Actually that was kind of uncalled for, if you look at the construction of the typical inexpensive EI or toroid power transformer you will discover that the leakage currents to chassis can be significantly higher in one connection orientation than in the other. (Split bobbin types generally do not exhibit this issue to the same degree) It's very easy to measure and those currents in a device with a 2 wire line cord will flow through the audio wiring to other components, and it can be subtly audible in some cases and can be measured as a degradation of the noise floor of that source component and possibly other devices that may sink the leakage currents.
In any event I think it is a good idea to figure out how which orientation minimizes leakage currents into the chassis as a matter of principle - in extreme cases it can be audible for a variety of reasons.
I have a Mitsubishi DA-F10 FM tuner that used to have a 2 wire non-polarized line cord. I installed it in my system and whenever it was plugged in my system hummed like crazy. Turned around the mains cord and the hum dropped by roughly 12dB or so - still not enough. Investigation revealed that the metal case of that tuner which was about 30cm above my 26DHT line stage was electro-statically coupling to the plates of those 26s. The solution turned out to be better shields on the tubes AND a 3 wire ground cord wired to minimize the effects of leakage current from the transformer primary. (case now at ac ground potential)
In 25 yrs of professional audio design I have come to take this issue seriously and always check for the transformer connection that results in the least leakage current. Allen's point about caps on the primary side to chassis is also well taken.
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No, I disagree. The primary is connected across the AC mains.
The AC mains outlet has two conductors (we ignore the safety ground) one of those is called "hot" the other is called "neutral". If you follow the nuetral wire back to the service entrance box where the main AC circuit breaker is loacted you find that the nuetral is bonded to the building's ground system. This system is ususal a 6 ft long copper rod driven into the ground and or some length of re-bar enbedded into a cast concrete foundation and so either of these are bonded to a cold water pipe.
The neutral wire carries return curent so there is voltage in on buy by buiklding code this is limited to (from memory) about 5% of the mains voltage but is typically half of that at most.
Bottom line is that one side of the power transformer's primary is connected to the building's ground system.
The amps chassis, if a three conductor power cord is used will be conected to safty ground. Back at the service entrance box the nuetral and safty ground are bonded.
The above describes US building code and is mostly uniform from state to state. But I think this also applies to most of the world
The thing to remember is that of the three holes in a standard 120 VAC mains outlet only one of them will get you a shock the other two are tied to Earth. At least in the USA.
Not always. For instance, I have an isolating step down transformer between the wall outlet and my amp (the amp is an ex-USA jukebox system and we are 230VAC so I need a step down).
Hence, the primary is floating.
In any case, while the difference as described probably can be measured, my question is is it ACTUALLY audible? Or is the perceived difference another of the many psycho-audiatory effects that we all suffer from when we experiment on and for ourselves?
Didn't the OP specify the condidtions? He said the PT was across mains. If that is not the case then the effect has moved from the PT to the isolation transformer. At some point you do have a transformer across mains AC.
But I also seriously doubt this makes any audible difference at all. Unles the audio has more or less AC "buzz" the e-field around an AC mains connected transformer might differ on polarity.
A good experiment that will prove existence of those psychological effects is to do an "A/B Test". with some listeners but use a flawed procedure where you tell them "now I will connect system A". and then tell then you are playing "system B" and switch back and forth giving good time to listen to both. But what you do NOT tell then is that there is only one system and you don't ever switch. Funny thing is that many people will prefer A over B or B over A.
I suspect this is what happened in this case.
Wow! So rude and so wrong.
OP is right. Connecting the end of the primary winding that's nearer the transformer core to "live" will result in a smaller capacitively coupled mains voltage in the secondary.
Who is going to enforce it if true? And, why would you not do it if there weren't a law?
Not that it is not a good idea, and I would not work on a piece of equipment without a 3 wire connection with ground.
Just saying laws are made by 'the machine'.
Sven
Not that it is not a good idea, and I would not work on a piece of equipment without a 3 wire connection with ground.
Just saying laws are made by 'the machine'.
Sven
Hello All,Hi,
I read that if you reverse your mains connections on a power Tx primary it changes the sound of CD players amps etc!
I have tried this and it gives a very slight change in the sound!
In the UK the mains supply has a live and neutral + earth. The neutral is at a very close potential to earth! So this is a possible thought!
The mains transformer has a start and end of the winding, so if you connect the live to the start of the winding as the coil comes to the end you have a shield of neutral connected windings at the end of the coil (shielding the live supply). If you connect the other way around you have the live on the outside of the winding! Ok torroids are self screening?
Is this the same in other countries?
Regards
M. Gregg
Sorting out the unwilling, unable and the uninformed is sometimes difficult. Today walking with a young engineer from my office through a new hospital facility we were doing a final inspection (we are mechanical engineers). On the wall there was an assortment of power outlets on the wall; white ones, red ones, orange ones. Wavebourn there is a law sort of, NFPA 70 (National Fire Protection Association 70) AKA National Electrical Code and in our case the California Electrical Code. The intent is not to kill anyone. The white ones are standard like in your home. The red ones are emergency (generator). The orange are isolated ground. What they have in common is that they have a hot conductor, a grounded current carrying conductor (neutral), and a safety or grounding conductor. The single word that describes the commonality is polarity.
Transformers also have polarity electrically and magnetically. Change the primary polarity does it make a difference? Yup. Change the secondary polarity does it make a difference yup? Electrolytic capacitors may even purge with a bang.
M Greg, if the polarity is kept consistent can the transformer tell which lead is connected to the neutral conductor in the wall? No it is not that smart. It is not about the transformer. It is about grounded, grounding, bonding and polarity.
DT
All just for fun!
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I tried this and now I'm hearing strains of "Nearer My Ground To Thee."
Be very careful - you could destroy a perfectly good flower bed.
What happens if you replace a power cord of an amp that was used by some rock Super Star, if it's proud current owner brought it to you to replace output tubes by matched quad stored in an attic of some castle during last forty five years?
There is a lot I do not know about sine waves and I am always willing to learn! However,
Fact: Your mains ability to transform is effected by harmonic distortion. I have seen sine waves that look like a sharks fin due to harmonics from DC drives in industry. That is why some people say my HIFI sounds better at different times of the day! This is so important that the supply authorities will stop a company installing any more DC drives if the harmonics cannot be removed with power factor correction!
Tx efficiency goes down also costs more to run the equipment!
Fact: Your primary of your mains Tx has one side closer to ground if it is connected to the mains supply! (One side is neutral)
Fact: All mains supplies have Radio Freq interference caused by switching outside in the "real world". Also if you have any power lines in the air they act like an Aerial and take it to your supply Tx. It sits on top of the sine wave with all the transients and spikes! Lightening is allover the grid not just in the locality! Its interesting that some filters seem to work others don't.
Fact: If the noise level is high in any equipment you will not hear a small change in the noise floor! Most people do an RFI clean up and say they can not here the difference so they put it all back as it was! Then they must have done something wrong because it doesn’t sound as good as it did before the mod!
Fact: RFI on mains will effect jitter on equipment it is difficult to filter due to the wide spectrum!
I am learning a lot from this thread e.g how the supply is structured in other countries, tests done by others! Thank you for your input.
It is a bit off topic sorry!
Regards
M. Gregg
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LMAO. If you connect the active and neutral wires around the oposite to what they were originally then there will be absolutely no difference to what you will hear or see.
If you however decide to twist the 2 wires together whilst at the same time stretching them, you will then get a sound that is twisted to the brain and will have extended lows.
Now that we've all had our fun, let's remember two important points that emerged from this discussion:
1. AC power as it comes from the outlet is not balanced or floating. One side is grounded. Therefore the AC voltages on the 2 AC legs, relative to ground, are very different from each other.
2. Many power transformers have different leakage to the core and ground depending on which primary lead you measure from.
So how is it again that changing the AC primary polarity can't possibly make a difference?
Granted, with good layout, star grounding, etc. the effect can be mitigated...
1. AC power as it comes from the outlet is not balanced or floating. One side is grounded. Therefore the AC voltages on the 2 AC legs, relative to ground, are very different from each other.
2. Many power transformers have different leakage to the core and ground depending on which primary lead you measure from.
So how is it again that changing the AC primary polarity can't possibly make a difference?
Granted, with good layout, star grounding, etc. the effect can be mitigated...
Michael and All,
Giving more thought to transformers and grounding most of the transformers we use are not isolated or floating. The secondary winding could float but be we do not allow that to happen. We pick one end or the other sometimes the center tap and tie it to ground, typically the same ground as the grounded neutral conductor that carries current to one end of the primary. Check any and every transformers wiring hookup directions sheet. You will find the polarity marked with a prominent black dots on the sheet for both primary and secondary connections especially important if there are dual primary and or secondary windings. Go to the Home Depot come home with a right hand bath tub and try to put it in a left hand hole. The only time it does not make a difference is if it is symmetrical like a claw foot tub. Sorry for the plumbing analogy.
Not to throw a wrench in and chip the porcelain it would be the same issue with polarity and symmetry with a 220 volt primary, where neither phase is grounded. Polarity still makes the difference. The black dots are still on the wiring diagram.
DT
All just for fun!
In theory it may change the level of hum in the system, although from a CD player I doubt it is measurable.
Many things I read about and that audiophiles hear are down to changes in perception of the user. Just standing up, powering down, plugging in the same plug the same way and returning to your seat will change you enough to hear a difference, sometimes quite a large one as your mood and perception shifts.
If you try a blind listening test with a friend switching polarity hidden from view and get 8/10 guesses correct than I'll believe you heard a difference - but only then
. And I bet you can't hear any difference in this case!PS I'd do the test with you but I live too far away from you - sorry!
Globulator,
You may be correct, however if we power equipment with a battery or with the mains "rectified etc" do we here a difference? We should hear no difference because its all just smooth DC isn’t it. However you will say not true because you will not have perfect DC from a power supply and the impedance will be different. Could we tell the difference if we blind test? Perhaps not if the equipment is very good. However one will still be better than the other from a test measurement point of view! Does RFI effect the ability of a cd player to track the CD correctly some people will say yes it does, can you hear a difference in a blind test?
I guess the matter is subjective in that any noise will effect the ability of the equipment to reproduce only what has been recorded but then again, is what has been recorded actually correct!
Some people say that if you blind test on very high end HIFI you cannot hear the difference between valve and FET amps.
You have got to admit it raises a lot of questions! If anything that can be measured but not be heard in a blind test is not important, why try to improve the equipment beyond the blind test? Some people will say that frequency response beyond hearing range is pointless, others will say the resultant harmonics from the beyond hearing range change the frequencies within hearing range when they are mixed!
Regards
M. Gregg
You may be correct, however if we power equipment with a battery or with the mains "rectified etc" do we here a difference? We should hear no difference because its all just smooth DC isn’t it. However you will say not true because you will not have perfect DC from a power supply and the impedance will be different. Could we tell the difference if we blind test? Perhaps not if the equipment is very good. However one will still be better than the other from a test measurement point of view! Does RFI effect the ability of a cd player to track the CD correctly some people will say yes it does, can you hear a difference in a blind test?
I guess the matter is subjective in that any noise will effect the ability of the equipment to reproduce only what has been recorded but then again, is what has been recorded actually correct!
Some people say that if you blind test on very high end HIFI you cannot hear the difference between valve and FET amps.
You have got to admit it raises a lot of questions! If anything that can be measured but not be heard in a blind test is not important, why try to improve the equipment beyond the blind test? Some people will say that frequency response beyond hearing range is pointless, others will say the resultant harmonics from the beyond hearing range change the frequencies within hearing range when they are mixed!
Regards
M. Gregg
The issue of mains phase reversal can only cause the electric field amplitude within the transformer to move, so (e.g) if the primary HT side moves from the inside of the bobbin to the outside you will pick it up better with any high impedance stuff next to it. This is why you may hear a change.
A battery has a different impedance like you say, and also zero hum (and a different noise signature). In a CD player however the actual power section has to get the transport and digital parts correct (easy) and also power the usually cheap opamps in the output (more difficult). The better PSU you can get powering the DAC the better, although having seen the waveforms on moderns CDs directly there seems little point going too far.
Improving equipment beyond what you can hear in a blind test is pointless. I mean - what would the point be?
Your harmonic argument is a different argument and if you can hear them a blind test will be just as valid
Improving equipment beyond what you can hear in a blind test is pointless. I mean - what would the point be?
Your harmonic argument is a different argument and if you can hear them a blind test will be just as valid
Improving equipment beyond what you can hear in a blind test is pointless. I mean - what would the point be?
Synergy
The sum of the mods combined create an improvement greater then the individual mods!
Your harmonic argument is a different argument and if you can hear them a blind test will be just as valid.
I stand corrected (Off topic)
Regards
M. Gregg
When I was young I reached to switch the small lamp on my nightstand. Non polarized plugs on the old lamps. I got shocked by touching the internal metal area that the bulb screws into or perhaps an exposed area of the bulb's threads. I could see the area. The socket's insulation was either too short or had cracked off somewhat. Not a horrible shock but enough to make me pay attention to polarity whenever I change a lamp cord. I’d much rather touch a neutral that a hot leg
Beyond 20K Hz. Can we hear it? Yes few of us directly most of us indirectly. It is not just some people say. It is the people in the lab coats call it beat frequency. Bats use it to pick bugs out of the air in the dark. We use it to create a dimential sound stage. Ckeck out Beat (acoustics) - Wikipedia, the free encyclopedia)
DT
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