A good A/B test for a boutique power cable? (not a joke)

[alk509]

[quote author="Mbira"]I'm not sure if your read the original thread, but the alleged benefits acording to my teacher have been something along the lines of "Dude, it'll just melt your face at how huge the differences will be!!!!!!"[/quote]

I did read the original thread. What I meant was that unless you know what problem the 600-buck cable claims to fix, your tests will probably be inadequate and/or irrelevant. "It sounds better" or "it will melt your face off" aren't adequate test parameters - RF rejection and contact quality of the power cable and audio metrics taken of the same equipment using different power cables are.

Just listening to the thing is cool, but human hearing being what it is, your results will be attacked by half the people: either the "your ears are shot" audiophile crowd, or the "placebo effect" scientific crowd.

I was involved in the design of a double-blind, placebo-controlled informal "study" of audio improvements of this type (although not specifically power cables) and the results were interesting. I'll talk about it once this whole thing is done - don't want to influence your test results!

Peace,
Al.

 

[bcarso]

The problem I have with some high-endish listening is that I can't hear differences even when I know what is being presented and even when I want, earnestly, to hear the differences. This happened with a system into which a version of the infamous Tice Clock was introduced. Now admittedly the system was one I was not that familiar with and which I found somewhat "forward" (some modified JBL K2's fed from Quicksilver amps for the horns and a big old Mark Levinson for the woofers). Also the only software were CD's of female vocalists---a whole wall of CD's of that description with nary an orchestral recording (some readers may be able to guess whose system this was).

And yet I believe my hearing abilities are rather acute---I have nearly perfect pitch, and normal high frequency extension for a 57-year-old who has taken decent care of his ears (only in the last several years have I been unaware of the television flyback emissions). I'm also pretty good at identifying frequency response anomalies after a fairly short listening session.

When I had a first CD player and early software I was initially impressed, but found fatigue setting in after a few listening sessions, and setting in earlier each time. It became clear to me that a learning process was underway. I was accused by housemates of being prejudiced against digital audio by what I had read beforehand---but the fatigue was unexpected and quite real, as well as my initial enthusiasm. One other person insisted that I needed a more powerful amplifier, despite my ability to show that the existing one was not near clipping.

As both recordings and CD players got better I got to where I could listen happily for long periods, but this took years of evolution.

These experiences have led me to be somewhat suspicious of short-term A/B testing for everything. But certainly when people gas on about dramatic and immediately perceivable differences, these should certainly be evident in double-blind tests.

 

[Emperor-TK]

Back to seriousness for me (sorry for taking the thread towards comedy). Hopefully Dave and I will run similar tests in the near future so I am all ears , so to speak. Listening fatigue is a good point, but I think that it should be ruled out for this study, since the original claim was for an immediately obvious difference. Besides, that is also how most of these cables are described by proponents and company marketing. Imagine if they tried to sell a cable claiming that "you won't notice a difference at first, but in the long run you might be able to listen a little longer". That won't appeal to most buyers (but it might to me). I often wonder about marketing strategies. I'd personally be more open to trying a Mackie Onyx if the claim was "a great bang for the buck, high quality spillover pres" rather than a competetor to the best high end stuff.

I think the proposed A/B tests are valid here.

 

[alk509]

I propose a "how many plug-ins?" test, just to debunk your teacher:

1. Turn computer on using cheap power cord.
2. Open PT session with X number of tracks, all with a set number of plugins (say, three) and all muted; start unmuting tracks until computer craps out.
3. Close session, restart computer and repeat a few times to get an average of how many plugins can the computer run in the session.
4. Repeat steps 1 through 3 with $600 cable.
5. Compare results.

You're a brave man, Joel! :green:

Peace,
Al.

 

[chrissugar]

In my opinion it is obvious that his claim that a computer with the 600$ cable (or any other cable) will run more plugins is completely stupid.
Also, I think the chance to hear a difference on an average audio system without the power conditioner wil be probably zero.


Brad

I'm not talking about those audiofoolish things like that Tice Clock, cable direction and C37 laquer.
I'm talking about things that are reasonable and explainable with the laws of physics, mechanics and chemistry. We all know that "burning-in" is a normal process related to the chemical process of formating inside capacitors. Also a beefier PSU with good design and quality components will produce a cleaner DC for the electronics and that can influence how it will sound, proper shielding will protect better the electronics and it will perform better. In my opinion the well designed power chord (not the 600$ but the 55$ home made one), and a quality power conditioner are in the same direction like the other improvements. In my opinion it can be explained with the laws of physics, I don't see any sign of "snake oil".


I just think about the fact that for example the output level of a CD player in most of the cases is aprox 1Volt. A 16 bit converter has 65532 steps and if you divide the 1 volt with 65532 steps, one step is aproximately 15microvolt. All the noise that enter into a sytem that is not protected enough can be of a level where all the fine details can be lost in the noise. I think there is a logic in this. Or am I wrong?

chrissugar

 

[alk509]

[quote author="chrissugar"]In my opinion it is obvious that his claim that a computer with the 600$ cable (or any other cable) will run more plugins is completely stupid.[/quote]

Like I said:

[quote author="alk509"]just to debunk your teacher[/quote]

Peace,
Al.

 

[Mbira]

So if I am in fact able to get my teacher to formally retract his "face-melting" comment, and I do get the go ahead to do experements, I would like to mainly do
1) Test the amount of RF filtering straight off the end of the power cable going into a common powersupply. Maybe use a drill in the same outlet to increase RF and measure differences.
2) set up a room mic and just play three or four reference clips from CD's that I know well, record the two cables, post the results here and see if anyone can tell the differences.

That should take away most subjectivity.

Joel

 

[DrFrankencopter]

I think that any audible differences that you hear when going from a generic power cable to a fancy power cable reveal more about the design shortcomings of the thing you plugged it into rather than the design excellence of the cable itself.

Good gear *should* be designed to have adequate power supply noise rejection built in, and good power supplies have adequate filtering to prevent themselves from being obnoxiously noisy in the first place.

I honestly think that layout concerns and lead dress around the power supply inside the box will make orders of magnitude more difference than the design of the cable supplying the AC. I do have monitors that are accurate enough to reveal subtle differences (ATC SCM50As), but I'm not sufficiently convinced to bother making a cable and seeing for myself. There are many other things that I'd rather do first....like build more acoustic enhancers (bass traps/diffusers, etc).

Cheers,

Kris

 

[chrissugar]

[quote author="DrFrankencopter"]I think that any audible differences that you hear when going from a generic power cable to a fancy power cable reveal more about the design shortcomings of the thing you plugged it into rather than the design excellence of the cable itself.
[/quote]

Did you ever open a power conditioner made for audio equipment? I'm not talking about toys like APC of Furman but some serious equipment.
I did it two weeks ago.
It was a 40 kilogram, 4U rack with power connectors at the back panel.
Inside there were four 1000W isolation transformers, lots of ferrites at the hot, neutral and ground of every power connector and input cable, large filters with big inductors with thick wire and lots of capacitors, one filter like this for every power connector.
Also I understand that these isolation transformers have some kind of screen between the primary and secondary, conected to the ground to kill any kind of residual RF.
My question is do anyone think that this kind of extreme isolation and filtering can be included in any high quality audio device?
I don't think so. Just look to the equipment we use to make our tests and they are considered some of the best ones in the world.
If you look at the pictures in the PDF for this Boulder preamp/DAC it will be clear that it is top quality engineering:
http://www.boulderamp.com/pdf/1012DataSheet.pdf
I think most of the devices available are of lower quality and engineering.
Also the amp, is top of the line, linear from DC to 5MHz:
http://www.spectralaudio.com/dma-250.htm
I can't imagine better engineering than the one in these two devices.

[quote author="DrFrankencopter"]Good gear *should* be designed to have adequate power supply noise rejection built in, and good power supplies have adequate filtering to prevent themselves from being obnoxiously noisy in the first place.
[/quote]
Yes, you are right, but do anyone think that you can include in a box like the ones I'm talking about the powerfull filtering and isolation that is inside the 40 kilogram power conditioner?
I think an eficient isolation/filtering is not doable inside every audio device. It would take to much space, would be heavy and cost too much.
That is why I think inside every device is just a reasonable filtering and not an extreme (adequate) one.

Just think about the similarity between the CMRR of an input receiver built with opamps and transformers. You can't build a receiver based on opamps with similar rejection like a transformer. Does that mean that a receiver built with opamps is not designed to have adequate rejection. No. It is not the engineering but the limitation of what you can do with opamp in this case.


The problem is that we detected significant (not big but significant) improvement with the above devices when quality cable and power conditioner is used.


Brad

Please, can you ask your friend, Mr Keith Johnson (the designer of the above Spectral power amp) what he thinks about the use of power conditioning and quality power cables.

chrissugar

 

[bcarso]

I don't know how to reach Keith at the moment Chris, but if I do talk to him I will ask him about this.

I do know that he adopted the balanced a.c. power approach for the Pacific Microsonics workstations (see my post about the catastrophe when he got a piece of equipment that had a fault condition of a.c. neutral shorted to line level input common).

These balanced power transformers do act to some extent as line filters themselves, although I don't know how elaborately they are shielded.

One of the problems with transformers is that maximizing the coupling coefficient and minimizing the coupling capacitance are two conflicting constraints.

Cheap a.c. wallwarts and other multiple isolated bobbin trafos are pretty low in coupling capacitance---maybe 30-40pF typically---but also not very efficient (notice how warm they run under load). Of course the cores and wire are usually about the cheapest they can get away with as well, thus a small and easily saturated primary inductance, so without a load there are some significant losses too.

This has driven the requirement for high efficiency little switchers to replace them---but to get adequate performance the interwinding capacitance has gone up enormously (I've measured over a nanofarad), which creates more noise problems just from the greater coupling to the mains. I had a case of where a relatively unshielded consumer product was fine sitting on a table, with sensitive high-Z parts of the circuit seeing the predominately zero voltage of the environment when powered from a standard wallwart, but had a clearly audible buzz when used with a little switcher. This drove a modification that required some fairly extensive shielding.

When you stick shields in between windings they and their leadout wires have significant inductance, so the shield's effectiveness at high frequencies will be limited. Also look at where you are running that intercepted high frequency energy, and what you are going to do with it when you get there.

Fortunately, sufficiently high freq energy can be blocked (reflected) and also to some extent dissipated when absorbed by inductors and common-mode chokes.

How much of this needs to be inside of each piece of equipment is an interesting set of design tradeoffs. Properly executed pro equipment has a huge advantage in terms of the balanced interconnection scheme. But, you can still have plenty of high frequency energy spraying around and doing mischief, particularly with the amount of equipment using switching power supplies and ever-faster digital processors.

 

[Guest]

[quote author="chrissugar"][quote author="DrFrankencopter"]I think that any audible differences that you hear when going from a generic power cable to a fancy power cable reveal more about the design shortcomings of the thing you plugged it into rather than the design excellence of the cable itself.
[/quote]

Did you ever open a power conditioner made for audio equipment? I'm not talking about toys like APC of Furman but some serious equipment.
I did it two weeks ago.
It was a 40 kilogram, 4U rack with power connectors at the back panel.
Inside there were four 1000W isolation transformers, lots of ferrites at the hot, neutral and ground of every power connector and input cable, large filters with big inductors with thick wire and lots of capacitors, one filter like this for every power connector.
Also I understand that these isolation transformers have some kind of screen between the primary and secondary, conected to the ground to kill any kind of residual RF.
My question is do anyone think that this kind of extreme isolation and filtering can be included in any high quality audio device?
I don't think so. Just look to the equipment we use to make our tests and they are considered some of the best ones in the world.
If you look at the pictures in the PDF for this Boulder preamp/DAC it will be clear that it is top quality engineering:
http://www.boulderamp.com/pdf/1012DataSheet.pdf
I think most of the devices available are of lower quality and engineering.
Also the amp, is top of the line, linear from DC to 5MHz:
http://www.spectralaudio.com/dma-250.htm
I can't imagine better engineering than the one in these two devices.

[quote author="DrFrankencopter"]Good gear *should* be designed to have adequate power supply noise rejection built in, and good power supplies have adequate filtering to prevent themselves from being obnoxiously noisy in the first place.
[/quote]
Yes, you are right, but do anyone think that you can include in a box like the ones I'm talking about the powerfull filtering and isolation that is inside the 40 kilogram power conditioner?
I think an eficient isolation/filtering is not doable inside every audio device. It would take to much space, would be heavy and cost too much.
That is why I think inside every device is just a reasonable filtering and not an extreme (adequate) one.

Just think about the similarity between the CMRR of an input receiver built with opamps and transformers. You can't build a receiver based on opamps with similar rejection like a transformer. Does that mean that a receiver built with opamps is not designed to have adequate rejection. No. It is not the engineering but the limitation of what you can do with opamp in this case.


The problem is that we detected significant (not big but significant) improvement with the above devices when quality cable and power conditioner is used.


Brad

Please, can you ask your friend, Mr Keith Johnson (the designer of the above Spectral power amp) what he thinks about the use of power conditioning and quality power cables.

chrissugar[/quote]

i really like the black pc board...i wonder where i can find that (as shown in the first link)