GR Research B24 AC Cord Review

[DualTriode]

A breadboard 12B4A amplifier.

Note: dBV scale on the graphic rather than some dBrA just floating there.

I put all the AC power cords and transformers in shielded boxes on the sort of damp concrete slab on grade garage floor. (concreate on grade is always sort of damp or your Ufer ground will not work)

Only DC and regulators on the bench. Different story with AC cords on the bench.

Note: only one AC peak in the noise floor, no power line harmonics

 

[spigot]

Some parts of this hobby aren't an endless series of subtle upgrades, which at some point just leaves the music as the next discovery. Thankfully.

 

[sonitus mirus]

Some parts of this hobby aren't an endless series of subtle upgrades, which at some point just leaves the music as the next discovery. Thankfully.

Then we could argue about whether free jazz is actually music or just a cacophony of noise.

 

[Somafunk]

 

[tomchr]

And that would be wrong.

You're assuming that all AV equipment is Class II (double insulated). It isn't all like that. Some is Class I (grounded chassis). That's what sets up trouble and that's also where a beefier power cord can potentially help.

Personally, I recommend Ott and Morrison when it comes to grounding. AES48-2005 is good too.

Tom

 

[amirm]

You're assuming that all AV equipment is Class II (double insulated). It isn't all like that. Some is Class I (grounded chassis). That's what sets up trouble and that's also where a beefier power cord can potentially help.

Not at all. Sit through a presentation by Bill and you see him re-iterate this that the same problem exists in both cases.

Personally, I recommend Ott and Morrison when it comes to grounding.

Henry (Ott) will tell you the same thing. Here he is from his book, Electromagnetic Compatibility which is bible of EMC:

Beyond this though, Bill's writings are far, far more to the point for people working with audio.

 

[amirm]

Note: dBV scale on the graphic rather than some dBrA just floating there.

And by doing that your reference is no longer at zero so you have to do gymnastics to interpret your results. All the peaks are now relative to -20 dB whereas mine was a much more convenient 0 dB. Any time I see someone post graphs like this, I know it is guaranteed that people will read the incorrectly, not realizing the reference not being zero.

There is a reason dBr (relative dB) was invented. It was for precisely this problem. You dismiss it and brag about it?

 

[tomchr]

All fine and dandy, but the parts you've highlighted have nothing to do with the error voltage I'm talking about. I'm talking about the voltage difference between the "ground" potential of two or more pieces of equipment plugged into the same circuit (or power strip).

It seems we need to split the problem into two parts:
1) Class I systems (grounded chassis, 3-wire power cord). Here I would predict that a heavier gauge power cord could make a measurable difference in the voltage difference between pieces of equipment plugged into the same outlet (or power strip).
2) Class II systems (floating chassis, two-wire power cord). Here I would expect power cords to have zero effect.

Tom

 

[amirm]

All fine and dandy, but the parts you've highlighted have nothing to do with the error voltage I'm talking about. I'm talking about the voltage difference between the "ground" potential of two or more pieces of equipment plugged into the same circuit (or power strip).

What? That is precisely what I am talking about. And what I quoted from Whitlock.

Regardless of what class equipment you have and what you do to equalize their ground connection, the internal leakages in equipment will change that. And with it, create ground loops. This is why messing with AC cords will do you absolutely no good in getting rid of ground loops.

So again, read the references provided.

 

[tomchr]

And again: Try to understand the problem.

What? That is precisely what I am talking about.

Is it? It's not what I'm talking about. What you quoted talks about ground potential differences between outlets in the same building. What I'm talking about is ground potential differences between pieces of equipment plugged into the same outlet or power strip.

Regardless of what class equipment you have and what you do to equalize their ground connection, the internal leakages in equipment will change that. And with it, create ground loops.

EXACTLY!!!!!!! And this ground loop will have an error current flowing in it. This can affect audio circuitry if the signal ground is referenced to chassis ground. If you decrease the impedance of the ground loop you will get a lower error voltage (unless Ohm's law is now fake news). One way to decrease the impedance of the ground loop is to use a heavier gauge power cord.

This is why messing with AC cords will do you absolutely no good in getting rid of ground loops.

Correct. You will not get rid of the ground loop. No power cord will do that. But you can lower the impact of the ground loop by choosing a beefier power cord.

Tom

 

[amirm]

And again: Try to understand the problem.

No, it is you that has such a rudimentary understanding of ground loops. I am shocked given your design experience but there we are.

EXACTLY!!!!!!! And this ground loop will have an error current flowing in it. This can affect audio circuitry if the signal ground is referenced to chassis ground. If you decrease the impedance of the ground loop you will get a lower error voltage (unless Ohm's law is now fake news). One way to decrease the impedance of the ground loop is to use a heavier gauge power cord.

No it isn't. You can mess with that all you want. If the voltage differential is created internally to the device, which is almost always the case, you are spitting in the wind. Once more, you need to read Bill's excellent papers and presentations. From the latter:

Anyone who has touched a double insulated device and gotten a "buzz" understands what he is talking about here.

The outlets themselves are also at different potential (ground) so it matters now how thick your AC cord is:

Here is the case of double insulated which would not even have an AC cord with a ground:

Clearly showing the problem with internal leakage due to stray capacitance.

Bottom line, changing the gauge of the AC cable is throwing a dart at the board, blindfolded and 100 feet away! It ain't going to do you any good except one in a million case.

 

[tomchr]

Sigh. Once again you're talking about devices without a ground connection. I'm talking about those with a ground connection.

I have already said that two-conductor power cords won't make a difference, so basically you're saying that you agree with me all while claiming that I don't understand ground loops. Further you now change the topic to be about equipment with two-conductor power cords when I was talking about equipment with grounded chassis - using three-conductor power cords similar to the one you reviewed.

What's next? Will you agree with me that the sky is blue all while claiming that I only have a rudimentary understanding of colours?

Tom

 

[amirm]

Sigh. Once again you're talking about devices without a ground connection. I'm talking about those with a ground connection.

Which I just covered:

How the heck the a few feet of AC cable has any impact on above?

And the first slide I post:

Right in your face it talks about 3-prong plugs.

A common theme here is that you refuse to read any references provided to you. Even when I quote it you don't read it.

 

[tomchr]

Yes. You're right. The slide mentions 3-prong cords in the context of safety limits. Congratulations. I'm not talking about safety, however. I'm talking about reducing the impedance of a ground loop. The first slide mentions the same voltage differences between outlets that you quoted from Ott that still aren't relevant because I'm talking about equipment plugged into the same outlet/power strip. I've said this multiple times now, so I really don't understand how you still think you have a valid argument.

An equally common theme is that you refuse to see perspectives other than your own. That's fine. Enjoy your echo chamber.

I have led the horse to water. He refused to drink. Too bad. So sad. Have a nice day.

Tom

 

[amirm]

Yes. You're right. The slide mentions 3-prong cords in the context of safety limits. Congratulations. I'm not talking about safety, however. I'm talking about reducing the impedance of a ground loop.

The safety limit shows you that a device can be UL compliant yet leak that much current. Once it does that, then there will be voltage drop over the unbalanced interconnect.

'm talking about reducing the impedance of a ground loop.

Which you can't do if the outlet ground has different voltage potential from another one.

I have led the horse to water. He refused to drink. Too bad. So sad. Have a nice day.

The day was fine. It was the evening that was ruined interacting with you defending complete nonsense about gauge of ground wire in an AC cable solving problems. Somehow you forget the tens if not hundred feet of wire behind the wall. That wire is 14 gauge and you think a 6 gauge AC wire of a few feet makes a difference in total impedance?

Now, it is not like you gave us many examples of how your solution works. Or measurements. You just throw out an argument hoping it sticks. Well, it didn't.

 

[Paco De Lucia]

I have worked 35 years in professional audio and have never heard of a single occasion where a mains cable caused problems/noise apart from, miss-wired, broken conductors, broken or worn connectors or conductors too thin (power amplifiers). Anything more than a safe properly specified mains cable is snake oil.

 

[Lambda]

t ain't going to do you any good except one in a million case.

1/1000000=0?
sure "one in a million case" is used synonymously of "Very rare" but very rare is not the same as never.

The safety limit shows you that a device can be UL compliant yet leak that much current. Once it does that, then there will be voltage drop over the unbalanced interconnect.

So the leakage current is something we have to life with because its perfectly save/normal
The voltage drop over the unbalanced interconnect is of cause depended interconnect impedance.

So a thicker and lower resistance RCA cable with lower impedance will pick up less hum from this perfectly save/normal leakage current?!

Strange how all your RCA cable tests show that cables make no difference...

Recoton RCA Cable Review (Ultra Cheap Cable)

This is a review and detailed measurements of the ultra cheap, "vintage," retail RCA cable. A member kindly sent it to me. It is not available anymore but I see two-packs on ebay for $4. The cable reminds me of the free ones you used to get in audio gear. It fits rather loosely on especially...

www.audiosciencereview.com

Why would you not simulate this unavoidable / normal leakage current in this test?

 

[restorer-john]

Or measurements. You just throw out an argument hoping it sticks. Well, it didn't.

Um, yes. It does stick Amir...

Do some basic differential ground/earth tests on various circuits/loops in your house and report back. Ground potentials vary massively- even on a simple circuit.

Just measured a ~2.0V ACRMS ground/earth delta on a 1200W (heater-PF 1.0) loop from one GPO to another. Maybe 10M max- one room to another.

Just like when you measure amplifiers- when did you last clarify and specify the line voltage? Hint: it make a big difference, especially with linear supplies.

 

[Paco De Lucia]

Um, yes. It does stick Amir...

Do some basic differential ground/earth tests on various circuits/loops in your house and report back. Ground potentials vary massively- even on a simple circuit.

Just measured a ~2.0V ACRMS ground/earth delta on a 1200W (heater-PF 1.0) loop from one GPO to another. Maybe 10M max- one room to another.

Just like when you measure amplifiers- when did you last clarify and specify the line voltage? Hint: it make a big difference, especially with linear supplies.

what does this have to do with the snake oil cable ?

 

[DonH56]

I skimmed a few pages and am completely lost... The safety ground, or lack of, has almost nothing to do with ground loops and leakage IME. Good and bad examples abound. The safety ground is usually tied to neutral and thence "earth" ground at the service box. Ground loops are all about the signal ground and how well it is isolated (or not) and routed among components.

As for the rest of the debate, it's not worth it to me to try to figure it out. Amir's measurements show the cord does reject some noise, but so would any shielded cable (heck, I splurged and spent $20 on a shielded extension cord recently "just in case" since it was routed near signal lines). All this is doing is burying the primary results and providing a heckuva' lot of fodder for others to laugh about.

Sadly, this is the trend with most reviews (not just here); the initial results are buried in pages of chaff so it's not really worth reading more than page 1.

IMO - Don