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Old 17th February 2012, 07:56 PM   #2571
dvv is offline dvv  Serbia
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Originally Posted by SY View Post
I understood that quite well. And as I said, this is no knock on your engineering abilities or your honesty or your sincerity, but rather on your ability to set up a properly controlled sensory test. There's no shame in that, not very many engineers do, it's not part of the training or the usual job duties. I certainly didn't learn any of that in school, had to pick it up the hard way from working in several industries where accurate, repeatable, and replicable data from sensory tests (haptic and organoleptic, in my case) were critical, and poorly designed or executed tests would put us out of business.

I would recommend again that you read through the little article in the last (Vol 2) issue of Linear Audio. It specifically deals with the sort of small-scale testing you were trying to do in your wire experiments.

Sy, I would be grateful if you quite simply listed the first five (5) mistakes you think we made. No lenghty explanations needed, just a list.

But my general comment stands as written. I will think long and hard before posting any shematic of what may be a simple auxilliray circuit, let alone anything more complex such as a power amp, lest I be jumped upon how it is theoretically badly concieved, how my values are impossible, and I'm pretty sure there would be somebody explaining to me how it couldn't possibly work, even if it's playing music in my room at that very moment.

Not to even mention "discussions" like why did you use that cr***y transistor and not xxxx, why just yy mA therough this trannie and not yy*+30% mA, those who "know" that those output devices don't have a hope in hell of sounding even decent, etc. I really hate back seat drivers. ESPECIALLY those who just glance at a schematic and know it all instantly. Maybe because I am really stupid and need at least a day to familiarize myself enough not to ask a really silly question, if I have one.
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Old 17th February 2012, 08:25 PM   #2572
SY is offline SY  United States
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Originally Posted by dvv View Post
Sy, I would be grateful if you quite simply listed the first five (5) mistakes you think we made. No lenghty explanations needed, just a list.
I'd recommend you read the Linear Audio article, then make your own list.

What stood out was a very unlikely score (I've run HUNDREDS of sensory panels, and your reported score for something you characterized as subtle is so unusual, it screams "poor controls"), and a complete absence of any mention of the details that would have taken the most effort to get right (e.g., level matching procedures, timing measurements and control, switching noise measurement and control, switching procedure, randomization of presentation, recording and scoring, isolation of the switching, randomization of controls...). Post hoc recollection is notoriously inaccurate- unless you video recorded the experiment, you will get the recounting of the details wrong.

I would repeat my advice to hire a good magician (if you can't afford a good experimental psychologist or sensory scientist) to help you set up your controls. That's the stuff that they're experts at and engineers aren't. Engineers and scientists are incredibly susceptible to being fooled and fooling themselves, much more so than most other people. Magicians LOVE having scientists for an audience.

Regarding your other comment, I've never hesitated to post my own circuits and schematics, but admittedly I'm not trying to sell or promote anything in audio and have benefited from the more intelligent criticisms.
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Old 17th February 2012, 08:49 PM   #2573
DF96 is offline DF96  England
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Originally Posted by dvv
But my general comment stands as written. I will think long and hard before posting any shematic of what may be a simple auxilliray circuit, let alone anything more complex such as a power amp, lest I be jumped upon how it is theoretically badly concieved, how my values are impossible, and I'm pretty sure there would be somebody explaining to me how it couldn't possibly work, even if it's playing music in my room at that very moment.
If you make a public statement you should not be surprised if you sometimes get public disagreement. It ought to be polite, but life is not always like that. The mods will prevent things from getting too out of hand. What you should not expect is that a design, however good or bad, will receive just praise (except from some quarters).

Quote:
Not to even mention "discussions" like why did you use that cr***y transistor and not xxxx, why just yy mA therough this trannie and not yy*+30% mA, those who "know" that those output devices don't have a hope in hell of sounding even decent, etc. I really hate back seat drivers. ESPECIALLY those who just glance at a schematic and know it all instantly.
Some people 'think' at the level of fashion statements, and confuse that with electronic design. They will criticise any circuit which does not use their favourite idea/bias point/components etc. You can ignore them if you wish.

There are others who really can look at a circuit and tell you that it won't work, based on sound engineering. If you think it does work, then it may be that you haven't actually built what you say you have built (surprisingly common - although you appear to know what you are doing), or it may be that the alleged problem does not appear in your environment. It may that your critics are wrong, in which case a reasonable argument can take place.

Please don't be put off. If you think you have got too strong a response then it probably means you have accidentally pushed someone's 'hot button' - most of us have them. Some of us could even tell you what some others' buttons are.
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Old 17th February 2012, 09:13 PM   #2574
bcarso is offline bcarso  United States
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Originally Posted by DF96 View Post
[snip] Internal frequencies in metals tend to be significantly higher than the audio band.
Front pastedown of Dunn tabulates fundamental constants and properties of materials at (roughly) 290 K. One item is the mean free time of electrons in copper, tau sub F: 2.4 * 10^-14 s.
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Old 17th February 2012, 09:34 PM   #2575
DF96 is offline DF96  England
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I seem to remember reading somewhere that one of the critical frequencies (I forget which one, I am not a solid state physicist) in copper is somewhere near the visible frequency range, which is why copper is opaque (but 'copper' colour) for visible light but transparent for UV. (Hope I got that right - working from memory - always dangerous!)
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Old 17th February 2012, 09:55 PM   #2576
tvrgeek is offline tvrgeek  United States
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Originally Posted by ThorstenL View Post
Hi,



Why?

As long as we do not need great lab-level accuracy (which we rarely do), it is simple to improvise current probes in more ways than I care to mention. Sniffer coils can be threaded upon transformer leadout wires, low value resistors connected in series (great to use with battery powered digital 'scopes) and so on...

Necessity is the mother of invention, not of capitulation...

Ciao T
I have made several attempts, not quite effective. Just enough to tease me. 30 gauge around little torrid, low value resistors. I have some ideas to build a little instrumentation amp for gain and try different perm doughnuts with much finer wire. It would be nice if I could find a published design. Otherwise, it is another distraction. I also wonder what king of amp the standard Tek probes need, as I see the probes for sale sans amps. I don't need the calibrated amp.

Would you care to mention a few ways? I'll divert for a couple of days.
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Old 17th February 2012, 10:11 PM   #2577
tvrgeek is offline tvrgeek  United States
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As I am making an order to MOuser and Digi-key this weekend, advice on specific ferrite doughnuts that would be suitable for AF current probe, please let me know.
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Old 17th February 2012, 10:39 PM   #2578
bcarso is offline bcarso  United States
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Originally Posted by tvrgeek View Post
[snip] I also wonder what king of amp the standard Tek probes need, as I see the probes for sale sans amps. I don't need the calibrated amp.
If it's the probe I'm thinking of, the "amp" is essential, the probe worthless without it. And you need the power supply that is part of that modular series.

Edit: this is the one I was thinking of, but it looks like it's been superseded for a while: http://www.testequity.com/products/569/

Edit again: By, for example, these: http://www.testequity.com/products/1113/

But you really probably don't need the d.c. capability.

Last edited by bcarso; 17th February 2012 at 10:46 PM.
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Old 18th February 2012, 12:08 AM   #2579
tvrgeek is offline tvrgeek  United States
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Yea, those are the ones I know from my old lab days. $3000. I see the probes for 99 bucks, and was wondering if I could build an amp for not too much. Probably not.
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Old 18th February 2012, 12:41 AM   #2580
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Tvr, you make so much of so little. There are 'creative' ways to measure current. You just have to use your innate intelligence to find something that might work in a specific situation.
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