the situation, but yes, you are missing something, and that's the damn power company!
As the article Jea48 mentioned above illustrates, the power company uses (literally) the ground for its return leg to the generator. Which means in normal 120V house systems, the neutral blade is not always at zero potential relative to ground (in fact I've never found it to be so.)
So it's not the component's fault exactly, but depending how a components (power supply) circuits happen to be oriented to this "ground leak" current will mean slightly more or less noise (usually 60 cycle hum) in your system.
Balanced power units simply eliminate this problem altogether.
Thanks for getting back with me.
Even if the neutral wasn't at zero potential, most domestic voltges provide more than adequate supply for most component DC rails and regulated circuits (+/- 0.5 to 1.0 VAC of the localized incoming supply, which can swing pretty widely throughout the day, and per region).
In most homes, aren't the neutral and "ground" combined within the breaker box? This SHOULD place the N and G at the same potential, thus supplying the proper circuit voltage into the component's isolation x-former.
Now, what happens to so called "leakage inductance" within a non-ferrous chassis (aluminum)? What about components utilizing un-grounded chassis (2-prong cords), or a combination of the two? If none of the component's circuits are electrically grounded to the chassis, what are these stray voltages going to affect? In a ferrous chassis, I can see some 60 Hz magnet issues affecting certain circuits, but not with aluminum. Any minute x-former leakage would stay localized around itself. Right, or what?
I'm just concerned about blanket statements towards these wiring orientation claims, and whether they are indeed audible in most scenarios.
Your responces are always welcome, and I'm not trying to be argumentative. I do have lots of electronic background, but claim to know everything.
Metro, the answer to:
"In most homes, aren't the neutral and "ground" combined within the breaker box?"
Is no. And this is very important to understanding the "leakage" problem oulined in the article you cite above.
The neutral is zero relative to the 120V on each side of it. But it is not zero relative to earth ground.
So depending how the power supply in a component is laid out, connecting one of the two AC plug blades to neutral will result in less ground current leakage through the "neutral" leg of the power supply circuit. As a matter of fact, that is why, as someone described above how to measure for the best plug orientation, they specifically mentioned not to connect the ground pin of the AC plug when doing the measurement. To which I'll add two more rules: turn off the component, and disconnect all other connections to the component (ICs, spkr cables, coax cable or digital feeds, etc) because they may be connected to ground somewhere on their other ends, and you don't want that.
The idea behind this testing procedure is to "force" current that would,in grounded components, ordinarily drain to ground, instead to "leak" through the neutral so it can be measured. And then minimized by choosing the proper plug orientation.
So why is doing this a good thing? Because when everything is hooked back up, some current will drain to ground through the ground leg, and every one of these conditions in your system represents a ground loop which increases the baseline level of hum (and sometimes noise) in the system.
Here is a couple of posts from my thread on AA.
Pinging Bob Crump, Can you answer a question for me?
Posted by jea48 (A) on May 19, 2005 at 14:13:30
Bob, John Curl said in a reponse to this question to ask you. When you design and build a piece of equipment is there a set rule on the polarity of the power transformer? That is on the primary side of the transformer are the leads such that the neutral is always on an identified lead and the hot on an identified lead on the transformer. I ask because I have read old archives on Agon where some have talked about reversing the AC polarity feed to the unit, switch the hot and the neutral. Does it affect the sound as some have said? Also does the fact that the neutral is at ground potential have any bearing on the design of a piece of equipment?
Re: Pinging Bob Crump, Can you answer a question for me? - rcrump 14:27:42 05/19/05 (31)
In Reply to: Pinging Bob Crump, Can you answer a question for me? posted by jea48 on May 19, 2005 at 14:13:30:
>>"Yes this is very important or the bass and focus will be affected...........Put your red lead of a multimeter on chassis ground and the black lead on a decent earth ground, set the meter to ACV and measure the ground potential with the unit plugged in one way and then 180 degrees off (cheater plug) and make ACV readings each way......Gear being tested should be out of the system or readings will get confused.......The lowest reading will be the correct way of plugging in the unit.......Most transformers are marked for the hot side, but best to test them........"<<
Re: Pinging Bob Crump, Can you answer a question for me? - john curl 19:07:04 05/20/05 (0)
In Reply to: Re: Pinging Bob Crump, Can you answer a question for me? posted by jea48 on May 2, 2005 at 17:57:57:
">>Jim, like it or not, we have to test the transformers, as to how to wire the PRIMARY. NOT secondary."<<
Thank you for the informative response, and will look into it further. I did find some interesting articles after posting my last response, but still have inquiries pertaining to non-ferrous chassis having the same effect. Lots of veteran electronic engineers at my work, so I'll get to the bottom of this, yet.
First, there is no such thing as "zero volts," we just agree to call something zero (the earth) and measure everything relative to it. It is completely arbitrary.
Second, neutral and ground are bonded in the sevice panel and only there. Go to Home Depot and look at a panel. The neutral bar and the ground are bonded. Another term for neutral is grounded conductor.
Third, in a house, circuits are taken off each "hot" conductor, and the currents in the grounded conductors (which are all tied together) cancel each other out. In other words, if, by chance, the currents on each hot leg were exactly equal, the grounded conductor could be disconected from the service neutral (and the ground) and every thing would work. All the current would flow through the hot legs.
Fourth, the reason the grounded conductor measures hot relative to ground is because the conductor has resistance, and there is current flowing through it. Since there should be no current flowing in the ground, and the two are tied only at the panel, there will be a voltage difference at the outlet (but not at the panel).
Fifth, Mr. Holt does not mention, although I am sure he knows, that all power is generated and transmitted as three phase, each 120 degrees apart in time. When each phase has equal current, they sum to zero and there is no net current to flow through the ground. Any current is due to the three phases being unequal and will be small relative to the total current draw. If any significant power is disipated in the Earth, the power company loses money.
The Earth naturally has absolutely enormous currents flowing in it, making the Earth into a giant magnet.
Polarity is a safety issue.
>>"Fifth, Mr. Holt does not mention, although I am sure he knows, that all power is generated and transmitted as three phase, each 120 degrees apart in time. When each phase has equal current, they sum to zero and there is no net current to flow through the ground. Any current is due to the three phases being unequal and will be small relative to the total current draw. If any significant power is disipated in the Earth, the power company loses money."<<
>>"Mr. Holt does not mention"<<
The article was not written by Mr. Holt.
>>"When each phase has equal current, they sum to zero and there is no net current to flow through the ground."<<
In my neighborhood there is only one 7200V HV line on top of the power pole, feeding many pole mounted transformers. Lets say for argument, (A) phase of the 3PH 4W 7200/13200V wye feeder leaving the substation. No balance here....Just one ungrounded 7200V conductor and the grounded conductor, the neutral (single phase).... No balance in the (B) phase neighborhood or even the (C) phase neighborhood. I will grant you at the point where the 3PH 4W HV feeder branched out going their separate ways, from that point where the neutrals were joined to the main feeder neutral, back to the subtation the HV neutral only carries back the unbalanced load plus*....
Jea48, thanks for straightening me out. The author is Donald Zipse, and Mr. Holt reproduces the article. I should have been more careful.
I agree with your point about each neighborhood being on a different phase, but my point is that the net return current of the entire system is very small compared to the load.
While each neighborhood may be on its own phase, my third point still holds and the neutral current is relatively small.
Mr. Zipse's proposal (comparing fig. 21 and 22) is to remove the neutral-ground bond from the panel and replace it with a dedicated ground wire back to the transformer neutral-ground connection. One problem I can see with this approach is that if this new 4th ground conductor was damaged or the transformer ground missing or damaged, as far as the customer could tell, the system would function normally. It much easier to visually verify the neutral-ground bond at the panel than to vouch for the integrity of a 4th conductor to an off site ground.
I can appreciate the logical appeal of completely separating the neutral and the ground functions and wires. However the cost to implement would be huge, the benefit theoretical.
The author himself states that his proposal was "soundly rejected" by both the NESC and the NFPA.
>>"I agree with your point about each neighborhood being on a different phase, but my point is that the net return current of the entire system is very small compared to the load."<<
The current flowing in the neutral, (the grounded conductor), should be the same as the current flowing in the hot conductor for a single phase circuit. Current will take the least resistive path back to the source, but it will also travel in any other path provided back to the source. If every single utility xfmr's secondary neutral is bonded to earth there is a parallel path for current to flow also. Also at every utility transformer the secondary neutral is also bonded to the HV neutral and earth ground. Then per NEC every service neutral is bonded to earth ground by connecting to the metallic water system that is even a better least resistive path for current to travel back to the source than the earth. Also grounding electrode ground rods for neutral bonding.
>>"Mr. Zipse's proposal (comparing fig. 21 and 22) is to remove the neutral-ground bond from the panel and replace it with a dedicated ground wire back to the transformer neutral-ground connection."<<
The way I understood what MR. Zipse wants to do is feed the single phase utility xfmrs with two ungrounded feed conductors.
The utility companies want nothing to do with this though.
*Two HV bushing xfmrs.
*Additional high line and insulators.
*Additional high voltage cutout and fuse for feeding the HV primary of the xfmr.
* No more using the same conductor for the HV neutral and LV secondary neutral,(commonly done on multiple pole mounted, multiple xfmrs installations.
>>"The author himself states that his proposal was "soundly rejected" by both the NESC and the NFPA.'<<
Does that surprise you? It doesn't me.