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Old 10th January 2012, 11:02 PM   #741
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Quote:
Originally Posted by Pano View Post
Step up transformers?
Yes. They were on a table when I experimented.
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Old 10th January 2012, 11:10 PM   #742
Pano is offline Pano  United States
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What do you see as the advantage of using the transformers as opposed to, E.G, differential mode on an o'scope? Anything other than the step up?
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Old 10th January 2012, 11:18 PM   #743
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Quote:
Originally Posted by Pano View Post
What do you see as the advantage of using the transformers as opposed to, E.G, differential mode on an o'scope? Anything other than the step up?
I used transformer because I needed to sense current through speaker driven by a pair of bridged amps. Otherwise one resistor to the ground would be simpler and better.
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Old 10th January 2012, 11:20 PM   #744
Pano is offline Pano  United States
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Bridged amps, right. Thanks!
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Old 10th January 2012, 11:41 PM   #745
DF96 is offline DF96  England
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Quote:
Originally Posted by tvrgeek
I agree if the very same energy profile is delivered to the motor,you will get the same response. Both the amp and the driver are complex impedances with short term energy storage. The driver has mechanical forces trying to return it to rest. The amp, the servo effect of the feedback trying to make the voltage match the signal. So, current will not be exactly 180 degrees off voltage at all times.
The same voltage to the same motor will deliver the "same energy profile", unless there is long term energy storage. I make no assumptions about the angle between voltage and current. Think of the amp as a voltage generator with a low but non-negligible output impedance - the impedance can even be non-linear. How it achieves this internally is irrelevant. Think of the speaker as a complex impedance, including short term energy storage. Now you could in principle have different amps producing the same voltage at the junction (=output terminals) by having different open circuit voltages but also different output impedances so the two changes exactly cancel, but then the same voltage is delivered to the load so the same sound will come out. In essence you have a potential divider, with the amp o/p Z at the top and the transducer at the bottom. If the voltage at the middle is the same then the current is the same, because it is flowing through the same lower impedance.

I think there is a confusion here, but I can't quite work out what it is. Always difficult to see inside someone else's head!
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Old 11th January 2012, 02:48 AM   #746
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Indeed!
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Old 11th January 2012, 07:21 AM   #747
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Folks,

Allow me to pose a few question, quite simple.

Given is:

1) An AP2 testset

2) A Resistor Load 4R

3) A Speaker Simulator Load as used by JA in stereophile

4) A Amplifier (DUT in the following)

The DUT is tested using the AP2 with any of the standard tests (THD&N, IMD, FR) and the tests show that the amplifiers output voltage is essentially an amplified replica of it's input with no measurable (by AP2) distortion and noise added and with a passband sufficiently wide to eliminate issues (phase, amplitude) in the audio band and is not affected by the loads used to test (listed above).

Questions:

please provide reasoning as to why the answer is as you answer, even though the questions themselves are simple are simple yes/no(/pass) type

1) With the AP2 Measurements as given above, do you consider this DUT to be "as near to perfect as possible"?

2) Do you feel any measurements not listed above, that is other than noise, harmonic distortion, intermodulation distortion, frequency response and load tolerance (damping factor); are required to make the determination in Question 1 and if yes, what are they?

3) Do the AP2 Measurements as given above inform us about about the actual performance of this amplifier when inserted into a real audio system?

4) Do the AP2 Measurements as given above inform us if the DUT when inserted into a HiFi Audio System will produce what is perceived by the majority of the potential customers "good sound" and would lead to a purchase of the DUT?

Ciao T
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Old 11th January 2012, 07:49 AM   #748
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Quote:
Originally Posted by ThorstenL View Post
[snip]

Questions:

please provide reasoning as to why the answer is as you answer, even though the questions themselves are simple are simple yes/no(/pass) type

1) With the AP2 Measurements as given above, do you consider this DUT to be "as near to perfect as possible"?
[snip]
Ciao T
Maybe time for me to come out
No. It will always be possible to design an amp with is 'more perfect' than the latest one. Matter of spending enough effort and money.

Quote:
Originally Posted by ThorstenL View Post
[snip]

2) Do you feel any measurements not listed above, that is other than noise, harmonic distortion, intermodulation distortion, frequency response and load tolerance (damping factor); are required to make the determination in Question 1 and if yes, what are they?
Yes. As said, it will always be possible engineering wise to build a 'better' amp and I expect that other measurements may be required to proof that one amp is better than another, but I have no specific answer as to which measurements this might be.

Quote:
Originally Posted by ThorstenL View Post
[snip]

3) Do the AP2 Measurements as given above inform us about about the actual performance of this amplifier when inserted into a real audio system?
Yes. Since the measurements inform us about how faithfull and transparant the DUT amplifies the input signal, that has a direct bearing on its performance in an audio system. The amp doesn't change when taken from a testbench into a system.

Quote:
Originally Posted by ThorstenL View Post
[snip]

4) Do the AP2 Measurements as given above inform us if the DUT when inserted into a HiFi Audio System will produce what is perceived by the majority of the potential customers "good sound" and would lead to a purchase of the DUT?

Ciao T
No. The perception of 'good sound' and eventual purchase decisions are based on a myriad of factors like physical shape and form, price, brand, marketing, reputation and several others, of which the actual, objective sound quality is just one. The diversity of the market of actual purchases, from Halcro though Parasound to Bose is proof of that.

hope this contributes,

jan
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Last edited by jan.didden; 11th January 2012 at 07:52 AM.
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Old 11th January 2012, 08:18 AM   #749
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Jan,

Quote:
Originally Posted by janneman View Post
Maybe time for me to come out
No. It will always be possible to design an amp with is 'more perfect' than the latest one. Matter of spending enough effort and money.
Just to be clear, my point was when tested using AP2 test the DUT does not add any HD or IMD the AP2 can measure and does not change it's bahviour using the specified loads.

So this Amp is at least as good as the AP2 or better. If you make a better amplifier how will you know?

Quote:
Originally Posted by janneman View Post
I expect that other measurements may be required to proof that one amp is better than another, but I have no specific answer as to which measurements this might be.
Hmm, so you position COULD be rendered as: "The listed measurements are insufficient, but I do not know in what way and what needs to be measured in addition to them"?

Quote:
Originally Posted by janneman View Post
Yes. Since the measurements inform us about how faithfull and transparant the DUT amplifies the input signal, that has a direct bearing on its performance in an audio system. The amp doesn't change when taken from a testbench into a system.
Jan, I included this question on purpose and I would suggest it actually bears some import and is worth reconsidering your answer. To focus this a little, sure, the amplifier does not change, but could it be perchance that it's environment change in ways that would influence the measured performance of the amplifier?

Quote:
Originally Posted by janneman View Post
No. The perception of 'good sound' and eventual purchase decisions are based on a myriad of factors like physical shape and form, price, brand, marketing, reputation and several others, of which the actual, objective sound quality is just one.
Okay, let us de-link "good sound" and "purchase decision", though I had good reasons to include it, as it in many ways at least in the audiophile context the ultimate arbiter, "will I trade what I have for this new gizmo at a financial loss to me".

In that case, however, let us remove the purchase decision and focus on "will it sound good?"

Ciao T
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Old 11th January 2012, 08:36 AM   #750
wahab is offline wahab  Algeria
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Quote:
Originally Posted by ThorstenL View Post
Jan, I included this question on purpose and I would suggest it actually bears some import and is worth reconsidering your answer. To focus this a little, sure, the amplifier does not change, but could it be perchance that it's environment change in ways that would influence the measured performance of the amplifier?
That is intellectual slight of hand...

Any wise engineer would also make environement testing , i.e , checking
stability and current capabilities for exemple , so your exemple is quite
irrelevant as it implies that the tester didnt check all necessary parameters
enough to make certainity that the amp is environment variation proof..

Indeed , there s a direct relation between how an amplifier measure
and how it sound , and in this respect , most amps , if not used
close to clipping , sound the same provided minimal care has been
done in the design and building.
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