John Curl's Blowtorch preamplifier part II - Page 3881 - diyAudio
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Old 1st May 2013, 08:09 PM   #38801
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Quote:
Originally Posted by bcarso View Post
I pulled out my copy of Sze, Physics of Semiconductor Devices, early this AM to see a bit more about Schottky and others, and in particular to make sure there weren't two of them (the shot noise one and the diode one). What was fascinating was the theory of the rectifying metal-semiconductor junction, and the references and some resemblance to thermionic emission. Sze is great by the way, although a bit out-of-date understandably --- but one of those "if you have only one book..." I suppose by now there may be a later edition that the second that I have.
Wow...there was a second edition?? Mine's from '69

jn
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Old 1st May 2013, 08:11 PM   #38802
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Originally Posted by Waly View Post
That would be the excess noise, otherwise 1/f noise is generated in any condensed matter system, that's what I was taught in the solid state physics course. Or perhaps it's the high 1/f corner frequency which is very high in tubes?
Yes, it is excess in the sense that no one has satisfactorily modeled it as a physical mechanism, although there are perennial assaults on the fortress. Maybe some day. One physicist friend believed that 1/f phenomena were indeed limited in low-frequency extension, but the time constant would turn out to be the age of the universe

And yes, in tubes the corner does seem to remain stubbornly high frequency, and still difficult to predict. I think there is a recent piece in Linear Audio (?) in which the author, after running down various things known, winds up saying you have to test and optimize the operating point for any specific tube sample to get the lowest noise. There are some remarks in Cherry and Hooper about the dependence being to some extent one of noise proportional to anode current, which may represent an uncomfortable tradeoff in a given circuit.

Another option that is unlikely anyone will fund, but was explored many years ago for other purposes: an optoelectronic cold cathode. I don't recall if the results of the experimental devices had reduced 1/f noise or not.
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Old 1st May 2013, 08:12 PM   #38803
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There's a Third, but it looks to be over my head:

Physics of Semiconductor Devices: Simon M. Sze, Kwok K. Ng: 9780471143239: Amazon.com: Books

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Chris
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Old 1st May 2013, 08:12 PM   #38804
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Sorry, here is the next page:
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Old 1st May 2013, 08:14 PM   #38805
bcarso is offline bcarso  United States
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Originally Posted by jneutron View Post
Wow...there was a second edition?? Mine's from '69

jn
My copy was about as well-hidden in a storage box as to make me think I had lost it somehow, and I had the first edition accessible, but yes, it finally was unearthed. The second edition dates from 1981: ISBN 0471056618

EDIT 1: Ah yes thanks Chris. I guess I had seen that third ed. in a search, as it was clearly a transitional one with the co-author. Sze, born in 1936, could well be graced with a collaborator now.

EDIT 2: Just ordered for about 77 bucks and shipping. We shall see. What is interesting sometimes is what gets left out from previous editions of things. It was disappointing that latest editions of Gray and Meyer (et al.) don't barely even acknowledge JFETs, for example. So one does not want to throw old editions away, many times.

Last edited by bcarso; 1st May 2013 at 08:23 PM.
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Old 1st May 2013, 08:32 PM   #38806
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Straying from the well defined, one thing that vacuum valves have, and modern devices usually have not, is wasteful profligacy. Lots of heat, lots of electrons, "headroom" of another sort. JC recommends running his output devices at 30 or 50mA, when less than 5mA would drive anticipated loads - so who knows? We're complex pieces of mud.

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Chris
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Old 1st May 2013, 08:50 PM   #38807
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so who knows? We're complex pieces of mud.

Thanks,
Chris
Speak for yourself.

I'm not complex.

jn
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Old 1st May 2013, 09:01 PM   #38808
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Speak for yourself.

I'm not complex.
Arf! I read somewhere recently that our processing speed is 126 bits per second. "Truth? You (literally) can't handle the truth!" Frogs can only "see" four things: a horizontal line, a flying insect, a snake, and something else (?). We must be some variation on that theme.

Thanks, as always,
Chris
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Old 1st May 2013, 09:11 PM   #38809
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We spent many man-years in an effort to REMOVE the transformer from audio circuitry. .
Your loss.

se
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Old 1st May 2013, 09:56 PM   #38810
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Originally Posted by bcarso View Post
Yes, it is excess in the sense that no one has satisfactorily modeled it as a physical mechanism, although there are perennial assaults on the fortress.
This may lead to some confusion with regard how excess noise is used with regard to resistors. In that case, it is related to current, and some of the mechanisms involved are well understood (e.g. granular structure of carbon composites, impefections in metal films). The fact that resistor excess noise also has a 1/f character is just the way nature works. Better find a better term to describe the tube case.
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