[Freo-1]

Found an interesting link on one of the audio forums:
 
http://www.audiograph.se/Downloads/PowerCube_12p_brochure_complete.pdf
 
This helps explain why power ratings and test results can be deceiving.  This test should be run on all amps reviewed, but one does not see it very often.  It does help explain why a 30 watt or 60 watt Class A amp can provide cleaner power than say a 100 to 200 watt amp where the power supply reserve is simply not there.

[DS-21]

I wish Stereophile would pick up a Powercube, so that we could see more useful amp tests in the US.

But note actual Powercube tests that have been conducted (see the back issues of The Audio Critic for a bunch of 'em) don't show that "a 30 watt or 60 watt Class A amp can provide cleaner power than say a 100 to 200 watt amp where the power supply reserve is simply not there."

Chances are, a 100W or 200W amp is going to play louder cleaner longer than a 60W amp, regardless of class.

[Freo-1]

The power cube would tell us a lot more about a given amp than conducting just the “standard tests”.
 
If one looks at the power supplies of a beefy Class A amp, there is more than enough reserve to handle transients in such a manner that the resultant signal from them will often be more accurate/better sounding than some higher powered amp that does not have the power supply reserve on hand (especially when impendence drops).  I think most of us have experienced this somewhere along the way.

[cheap-Jack]

Hi.

Found an interesting link on one of the audio forums:
 
http://www.audiograph.se/Downloads/PowerCube_12p_brochure_complete.pdf
 

The PowerCube tests were carried out on a theoretical load of either pure resistance (0), pure capacitance (-) & pure inductance (+).

BUT, but realworld loudspeaker loads are a REACTIVE AC network, a vector summation of resistance, capacitance & inductance.

I'd be very interesting to see HOW PowerCube performs on the real thing.

c-J

[Speedskater]

In fact the PowerCube tests are never at pure capacitance or at pure inductance!

The tests are at:
Resistance
30º Capacitance
60º Capacitance
30º Inductance
30º Inductance

Never does it test at:
90º Capacitance = Pure Capacitance
90º Inductance  = Pure Inductance

[cheap-Jack]

Hi.

In fact the PowerCube tests are never at pure capacitance or at pure inductance!

The tests are at:
Resistance
30º Capacitance
60º Capacitance
30º Inductance
30º Inductance

Never does it test at:
90º Capacitance = Pure Capacitance
90º Inductance  = Pure Inductance

But NOT as shown in the block drawings, IMO. Otherwise, the block should have been drawn differently to reflect the curve of the combined REACTIVE effect.

c-J

[Speedskater]

The drawings look correct to me.

In the above referenced paper, skip the first few pages and look at the larger drawings near the end of the paper.

[DS-21]

The power cube would tell us a lot more about a given amp than conducting just the “standard tests”.

Agreed. I wish every published amp test had a Powercube.

However, let's forget "would" for a moment. "Would" is kind of pointless when there are actual data to study, wouldn't you agree?

What Powercube results have shown in the past is simply not what you claim they will show. Overbuilt underpowered amps do not as a rule perform better than more balanced AB designs.

If one looks at the power supplies of a beefy Class A amp, there is more than enough reserve to handle transients in such a manner that the resultant signal from them will often be more accurate/better sounding than some higher powered amp that does not have the power supply reserve on hand (especially when impendence drops).

Again, the actual measured data reveal your claims to be be ill-founded conjecture based on the audiophool's only truly active sensory organ: her/his eyes.

Stacking lots of impressive-looking parts in an amp, that means little to nothing. It looks impressive to the layman such as you or me, but says nothing about how the piece performs.

Before you spout off some more, why not look at some of the Powercube results in back issues of The Audio Critic? Data trump lay conjecture.

[medium jim]

Agreed. I wish every published amp test had a Powercube.

However, let's forget "would" for a moment. "Would" is kind of pointless when there are actual data to study, wouldn't you agree?

What Powercube results have shown in the past is simply not what you claim they will show. Overbuilt underpowered amps do not as a rule perform better than more balanced AB designs.

Again, the actual measured data reveal your claims to be be ill-founded conjecture based on the audiophool's only truly active sensory organ: her/his eyes.

Stacking lots of impressive-looking parts in an amp, that means little to nothing. It looks impressive to the layman such as you or me, but says nothing about how the piece performs.

Before you spout off some more, why not look at some of the Powercube results in back issues of The Audio Critic? Data trump lay conjecture.

Freo-1:

Haven't we been down this road before?  I will take my 70watt Tube Mono's which have a ultra beefy power supply over any wimpied power supplied 200watt amp any day of the week.  No conjecture, reading what someone else has said, just good old first hand experience.

[Freo-1]

Freo-1:

Haven't we been down this road before?  I will take my 70watt Tube Mono's which have a ultra beefy power supply over any wimpied power supplied 200watt amp any day of the week.  No conjecture, reading what someone else has said, just good old first hand experience.

 
We have been down this road before, and there is always someone with their own alternative reality.

For Example, look at the power supply (along with the reserve capacity) of a XA 60.5, and compare that to a mass market 150 or 200 watt amp, and the power cube (as well as other testing) will sort out the wheat from the chaff. (or truth from nonsense, as it were).
 

[Freo-1]

Agreed. I wish every published amp test had a Powercube.

However, let's forget "would" for a moment. "Would" is kind of pointless when there are actual data to study, wouldn't you agree?

What Powercube results have shown in the past is simply not what you claim they will show. Overbuilt underpowered amps do not as a rule perform better than more balanced AB designs.

Again, the actual measured data reveal your claims to be be ill-founded conjecture based on the audiophool's only truly active sensory organ: her/his eyes.

Stacking lots of impressive-looking parts in an amp, that means little to nothing. It looks impressive to the layman such as you or me, but says nothing about how the piece performs.

Before you spout off some more, why not look at some of the Powercube results in back issues of The Audio Critic? Data trump lay conjecture.

 
Kindly check your poor attitude at the door, mate. Please leave it out of here.
 
In fact, that is what is good about the power cube.   It gives one an idea of how an amp would perform in the real world as opposed to simple bench testing.
 
Look at these specs, and see for one's self:
 
XA60.5 / Specifications
Gain (db)26Power Output /ch (8 ohm)
60
Power Output /ch (4 ohm)
120
Input Impedance,(Kohms)
30 / 20
Leaves Class A @ pk Watts
120
 
These will go up towards 200 watts peak with no problems.  When it comes to high quality amps, it really IS about the power supply first.   

 

[DS-21]

Check your poor attitude at the door, mate.

Poor attitude is ill-informed speculation, when in fact there is data available from this device on real existing amps, free for the taking.

It may not conform to your ideology, but we all know about ideologies and evidence...

In fact, that is what is good about the power cube.   It gives one an idea of how an amp would perform in the real world as opposed to simple bench testing.

Nobody ever claimed otherwise, of course.
 

Look at these specs, and see for one's self:
 
XA60.5 / Specifications

That's not Powercube data, so how is it relevant to anything else written this thread?

[Freo-1]

Sticking to facts is what the Lab thread is about.
 
For example, this statement  made eariler is simply wrong:
 
" Chances are, a 100W or 200W amp is going to play louder cleaner longer than a 60W amp, regardless of class."
 
 The argument you present about Class A power supplies like the XA 60.5 is simply inaccurate.  The parts, (along with the engineering design), is what proves that out (as well as testing).
 
I would love to get a copy of a test with the Power Cube connected to the XA 60.5, as I am confident it would show that the amp has a lot of reserve power available. 
 
 
At any rate, let’s get back on topic:
 
The power cube shows why there can be such disagreements about amps in general.  If one’s speakers are a fairly easy load, then a pedestrian amp (or AVR) may work OK in that application.  However, many of the speakers audiophiles prefer can present challenges to that pedestrian amp.  This is where an amp with a well designed power supply (and output topology) comes into play.  It also explains why some amps with a lower power output at 8 ohms are actually “better” at driving those same preferred audiophile speakers.

[DS-21]

Sticking to facts is what the Lab thread is about.

I hope so!
 

For example, this statement  made eariler is simply wrong:
 
" Chances are, a 100W or 200W amp is going to play louder cleaner longer than a 60W amp, regardless of class."

That is an unsupported and conclusory assertion, not a fact.

Words mean things.

The argument you present about Class A power supplies like the XA 60.5 is simply inaccurate.  The parts, (along with the engineering design), is what proves that out (as well as testing).

Again, unsupported and conclusory assertion, not a fact.
 
Words mean things.

I would love to get a copy of a test with the Power Cube connected to the XA 60.5, as I am confident it would show that the amp has a lot of reserve power available.

You and your "woulds."

"Would" is a word used for idle speculation, not fact.

Why not look to the actual data available and see if your hypothesis is the least bit supported? 

You seemed to agree with me that sticking with facts is important. Why have you so utterly failed to find a single fact?
 
Peter Azcel is a man who knows a thing or two about the "sound" of amplifiers.

He has also published more Powercubes on home audio amplifiers than any other American source. All of his Powercube measurements are available for free on theaudiocritic.com. Both of the preceding statements in this paragraph are facts that cannot reasonably be disputed by anyone of good faith.

Why are you so afraid to go to that well of knowledge, after touting the measurement machine he uses?

(I'm willing to bet you had no idea that TAC did Powercubes. You were hoping to find some new device to cloak your religion in the mantle of science, without the inconvenience of actual data to mess with your weltanschauung. Though this parenthetical is, admittedly, not fact but merely my own speculation.)

The power cube shows why there can be such disagreements about amps in general.

If you're going to make such sweeping (and erroneous) assertions, please back them up with, you know, facts.

The only relevant facts, in this case, would be Powercubes for amps that have been shown in controlled listening to sound different when all other variables (audiophools' eyes, expectation bias, level, etc.) are eliminated from the equation and sound is all that remains.

However, many of the speakers audiophiles prefer can present challenges to that pedestrian amp.  This is where an amp with a well designed power supply (and output topology) comes into play.  It also explains why some amps with a lower power output at 8 ohms are actually “better” at driving those same preferred audiophile speakers.

The only thing that saves you here is the use of words of weasel such as "many." "Many" means the same thing as "some." Both mean nothing more (or less) than "more than one." Use of "many," rather than "some," is merely a semantic trick to signal that the narrator is on that particular side. Yes, there is certainly more than one poorly designed loudspeaker favored by "audiophiles." (I can probably name several dozen off the top of my head.) But going back to facts, you just haven't provided any. Just conclusions. To a thinking person, there is a difference between the two.

[Freo-1]

I hope so!
 
That is an unsupported and conclusory assertion, not a fact.

Words mean things.
 

And the word here is nonsense.

Here is a quote from Stereophile on the XA 30.5 test results:

" Pass Labs' XA30.5 is a Jekyll-and-Hyde amplifier. Ostensibly a 30Wpc class-A design, its measured performance reveals that it can actually deliver clipping-free peaks 6dB higher in power, while the fact that its distortion under those conditions is predominantly the subjectively innocuous third harmonic is commendable"

There are 100 watt amps out that don't perform as well.   The XA-60.5 is two XA 30.5 amps configured for mono. 

Here is a link to the review:

http://www.stereophile.com/solidpoweramps/pass_labs_xa305_power_amplifier

Recommend you stay off the Audio Critic dogma.  He has an agenda as much as anyone else, and maybe more so than most.  There are existing rules on this about A/B/X testing, so let stick to that.  Just because one reads something from the internet, it does not make it true.

The above are "facts", so stop whining.  This is not the circle to spread the "All amps sound the same" propaganda.  They work different, so guess what, they can and will sound different as result.  You don’t need a spectrum analyzer to tell that, either.

[*Scotty*]

DS-21 is this instance I will give Freo-1 a pass on his assertions in regards to the Passlabs XA60.5.
Here are links to the published specs of the XA 60.5
https://passlabs.com/products/amplifiers/xa.5/xa60.5
https://passlabs.com/images/uploads/manual/xa60_5-om.pdf
Link to a handy OHMS LAW Calculator
http://www.ohmslawcalculator.com/ohms_law_calculator.php
Link an explanation of Class A amplifier operation.
http://sound.westhost.com/class-a.htm
The Passlabs XA60.5 appears to be a variant of a push-pull Class A design, it idles at about 70% of the current necessary to supply 60watts into 8ohms RMS.
I do have doubts about the amplifier producing more than 128 watts per channel into 8ohms.
The peak voltage spec is given as 32 volts. If this voltage is applied to an 8ohm load, the maximum power available is 128 watts. This 3dB higher than the rated output.
 It is hard to determine what the amp will do into a 4 ohm load from the specs available. We can't tell how stiff the power supply actually is or how much the rail might sag when the amp sees lower impedance loads.
 If it will double its power on a dynamic basis into a 4 ohm load this would be equal to 256 watts and 32 volts out, it may be able to do this on a RMS basis.
The Powercube for the XA60.5 would look a lot like cube into resistive loads on this based on the above values.
Scotty

[Freo-1]

DS-21 is this instance I will give Freo-1 a pass on his assertions in regards to the Passlabs XA60.5.
Here are links to the published specs of the XA 60.5
https://passlabs.com/products/amplifiers/xa.5/xa60.5
https://passlabs.com/images/uploads/manual/xa60_5-om.pdf
Link to a handy OHMS LAW Calculator
http://www.ohmslawcalculator.com/ohms_law_calculator.php
Link an explanation of Class A amplifier operation.
http://sound.westhost.com/class-a.htm
The Passlabs XA60.5 appears to be a variant of a push-pull Class A design, it idles at about 70% of the current necessary to supply 60watts into 8ohms RMS.
I do have doubts about the amplifier producing more than 128 watts per channel into 8ohms.
The peak voltage spec is given as 32 volts. If this voltage is applied to an 8ohm load, the maximum power available is 128 watts. This 3dB higher than the rated output.
 It is hard to determine what the amp will do into a 4 ohm load from the specs available. We can't tell how stiff the power supply actually is or how much the rail might sag when the amp sees lower impedance loads.
 If it will double its power on a dynamic basis into a 4 ohm load this would be equal to 256 watts and 32 volts out, it may be able to do this on a RMS basis.
The Powercube for the XA60.5 would look a lot like cube into resistive loads on this based on the above values.
Scotty

Thanks.   The Pass Labs gear is top notch.
 

DS-21, the group of folks who subscribe to “The Audio Critic” school can be difficult to discuss audio with.  While I support the general concept of “sticking to facts”, the truth with audio is that some facts can be subjective as well as it can objective (Case in point: Class A amps sound subjectively better).  Audio is one of those subjects that are routinely referenced as “75% science and 25% art” (Or in this case: Subjective vs. Objective) Hint: It’s always the art that get argued about.

Just because someone does not agree with your view does not make them wrong, mate.  As much as I place emphasis on the engineering principals behind audio, there are some of sound reproduction that (existing) measurements cannot convey adequately.   Please stop  with the attitude.  Let's try to keep civil about this, shall we?

[Freo-1]

What I’m really curious about is how the latest Class D amps would measure with the power cube?  Has anyone seen measurements using a power cube with them? 

[*Scotty*]

If the power supply is adequate to the task I think it is possible that a UcD module or nCore based amp might fair well on this test given that the output filter is in the feedback loop.
Scotty

[kevinh]

What I’m really curious about is how the latest Class D amps would measure with the power cube?  Has anyone seen measurements using a power cube with them? 

Typically you can get an idea of how they will perform by looking at their relative performance into 8ohm/4ohn/2ohm to see where current limiting occurs, of course this doesn't test for stability into reactive loads. The power cube does give a good sense of how an amp will perform into real world loads.