Power cords, a trip into the unknown!

[Old Listener]

Mine [enthusiasm] is waning , seeing the industry simply becoming a Luxury one, things beceom more expensive by the day where in ALL other technological endeavore the contrary is the norm. While the cost to produce better products decreases the price of such gears, aside fro a few exceptions steadily rises too often to ludicrous level and frankly I am bothered by that

Frantz, I am in agreement with your assessment and your personal reaction to the state of high-end audio.

l am not accusing the whole audiophile community of rejecting science but if I were to just gleam around here in the WBF, the tendency to reject science is patent. Many (not all) do proclaim that some phenomenon can heard but cannot ever be measured so what to make of that?

WBF is a bit more bipolar than many audio forums. Usually, a forum coalesces around a set of shared beliefs and heretics are driven out. I'd guess that 50-60% of frequent posters are convinced subjectivists and 20% are convinced objectivists.

I joined WBF because of Sean Olive's posts. He's gone and most of the other experts are gone too. I read audio forums and other audio web sites to learn as much as to chat. Not much of interest here anymore.

There are lots of audio topics I'd like to hear about. Some solid information about what's happening in the audio industry (mid-fi and high-end) would be welcome. Some measurement based information on what you get in speakers at different price levels would be very useful. On the other hand, yet another vinyl vs. digital thread is just forum pollution to me.

Bill

 

[RBFC]

I joined WBF because of Sean Olive's posts. He's gone and most of the other experts are gone too.

Sean is not "gone". One extreme difficulty in getting a high degree of participation from our experts is a conflict of interest on their part. They get paid for doing the same thing we request from them for free. While they have graciously contributed some terrific information, it's unrealistic to expect them to be here regularly. I read on some combatives and tactical forums, and the same phenomenon occurs there. Respected experts stop by occasionally, so we really can't expect too much more. We have, however, given these experts a dedicated space here, something other forums typically do not.

I read audio forums and other audio web sites to learn as much as to chat. Not much of interest here anymore.

I'd ask that you consider that WBF is in its infancy. We hope that solid members such as yourself would help us to grow by contributing topics of interest. I've been active on internet forums for ~15 years. Our growth here has been steady, with quality material and high signal/noise ratio being a goal. Bill, this post is not directed solely at you. We've had this conversation with other struggling members too. We need folks who are "on the fence" to give it a shot to help us grow and become what the membership wants. One of the reasons WBF is "bipolar" is to allow subjective claims to be examined by objectivists in a cordial atmosphere. I believe that the truth is based in science, and many times subjective impressions are merely objective facts that have not yet been clearly enunciated in scientific terms.

One of the benefits of a "smaller" membership count is that the opinions and contributions of individual members, like yourself, mean much more and help to steer the forum forward. We truly value our members, and want to progress into an even better resource.

There are lots of audio topics I'd like to hear about. Some solid information about what's happening in the audio industry (mid-fi and high-end) would be welcome. Some measurement based information on what you get in speakers at different price levels would be very useful. On the other hand, yet another vinyl vs. digital thread is just forum pollution to me.

Bill

Bill, one of the big discussions occurring with the Admin team is exactly what you're stating here. I'd ask that you understand that being "perfect" at this early juncture is a huge task, but we are committed to improvement.

Lee

 

[microstrip]

(...)
One of the reasons WBF is "bipolar" is to allow subjective claims to be examined by objectivists in a cordial atmosphere. I believe that the truth is based in science, and many times subjective impressions are merely objective facts that have not yet been clearly enunciated in scientific terms.

One of the benefits of a "smaller" membership count is that the opinions and contributions of individual members, like yourself, mean much more and help to steer the forum forward. We truly value our members, and want to progress into an even better resource. (...)
Lee[/color]

Lee,
Good points. But what is an objectivist and what what is a subjectivist? As you outlined the interest of the forum in on the individual experiences and opinions. Perhaps the gap can me much smaller than expected if we meditate on this text of Floyd Toole, taken from his article "Audio – Science in the Service of Art"

Two-channel stereo, as we have known it, is not a “system” of recording and reproduction. The only “rule” is that there are two channels. At the recording end of the chain, there are many quite different theories and practices of miking and mixing the live performance – ranging from the purist simplicity of two coincident microphones to multi-microphone, multi-track, pan-potted and electronically-reverberated mono. They all can be great fun, some of them even very good, but they are all different.
At the reproduction end of things, loudspeakers have taken many forms: forward facing, bipolar (bidirectional in phase), dipolar (bidirectional out-of-phase), omnidirectional, and a variety of multi-directional variants. These, and various sum/difference and delay devices, have been employed in attempts to coax, from a spatially-deprived medium, a rewarding sense of space and envelopment. In the two-channel world, therefore, the artists could not anticipate how their performances would sound in homes. It was left to the end user to create something pleasant. Stereo, therefore, is not an encode/decode system, but a basis for individual experimentation.

 

[RBFC]

Great point! As we demonstrated in this thread:

http://www.whatsbestforum.com/showt...mportant-to-you&highlight=speaker+positioning

We found common ground between the "perceived" and the science of the matter. It was mathematically demonstrated that positioning increments of "X" resulted in quite audible differences due to the science behind it, not merely the perception of the listener. One of the hallmarks of the WBF philosophy is to examine, rather than criticize blindly, claims based on their merits.

As long as individual experimentation and preferences are part of the audio experience, we can never fully discount the subjective report.

Lee

 

[Gregadd]

If things were perfect, what would be the point? Application is part science, part art. Both are inexact. I concede that too often that is used as an excuse to ignore science. The last time I checked scientists are hard at work both developing scientific theory and its application.
If you find that when I do y, x happens it is no less valid because you can not explain why. I know you may still have to prove x happens and that y is the cause.

 

[fas42]

Audiophiles are sometimes obsessed with the dimming of the lights when a large power amp is first plugged in and turned on. This initial surge powers up the transformer and the capacitor bank, and then it just hums along with a constant current draw.

Gary, I'm sorry to say this, but you could be leading people astray with a statement like that. One thing a conventional power supply most certainly DOESN'T do is "hum with a constant current draw". It is the complete opposite of an electric heater or incandescent light bulb, which very smoothly follow the voltage waveform as far as the current draw is concerned. No, with a normal power supply almost nothing happens until the mains voltage reaches close to its highly distorted maximum swing, and then there is a short, sharp current spike injected into the power transformer. Both the mains voltage waveform AND the current spike into the equipment look very nasty on the oscilloscope, no wonder so many systems have problems ...

Frank

 

[Orb]

Orb, I haven't seen that - no matter how hard an amplifier is working in the audiophile context. Even the biggest loudspeakers are only drawing fractions of an amp. The time constant of a large capacitor bank slows down the requirement from the other side of the capacitor bank (at the IEC) to such that I couldn't see the difference on an oscilloscope. The larger amplifiers have an even larger capacitor bank, and hence even less chance of any voltage sag.

Audiophiles are sometimes obsessed with the dimming of the lights when a large power amp is first plugged in and turned on. This initial surge powers up the transformer and the capacitor bank, and then it just hums along with a constant current draw.

Hmm, you seen the measurements from JA for some amps where the sag happens way before expected limits.
Even those with good performance can suffer voltage sag under 400 watts, but would need to dig through his measurements to get a real feel on the behaviour.

Cheers
Orb

 

[Orb]

Orb

I wasn't meant to be a bashing. if it was construed or interpreted as such , i apologize. I do however think that at times we need to face the facts that observations need to be more carefully conducted to conclude with the confidence we tend to infuse in many a discussion about audiophile items.
I would also add that you , Orb, make sure to remain level and centered. You references are almost always educative and I commend you for the quality of your research and the enthusiasm you display when it comes to the seach for better reproduced music in our homes. Mine is waning , seeing the industry simply becoming a Luxury one, things beceom more expensive by the day where in ALL other technological endeavore the contrary is the norm. While the cost to produce better products decreases the price of such gears, aside fro a few exceptions steadily rises too often to ludicrous level and frankly I am bothered by that ... Opening any of these Power Cords will show to any person with the inclination to investigate that they are simply a beautiful sheath with common wires and an oversize terminals (Plug and IEC sides) .. Measurements from these PC shows close to nothing and frankly their purpose is to pass current at a single frequency , one of the simplest task that an interconnect will ever have to do ... It is also too consistent that with out the knowledge of these PCs in the chain observations are closer to pure chnace than anything this side of tossing a coin ..
l am not accusing the whole audiophile community of rejecting science but if I were to just gleam around here in the WBF, the tendency to reject science is patent. Many (not all) do proclaim that some phenomenon can heard but cannot ever be measured so what to make of that?
There was no intent to bash but there was an intent to wonder about the validity of our conclusions about PCs.

Thanks Frantz for taking the time to explain your perspective, I appreciate I polarised your view so apologies for that.

Cheers
Orb

 

[fas42]

Just to throw in a touch more, voltage sag in reality is a very minor issue, and certainly can't be modified by any sort of of power cord fiddling. All it means is that you won't be able to run your amp to quite the volume you were hoping for before clipping. If it really bothers you, buy an amp with a bigger capacitor storage, or add more of your own capacitors if you're into DIY. Sag is a relatively benign behaviour ...

No, what's much worse is that the DC voltages are badly glitching, may not be obvious by simply looking at the oscilloscope, but the bad behaviour is certainly there. If you model a power supply even only vaguely close to a real life circuit you can see that it's impossible for a power supply to behave like the text books claim when an amplifying circuit is drawing decent current from it. This is one of the keys reasons why true class A and SET amps automatically sound better ...

Frank

 

[Orb]

Just to throw in a touch more, voltage sag in reality is a very minor issue, and certainly can't be modified by any sort of of power cord fiddling. All it means is that you won't be able to run your amp to quite the volume you were hoping for before clipping. If it really bothers you, buy an amp with a bigger capacitor storage, or add more of your own capacitors if you're into DIY. Sag is a relatively benign behaviour ...

No, what's much worse is that the DC voltages are badly glitching, may not be obvious by simply looking at the oscilloscope, but the bad behaviour is certainly there. If you model a power supply even only vaguely close to a real life circuit you can see that it's impossible for a power supply to behave like the text books claim when an amplifying circuit is drawing decent current from it. This is one of the keys reasons why true class A and SET amps automatically sound better ...

Frank

I tend to agree it should be minor, but I disagree it is relatively benign behaviour.
Not all amps use very well regulated power supply, especially at the lower price ranges.
That said even though I raised this, it was more of an interesting discussion point rather than something I am going to lose sleep over.

If one accepts (and to clarify not all feel it does and that is understandable and I am impartial) power cables can make a difference in a stable situation, then one should consider the potential implications on power amps that are not as well regulated and suffering voltage drops.
One mistake I mentioned was limiting thinking to big watt amps (like Gary), but there are lower powered pure class A amps that draw a lot of current.

Cheers
Orb

 

[garylkoh]

Hmm, you seen the measurements from JA for some amps where the sag happens way before expected limits.
Even those with good performance can suffer voltage sag under 400 watts, but would need to dig through his measurements to get a real feel on the behaviour.

Cheers
Orb

Orb, sorry I wasn't clear. I'm talking about driving an amplifier hard in the audiophile context. Not driving 400W into a resistor (or even a simulated network). It really shows the quality of the power supply when you start pushing the limits - and that's when a voltage sag will usually happen. On some amps, it starts far sooner than in other amps.

With is enough capacitance, large bass dynamics can be buffered - even when the power cord is unplugged.

 

[Orb]

Ah k thanks Gary for clarification, makes sense.
Cheers
Orb

 

[garylkoh]

No, what's much worse is that the DC voltages are badly glitching, may not be obvious by simply looking at the oscilloscope, but the bad behaviour is certainly there.

I'm frankly puzzled - how do you know that the DC voltage is glitching if it cannot be seen (the glitch) on a 'scope?

 

[fas42]

I'm frankly puzzled - how do you know that the DC voltage is glitching if it cannot be seen (the glitch) on a 'scope?

Gary, as I said in a previous post, you treat the voltage supply as an audio input. Put a blocking capacitor on probes and link the leads to RCAs or XLR. Then "listen" to the sound of your power supply: the harder it's working the worse it gets ...

I love the unplugging the amp to check capacitor buffering thing: used to be a bit of a "party trick" of mine, but really was useful to get some feel of how much the mains input was directly affecting things. My previous amp setup was DIY gainclones with a pretty sophisticated power supply, quite a bit of capacitor storage. At normal listening levels I would get up to a couple of minutes of clean listening after pulling the plug ...

Frank

 

[DaveyF]

Today I am reading my new catalog from Music Direct...( plenty of good stuff in there). Anyway, I read about the new cables from Cardas...in the ad for the new Clear M power cord,I read this:

" Cardas' cutting edge power cord is the most complex design its ever created. The Clear M power cable provides broadband filtering on all three legs of the AC signal, making for visceral improvements in noise rejection and signal transfer. Incorporates a tuned toroidal filter and multipath cancelling conductors in a flexible, low resistance package".

Anyone know what the h...ll they are talking about

 

[fas42]

Anyone know what the h...ll they are talking about

The description would make some sense if I could see some bulk in the actual cable, looks very conventional to me. Any filtering components would be too tiny in value to have significant effect, from the the images I see of it. That's in my experience, that is ...

Frank

 

[j_n]

Measurements from these PC shows close to nothing and frankly their purpose is to pass current at a single frequency , one of the simplest task that an interconnect will ever have to do ..

No. That is unfortunately, too simplistic.
A power cord which is feeding a pure reactance is passing a single frequency. Typical supplies in the audio realm rely on a full wave bridge cap input supply. That design pulls a lot of higher harmonic current. So much so that it is many times important to consider derating the wire and breaker to accomodate those current peaks. In many cases, the 80% typical derate is insufficient, both for 60C wiring/breaker, and 75C.

In addition, NEC requires the neutral in a 3 phase system be considered a current carrying conductor when the three phase is driving non linear loads, typical of cap input hard supplies.

So the single frequency becomes fundamental in addition to lots of rather large odd order harmonics.

The second thing the line cord does, is safety bonding the chassis to the load panel. The intent is to clear the breaker in the even of a fault at the equipment..note that the purpose of the breaker is NOT to protect humans directly, nor the equipment. Only the wires from the panel to the outlet.

Unfortunately, one direct result of this chassis bonding is the completion of a ground loop. That is where one should look. Ground loop interference is not just hum.

.l am not accusing the whole audiophile community of rejecting science but if I were to just gleam around here in the WBF, the tendency to reject science is patent. Many (not all) do proclaim that some phenomenon can heard but cannot ever be measured so what to make of that?

Perhaps one need only look in the right place? Personally, I wouldn't even bother measuring a PC by itself. Other than ampacity (and perhaps magnetic symmetry), why bother?

There was no intent to bash but there was an intent to wonder about the validity of our conclusions about PCs.

Healthy questioning of pre-disposed conclusions is a good thing.

If I were so inclined to examine the possibility of a PC affecting my stereo, I would simply place a high bandwidth current probe over the poweramp line cord and push the system. Any net current at any frequency from DC to 50K that can be measured in this fashion shows that the system is poorly designed and may benefit from modification of it's interconnection scheme. (noet: if it is found that the music is modulating the ground loop current measured this way, re-positioning of any of the cables forming the loop may cause a change in the induced current amplitude and spectra.

Cheers, jn

 

[FrantzM]

No. That is unfortunately, too simplistic.
A power cord which is feeding a pure reactance is passing a single frequency. Typical supplies in the audio realm rely on a full wave bridge cap input supply. That design pulls a lot of higher harmonic current. So much so that it is many times important to consider derating the wire and breaker to accomodate those current peaks. In many cases, the 80% typical derate is insufficient, both for 60C wiring/breaker, and 75C.

In addition, NEC requires the neutral in a 3 phase system be considered a current carrying conductor when the three phase is driving non linear loads, typical of cap input hard supplies.

So the single frequency becomes fundamental in addition to lots of rather large odd order harmonics.

The second thing the line cord does, is safety bonding the chassis to the load panel. The intent is to clear the breaker in the even of a fault at the equipment..note that the purpose of the breaker is NOT to protect humans directly, nor the equipment. Only the wires from the panel to the outlet.

Unfortunately, one direct result of this chassis bonding is the completion of a ground loop. That is where one should look. Ground loop interference is not just hum.



Perhaps one need only look in the right place? Personally, I wouldn't even bother measuring a PC by itself. Other than ampacity (and perhaps magnetic symmetry), why bother?


Healthy questioning of pre-disposed conclusions is a good thing.

If I were so inclined to examine the possibility of a PC affecting my stereo, I would simply place a high bandwidth current probe over the poweramp line cord and push the system. Any net current at any frequency from DC to 50K that can be measured in this fashion shows that the system is poorly designed and may benefit from modification of it's interconnection scheme. (noet: if it is found that the music is modulating the ground loop current measured this way, re-positioning of any of the cables forming the loop may cause a change in the induced current amplitude and spectra.

Cheers, jn

HI

typical supplies in the audio realm rely on a full wave bridge cap input supply. That design pulls a lot of higher harmonic current. So much so that it is many times important to consider derating the wire and breaker to accomodate those current peaks. In many cases, the 80% typical derate is insufficient, both for 60C wiring/breaker, and 75C.

The designs doesn't "pull" harmonics, it generates. A full wave bridge rectifier doesn't use the harmonics in the 60 Hz wave, coming in, if it were the case we would be left with little power for the device itself ... Granted these harmonics can find their ways into the DUT (Love that acronym ). Now the derating concerns the power factor issue nothing to do with the Power Cord itself so if derating is needed, use larger wire gauge ...

In addition, NEC requires the neutral in a 3 phase system be considered a current carrying conductor when the three phase is driving non linear loads, typical of cap input hard supplies.

I am not sure I have ever seen a 3-phase Audio amplifier ....

Now in what way does a power cord changes the grounding scheme?

Now some questions: Has there ever been a study that shows the changes brought in an amp or other device by the substitution of Power Cords? ... If indeed there is such a study. has it been shown that the differences were repeatedly and reliably audible ?

 

[amirm]

Audiophiles are sometimes obsessed with the dimming of the lights when a large power amp is first plugged in and turned on. This initial surge powers up the transformer and the capacitor bank, and then it just hums along with a constant current draw.

I happen to have run a spice simulation of typical power amplifier supply, feeding two constant +-20amp loads (feeding the amp output stage). It nicely shows this effect:

The red is the current draw and shows a whopping +-270 amps of draw at start-up! Of course, this is in an ideal circuit and practical one may not have such high peaks but still, you can see the few milliseconds it takes it to get down to quiescent values.

The graph also shows the "haversine" shape of the current being pulled by the full wave rectifier that JN is talking about. If you are not familiar with what a haversine is, this is the formula:

 

[j_n]

HI
The designs doesn't "pull" harmonics, it generates. A full wave bridge rectifier doesn't use the harmonics in the 60 Hz wave, coming in, if it were the case we would be left with little power for the device itself .

Playing semantic games serves no useful purpose here, please refrain as it diverts from the discussion.

When a bridge is feeding a pair of caps, the currents that CAN BE MEASURED on the line cord trivially, is one loaded with 3rd, 5th, 7th, 9th order...etc, harmonics.

Stating that this circuit configuration does not cause harmonics on the line would be in direct contradiction to power engineering over the last 40 years or so. PFC front ends are finding their way further and further into the distribution chain, eventually most equipment will be pulling clean sines at a power factor of 1 by the time we run out of oil and gas for the power plants..

.. Granted these harmonics can find their ways into the DUT (Love that acronym ). Now the derating concerns the power factor issue nothing to do with the Power Cord itself so if derating is needed, use larger wire gauge ...

The derating is a direct result of the larger than normal peak currents in the harmonics. Cautionary tales about this effect has been in the power distribution industry well over 20 or 30 years. So much so that NEC gets into the act.

BTW, the derating applies to the breakers. As the conduction duty cycle lowers, the peak current rises, and the peak dissipation in the wire and breaker element goes up as the square.

.. I am not sure I have ever seen a 3-phase Audio amplifier ....

Whoa..interesting. I was giving a direct example from code. And, I actually have used one, it was about 15 kw, if I recall. Mil spec random vibe testing equipment..

.. Now in what way does a power cord changes the grounding scheme?

By it's grounding wire. The grounding wire's geometric relationship to the hot and neutral, the line cord's characteristic impedance (meaning the external magnetic field size), and the effective grounding resistance with respect to the overall grounding loop resistance.

.. Now some questions: Has there ever been a study that shows the changes brought in an amp or other device by the substitution of Power Cords?

Why would there? The first thing that happens when a power cord change modified a sound system is reported, the messenger is trashed as stupid, erratic, biased, a whole host of derogatory remarks, by many individuals who GLIBLY re-hash the gospel of "it's all in your head". The second thing that happens? Absolutely nothing is done to even consider the possibility that there is a clear and concise physics mechanism that describes the coupling mechanism (Ampere's law, Faraday's law, Lenz's law (for shields), so the question remains unanswered.

.. ... If indeed there is such a study. has it been shown that the differences were repeatedly and reliably audible ?

I have personally had the issue, figured out cause, effect, coupling, and solution.

Cheers, jn

Ah, ps...coupling between any amplifier current draw and a ground loop will be proportional to the frequency..as such, the higher harmonics are more likely to have an effect if there is system sensitivity to the problem. This also does not address musical content that finds it's way into the line cord either...measured already as well.

pps. sheesh amirm...you really don't like my monitor...