[andy_c]

Occam,

No problem at all.  It took me a while to get back to you on this because I've been finishing my taxes and my internet connection keeps going down.

I would think balanced AC would tend to minimize the AC voltage induced in the chassis of isolated equipmant due to the capacitive transformer coupling.
I'd like to look at that schematic again now just to verify that, but I can't reach the site.  I think the DNS of my ISP is hosed   .

[MGDeWulf]

Being from Illinois, I've always observed green to mean ground.

Marty

[Steve]

You guys are right. Growing up in the 50s in a small town, I always heard green was neutral and white was common or ground.

Luckily, my wiring was always correct despite calling the wires by the wrong name.

Well, we will see if an old dog can learn new tricks.

Thanks for info.

[andyr]

Wow I've certainly learnt a lot reading this thread.  Mostly how people can be so stupid around the world!

First, can I suggest people (who are in "who knows" part of the world) specify their mains supply when they start to talk about mains.  Then readers know whether they are in a part of the world which allows you to easily "flip" your mains polarity by rotating your mains plug 180 deg (like the US) of does not (UK, Oz, NZ etc.) because it uses 3-pin plugs.

Secondly, how can people's logic be so different in different parts of the world.  After all, we're all homo sapiens!  

The mains supply has an active, a neutral and, in most places, an earth.  Active is the wire that will kill you so it makes sense ... to use red for this.  Then, some decades ago in Australia, anyway, some dickhead public servant said, because red colour blindness is a common affliction, the active line should be brown instead.  They also changed the neutral to blue - ie. instead of red/black we now had brown/blue.  

I would have thought that perhaps colour blindness should be a contra-indication of a career as an electrician - in just the same way that, if you're blind, you don't contemplate a career as an airline pilot - however, stopping someone from being an electrician is discrimination of the basest kind, so of course will not be tolerated.  And as we can't have electricians wiring up incorrectly - because this might kill innocent citizens - we MUST change the colours!  

Anyway, after the previous colour choices, to me green makes sense for the colour of the earth wire ... earth... grass... green etc.!!  By all means use white as the neutral - instead of the original black and subsequent blue - but to select green as the neutral, to me is bizarre.  

Now, while I'm on a good rant, I may as well get onto this topic of mains orientation.  Marty DeWulf's article clearly explains how to go about the task of testing what your voltage difference is between the chassis and the wall-socket earth.  It explains how you then reverse this (more difficult in 3-pin countries than the US ... you have to make up a short "extension cord" which has the active and neutral reversed, just for this test) to see which way round has the lowest reading.

And remember, when you do these tests, you have to make sure that temporarily, the earth pin on your power cord is NOT connected to the earth in the wall socket (if you have one).  The easiest way to do this in Oz in to interpose a "double adapter" between your component power lead and the wall socket ... having disassembled the double adapter and removed the earth contacts!

So I am amazed at the questions and comments which have arisen, which plainly show the posters were not able to understand Marty's article.  

What you are interested in here is the orientation of the power transformer primary winding vis-a-vis the mains active and neutral wires.  If the lowest voltage connection was obtained when you had the wiores reversed, you need to swap the transformer primary windings around - you DON'T reverse the active and neutral wires on the IEC socket as this will take the fuse out of the active side ... not a good idea!!  

Now, on the surface (and particularly to the sort of EE types who said 20 years ago that "a bit is a bit is a bit" ... so all CD players must sound the same!), the whole idea of "correct" AC mains orientation giving better sound seems garbage.  However, it's to do with the way the power transformer is wound.  If you're sceptical, just try it out ... then, when you become a believer, make sure all your mains switches are DPDT, like Occam, so you can readily flip the AC and listen to the difference!

Regards,

Andy

[Andrew B.]

This is an email reply I received from the engineering department at Benchmark Media when I directed them to the topic of this thread:

Subject: RE: DAC1 - reversing polarity of live/neutral power connection

 

The connection between the DAC1 transformer and the AC line is balanced.  There should be no benefit to this exercise.  There should also be no harm because the DAC1 has dual fuses (one on the hot, and one on the neutral.  But, be very careful because most devices do not have dual fuses, and you can create a fire hazard if you reverse the AC connections to such a device!

[Occam]

Andrew,

Thank you for that wonderful example showing that a, no doubt extremely competent, engineer can make such a pisspoor scientist.

There should be no benefit to this exercise.

To their credit, the word used was 'should' as opposed to 'is'.

Lemme get this straight -
1. there is a defined measurable metric, chassis potential that changes with 'plug orientation' (this of course, when both lines aren't switched/fused, the reversal is actually after the fuse/switch), when the ground is temporarily left unconnected. This is simply an objective measure, resulting from coupling from the power transformer and its actual physical construction.

2. When reconnected to ground, that chassis potential will flow to the ground line, signal grounds, and to other components.

3. there is a reported high correllation between  plug orientation/chassis potential and subjective evaluation.

4. a thought experiment concludes that there should be no benefit.....

If, like Dougless Self, Benchmark doesn't actually listen to their product and use subjective asscessment in their design process, but relies totally on measurements, I understand their logic. Otherwise, I can only hope that your respondent was a Marketing Engineer, rather that an actual Design Engineer.

What? It would take them all of a half hour to check it out? Maybe they are right, but they don't know this empirically.

[audioengr]

I suspect that most of the hum problems with Benchmark DAC-1 are mostly due to the fact that the input pulse transformer primary is grounded. This eliminates the real benefit of a transformer, and that is galvanic isolation.  I fix this as an option in my mod for the Benchmark, as well as replacing it with a better transformer.

[andyr]

Andrew,

Thank you for that wonderful example showing that a, no doubt extremely competent, engineer can make such a pisspoor scientist.

To their credit, the word used was 'should' as opposed to 'is'.

Lemme get this straight -
1. there is a defined measurable metric, chassis potential that changes with 'plug orientation' (this of course, when both lines aren't switched/fused, the reversal is actually after the fuse/switch), when the ground is temporarily left unconnected. This is simply an objectiv ...

Paul,

To his credit, the Benchmark engineer also pointed out that "you can create a fire hazard if you reverse the AC connections".

Indeed you can - all you want to do is reverse the transformer consections (if you've measured that "reverse power" is the lowest chassis voltage reading) ... unless you've implemented a DPDT mains switch like you and me have!  

Regards,

Andy

[Andrew B.]

Paul, the response was from John Siau who is a real electronics engineer. I did come across some very detailed postings he made on a DIY audio forum but unfortunately I have lost the link. All I have is a quote which is perhaps only tangentially relelvant but I will post it here since it demonstrates that he is a real engineer and that they have thought quite hard about the design of the DAC1:

"The audio path is well isolated from the power supply rails, and the power supply rails are bypassed to their own ground system (not to the audio ground reference). The DAC1 will run just fine with lots of ripple and noise on the power supply rails. The regulators (as generic as they are) are orders of magnitude better than they need to be. The DAC1 can actually run with several volts of ripple on the +/- 18 volt rails (we have run this test in the lab) without any measureable change in performance. The +5V and 3.3V regulators are the most critical. Excessive noise on the 5 and 3.3 volt rails can cause jitter. The filter caps on these rails are oversized, and there is no measurable jitter due to noise on these rails. Again, by injecting noise onto these rails, we know what the margins are, and we know that we will not gain anything by changing the regulators.

This is also why the DAC1 will not benifit from high tech AC line cords and/or AC line filters.

Here is one way to domonstrate this: The DAC1 is designed to operate with AC line voltages as low as 90 VAC. Below 90 VAC the +/- 18 volt regulators will drop out, and AC ripple will increase rapidly as the input voltage is decreased further. At about 80 VAC the DAC1 will gracefully shut itself down by applying each of three digital mute circuits. Just above 80 VAC the DAC1 will opearate normally with no detectable hum or distortion in spite of the fact that it is operating with the +/- 18 V regulators in a drop-out condition. At 80 VAC there is about 3 Vpp AC ripple on the +/- 18 V rails. The only negative impact on performance is that the ripple reduces the headroom of the analog outputs. Normally the DAC1 can deliver +29 dBu to the XLR outputs. When the power supply is out of regulation, the maximum output level is reduced to about +27 dBu."
John Siau
Director of Engineering

The metric as quoted by MGDW is a 1% voltage variance in the case of the Benchmark DAC chassis versus a 90%+ variance in the case of the Plinius amp. That 1% could be a measurement error, a temporary phenomenon and/or insignificant. Have you measured an effect with the DAC1? I also don't understand why you are imposing conditions on your statement 1 ("when both lines aren't switched/fused") which are in fact incorrect in the case of the DAC1, as the engineer explained.

Audioengr, are you saying there are ground loop issues with the DAC1 specifically? Or is "hum problems" a description of something else entirely? I haven't noticed any ground loop issues with my system using a coaxial connection. And with the optical connection they wouldn't be possible, would they?

Andyr, I thought what was being suggested by MGDW and others IS reversing the AC connections at the wall plug...

All very confusing still, I'm afraid.

Andrew

[andyr]

Paul, the response was from John Siau who is a real electronics engineer.  ...

Hi Andrew,

Nonononono    

Follow the logic through the chain ... if you only have a DPST (or even worse, a SPST) mains switch and, in doing MGDW's testing process you find that the "reversed" mains connection gives you the lower chassis voltage difference then, yes, you can certainly reverse the AC connections at the wall plug.

However, this is contravening your electrical code, as the fuse is no longer on the active side!

Reversing the connection at the wall plug (or on the IEC socket inside the case) has the effect of reversing the polarity of the mains on the power transformer primary - ie. what previously was the "active" side is now the "neutral" and VV.

You achieve exactly the same thing WITHOUT contravening your electrical code by simply flipping the connections of the power transformer primary at the power switch, inside the case.  Here, the fuse remains on the "active" side of the AC mains.

Regards,

Andy

[audioengr]

Audioengr, are you saying there are ground loop issues with the DAC1 specifically? Or is "hum problems" a description of something else entirely? I haven't noticed any ground loop issues with my system using a coaxial connection. And with the optical connection they wouldn't be possible, would they?

Yes, there are potential ground loops.  Lots of DAC designs make this error.  I usually fix it.  I can hear a little hum in my system with a stock Benchmark.

[Steve]

That is exactly right, Andy, and that is exactly how I do it. Switching After the fuse keeps the integrity of the hot wire fused while switching the primary of the transformer.


 black =hot, white =neutral, green =ground.

[Occam]

Steve,

You say tomato and I say tomato.
You say potato, and I say potato.



Grounded, Grounding
Grounded, Grounding
Lets call the whole thing off,
Lets call the whole thing off......

[Occam]

Andrew - What you are missing (or more likely, I'm failing to convey clearly) is that I dispute some of the assumptions implicit in John Siau's statements. (Quotes are from Mr Siau, bold is by me)

The DAC1 can actually run with several volts of ripple on the +/- 18 volt rails (we have run this test in the lab) without any measureable change in performance  ...... Again, by injecting noise onto these rails, we know what the margins are, and we know that we will not gain anything by changing the regulators.

I've no doubt that the DAC1 exhibits absolutely fabulous PSRR figures. Nor do I doubt that it is simply chockablock full current mirrors and sources that vastly improve whatever measurements they take with their instruments. But what is implicit is that subjective preference is not something worthy of measure. Which is fine by me.
I'm not a recording engineer. To be honest, a major part of any audio purchase is how that equipment pulls my monkey bone. And this is quite subjective. Now I'm not going all micropower SET upside your head, these components exhibit distortion characteristics that are below anything that has be shown discernable by human hearing. Now some of these components, developed by my betters, would improve both PSRR and distortion measures with the odd current source and/or mirror to improve the topology. I just don't like it as much. Go figure.

This is also why the DAC1 will not benifit from high tech AC line cords and/or AC line filters.

Pefect sound forever?
I've never heard a mains powered component the wasn't improved by a balancing conditioner.

I don't own a Benchmark nor do I have any experience with them. Nor have I ever encountered a solid state component with more than 20 volts on the chassis unless it had multiple tranformers and they were wired so that swiching leads stll left the coupled voltage additive. My comments were directed at the 'thought experiment' , Mr Saiu's " "Thus I refute you" rather than " I tried it, listened to it, and me and my buds couldn't tell the diff...." Maybe he is right. But IMO, that question is best answered empirically.

I'm pleased for anybody who can choose (let alone develop) a satifying system by specifications alone. Really.

[audioengr]

The DAC1 can actually run with several volts of ripple on the +/- 18 volt rails (we have run this test in the lab) without any measureable change in performance ...... Again, by injecting noise onto these rails, we know what the margins are, and we know that we will not gain anything by changing the regulators.

Well, I change the regulators and it makes a HUGE difference in the sound quality.  Tests in the lab??? Someone needs to do some LISTENING TESTS.  What a novel idea....

[Uptown Audio]

Chassis to earth ground. You should be getting millivolts difference, ie .005v Vs .012v, etc. you are not measuring mains voltage, just the best grounding scheme, so you are correct, in theory it should be zero.
-Bill