John Curl's Blowtorch preamplifier part II - Page 2090 - diyAudio
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Old 28th February 2012, 01:46 AM   #20891
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Originally Posted by SY View Post
Even not-so-modern. You can use an interferometric method to get positional resolution of 150nm with a red laser, and with a quadrature setup, you know velocity; this was routinely done in spectrometers in the '70s. I started to play with that for a subwoofer servo, but ran into some issues with having some of the optics prototyped affordably.
Or how about a linear actuator kept an exact distance away by a nulled optical position sensor?
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Old 28th February 2012, 01:52 AM   #20892
SY is offline SY  United States
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How do you keep track of the fringes? There must be thousands in the throw of some woofers.
Yup, but it's easy to count thousands. You would have to ignore the uncertainty in the rest position, but if you have the fringes, you know the velocity, and the quadrature beam gives you the direction. Standard stuff in FTIR spectrometers, where the throws are easily woofer-scale for high res measurement. The Nicolet 60SX I used to play with ran a heavy mirror a centimeter back and forth at 85 Hz.
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Old 28th February 2012, 02:28 AM   #20893
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I can't remember him discussing feed-forward at any time with me.
OK he wasn't feedforward negative as it were... Having said that I have very great respect for Heyser, and saddened that he left. I would love to have known him, let alone heard what he heard.
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Old 28th February 2012, 02:40 AM   #20894
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You should study his early papers. The best is jaes preprint 91, given oct. 1959. This was when he formed his opinion about negative feedback.

Last edited by john curl; 28th February 2012 at 02:46 AM.
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Old 28th February 2012, 12:50 PM   #20895
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Originally Posted by scott wurcer View Post
I thought the convention for current flow was established before anyone knew about electrons.
Yup. Kite flying geek..

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Old 28th February 2012, 02:47 PM   #20896
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I thought the convention for current flow was established before anyone knew about electrons.
It was based on observations of spark movement. And if you care to try it sparks do move from plus to minus!

As to interferometry, Many years back I was visiting Bose, one of the stops on the tour was supposed to be their laser lab. They had brought in a world class fellow to set it up so they could look at their drivers. I mention I was anxious to see it as I had worked with optical systems. They took it off the tour because they considered it "Secret" and so would not show it to anyone who might actually learn something.

Then decades later I was at JBL in the their large testing room, waiting for my friends to come back from a not so quick bathroom break. One of their engineers who did not know me wandered in and stood around looking nervous. He wanted to measure the deflection of an enclosure, but did not want to do it in front of me, as he though it was "Secret" stuff. My buddies got back and laughingly explained that it was OK to do it in front of me as they had just been demonstrating that system to me.

These days you just buy a Klippel analyzer. It is a nice and moderately priced system.
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Old 28th February 2012, 03:30 PM   #20897
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Hi,

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Originally Posted by bcarso View Post
I have seen audiophiles sniff at balanced and disparage push-pull, and I can only try to make my own judgments.
There is nothing wrong per se, with balanced. However, if you do it Pro-Style it means using transformers or complex balanced driver/receiver circuits to replace transformers.

This lead to high end audio adopting designs that are in fact balanced, but what I call "opposite polarity dual single ended", or "high end pseudo-balanced" would be a better or at least more pithy term.

Typically "high end pseudo-balanced" gear has abysmal CMRR, and "balance", so they effectively negate any benefits of balanced signal transmission.

Some may argue that distortion is reduced. This applies only to THD and/or even order harmonics though, so while MEASURED distortion is reduced, AUDIBLE distortion is usually increased. Some may argue that PSU AC Load is reduced, this is true for pure class A circuitry only and with respect, unless your CMRR and "balance" is really choodessny horrorshow, scratch that...

Hence you end up using double the number of parts to get a performance that usually is worse than decent single ended circuitry for halve the money. Or you use SE Circuitry and add transformers (which are against some people's religion), complex multi-op-amp drivers and receivers (which are against some other people's religion), but that also blows your budget and RARELY directly improves sound quality or objective performance (it may do so indirectly).

Another way of looking at it, for the same budget I can always make WAY BETTER single ended circuitry than "high end pseudo-balanced" or true "pro-balanced".

Ciao T
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Old 28th February 2012, 03:39 PM   #20898
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John,

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Originally Posted by john curl View Post
Black found it a real problem, so he invented electronic negative feedback to replace it.
Electronic negative feedback in basically the way Black applied it was patented in the 1924 by Paul Gustavus Adolphus Helmut Voigt (a German living in Britain). Thus his application of looped feedback antedates Black by three years. He also already had the foresight to enclose the "Sounder" (Speaker) in the feedback loop.

This is not to suggest anything untoward on the part of Black, just parallel development. Of course Black had a better publicity department.

Ciao T
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Old 28th February 2012, 04:15 PM   #20899
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T, this is a problem between countries. EVERY country likes to publicize its own inventor. The Germans, the Russians, the British and the Americans do this all the time.
American children are told that Edison invented the light bulb, for example, leaving Swan and others out of the effort.
IF you read what Harold Black did, in his own words, you cannot help but admire him. He had to keep his findings away from Bode and others, because he KNEW they would try to take credit for it, and so they did to some degree in future years.
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Old 28th February 2012, 04:24 PM   #20900
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Ed, when I worked as a consultant for JBL in 1977-8, I remember how they got very excited over laser measurements. My personal opinion was that they should revise their basic horn designs to reduce horn throat distortion and other problems, rather than play with a new 'toy'.
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