http://www.diyaudio.com/forums/solid-state/161155-solid-state-testing-tug-war-2.html
I really can't see why this is thought to be such a "obscure" - "ignored by conventional engineering" topic
Self, Cordell's books seem like they could be reasonable beginning summarys what is understood by "conventional engineering" - for dealing with "complex" loudspeaker loads, estimates of the peak currents are given, guidance for current "reserve", choosing Q, topology, sizing outputs to avoid "beta droop"
beginning feedback amp courses quickly introduce Bode's sensitivity analysis tools - specifically to address these questions
the simplest view is that you are "measuring" the output Z of the amp, for high loop gain feedback amps this can be ~10 uOhm over the audio frquency range - any "effect" is going to be ~ Zout/Zload ~= -100 dB for typical dynamic loudspeakers where there is enough gain, ouput current capbility
the Cherry paper's conclusion was that distortion for output injected current swing is less than or equal to the distortion of the amp driving the output to the same current levels in "forward" operation
I really can't see why this is thought to be such a "obscure" - "ignored by conventional engineering" topic
Self, Cordell's books seem like they could be reasonable beginning summarys what is understood by "conventional engineering" - for dealing with "complex" loudspeaker loads, estimates of the peak currents are given, guidance for current "reserve", choosing Q, topology, sizing outputs to avoid "beta droop"
beginning feedback amp courses quickly introduce Bode's sensitivity analysis tools - specifically to address these questions
the simplest view is that you are "measuring" the output Z of the amp, for high loop gain feedback amps this can be ~10 uOhm over the audio frquency range - any "effect" is going to be ~ Zout/Zload ~= -100 dB for typical dynamic loudspeakers where there is enough gain, ouput current capbility
the Cherry paper's conclusion was that distortion for output injected current swing is less than or equal to the distortion of the amp driving the output to the same current levels in "forward" operation
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So my other thought was to a-b the 8 ohm resistor with say a 7inch focal coil mid woofer; could be interesting to see if the " 1/DF nulled" signal & channel B distortion was at all audible.
Hi Folks,
Nearly 200 Posts ago I posed some very precise and topical questions, which if answered directly and to ones best knowledge would clearly illustrate the positions in this thread and would allow these positions to be falsified or accepted based on current knowledge and/or the proofs provided with them:
Sound Quality Vs. Measurements - Thorstens Four Questions post
I have noticed that only two posters have taken the time to even consider these questions in their entirety and then the comments where imprecise with answers which where framed so that in fact no specific position was taken and the questions where not answered at all.
I find this disappointing, as we have enough people here who normally have no problem to express their opinions and positions on what has been distilled into these four questions.
Perhaps it is that everyone expects a trap, by which the unreasoning subjectivist conspiracy is trying to trick them into admitting something they do not wish to admit?
Rest assured, the questions ask precisely what they ask and I already have agreed to modify question #4 to remove the tie in between "good sound" and "purchase decision".
So I would again ask all that have contributed to this thread to take a stand, be counted, make clear their positions and open these positions up to acceptance or falsification.
Otherwise we continue to have the same pointless argument again, all over again and with no resolution or improvement to the situation, meaning we all have wasted our time in this thread. Here again the questions with minor corrections to address criticism from posters about their precision, underlined sections are added later to produce more clarity.
Ciao T
Nearly 200 Posts ago I posed some very precise and topical questions, which if answered directly and to ones best knowledge would clearly illustrate the positions in this thread and would allow these positions to be falsified or accepted based on current knowledge and/or the proofs provided with them:
Sound Quality Vs. Measurements - Thorstens Four Questions post
I have noticed that only two posters have taken the time to even consider these questions in their entirety and then the comments where imprecise with answers which where framed so that in fact no specific position was taken and the questions where not answered at all.
I find this disappointing, as we have enough people here who normally have no problem to express their opinions and positions on what has been distilled into these four questions.
Perhaps it is that everyone expects a trap, by which the unreasoning subjectivist conspiracy is trying to trick them into admitting something they do not wish to admit?
Rest assured, the questions ask precisely what they ask and I already have agreed to modify question #4 to remove the tie in between "good sound" and "purchase decision".
So I would again ask all that have contributed to this thread to take a stand, be counted, make clear their positions and open these positions up to acceptance or falsification.
Otherwise we continue to have the same pointless argument again, all over again and with no resolution or improvement to the situation, meaning we all have wasted our time in this thread. Here again the questions with minor corrections to address criticism from posters about their precision, underlined sections are added later to produce more clarity.
Ciao T
Re Thorsten's four questions.
Surely there should be other qualifications such as the choice of weave of the interconnecting leads, composition of conductors and such. Otherwise the test is implying that such items have no effect whatsoever on sound quality. And they very clearly do... don't they? Does the AP2 employ digital sampling, high levels of feedback/high open loop gain, class D type techniques within its ADCs, DACs and measurement circuits? If so, then you'd presumably be happy to use such techniques in building an amplifier. But if you believe that even a mic pre-amp has a 'sound', then surely you could never ever pay even the slightest attention to an AP2 indicating 'perfection'.
Personally, I'd be inclined to believe that the DUT will sound great - unless it looks awful, in which case my mind will tell me that it sounds awful.
(Edit) And there is also the question I asked a few hundred posts ago: Could you design an amplifier to pass all 'conventional' tests with flying colours, but that sounded awful? I'm pretty confident that if I knew all the tests an AP2 is capable of, I could do it.
Surely there should be other qualifications such as the choice of weave of the interconnecting leads, composition of conductors and such. Otherwise the test is implying that such items have no effect whatsoever on sound quality. And they very clearly do... don't they? Does the AP2 employ digital sampling, high levels of feedback/high open loop gain, class D type techniques within its ADCs, DACs and measurement circuits? If so, then you'd presumably be happy to use such techniques in building an amplifier. But if you believe that even a mic pre-amp has a 'sound', then surely you could never ever pay even the slightest attention to an AP2 indicating 'perfection'.
Personally, I'd be inclined to believe that the DUT will sound great - unless it looks awful, in which case my mind will tell me that it sounds awful.
(Edit) And there is also the question I asked a few hundred posts ago: Could you design an amplifier to pass all 'conventional' tests with flying colours, but that sounded awful? I'm pretty confident that if I knew all the tests an AP2 is capable of, I could do it.
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Yes, you are likely to be missing input stage common-mode distortion and VAS voltage swing distortion. Maybe feedback resistor distortion too. So unless there is some cancellation in the normal mode of use, this test would give lower levels of distortion. Output impedance nonlinearity is a useful thing to know.jcx said:
From you, Thorsten, with your habit of politely, carefully and accurately restating your opponent's position before begging to differ? Surely not!ThorstenL said:
Thorsten's 4 questions:
1) Not possible to tell with the information given. 'Near to perfect' to me means 'near to perfectly transparent' not 'near to perfect traditional measurements'.
2) No known set of measurements approaches unity correlation with transparency. For suggestions about getting closer see my earlier posting on this thread.
3) Most certainly not - the AP2 only tests in diff mode, not common-mode. (Note to Jan - not thinking CMRR setting on AP2 here ok?)
4) I doubt it very much. But presumably a cloth-eared set of potential customers could be pre-selected to achieve that result if desired.
1) Not possible to tell with the information given. 'Near to perfect' to me means 'near to perfectly transparent' not 'near to perfect traditional measurements'.
2) No known set of measurements approaches unity correlation with transparency. For suggestions about getting closer see my earlier posting on this thread.
3) Most certainly not - the AP2 only tests in diff mode, not common-mode. (Note to Jan - not thinking CMRR setting on AP2 here ok?)
4) I doubt it very much. But presumably a cloth-eared set of potential customers could be pre-selected to achieve that result if desired.
Do you have a larger scan or a link to this article ? It´s hard to understand with this small section what exactly is the procedure.
And irreligious people don't have answers to anything? Why should it be surprising if peoples' thoughts and opinions relate to their world view? We see it on here with audio debates: people starting from different positions often tend to end up in different positions, even though they all sincerely believe they are merely following the clear evidence set before them.
PS Oops, sorry, mod - delet this post if you like.
PS Oops, sorry, mod - delet this post if you like.
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You've gotten a very clear answer in the lack of answers. What's hard to understand about that?
Thorsten,
Well given that a lot of "white box" testing went in to the development in order to achieve such extraordinary "black box" goals, and assuming that these additional tests included stability and clipping behavior. And that the Amp was within a reasonable dynamic power level, then:
1) Very likely yes, especially since I can perform any AP2 measurements including various stressing 2 tone responses.
2) I would like to explicitly add stability verification (for a wider range of loads) and various burst response verification tests for ac effects.
3) Yes, with the understanding that the Amp still operates in the real system as on the test bench. That is no oscillations, added noise, or ground loops are
introduced in the process.
4) Absolutely, with the marketing claim of "Best Measured Amp Ever".
Thanks
-Antonio
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