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John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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Old 23rd July 2012, 04:25 PM   #24821
bcarso is offline bcarso  United States
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Originally Posted by scott wurcer View Post
...
Cheap R&D, I ground down the package on a grinding wheel, put it in a TEK op-amp curve tracer (remember those?) and called over the chief packaging engineer.
I used to slice the tops off of 2N4416s to allow photonic reset strategies in charge preamps. The interesting thing was how the chips were mounted, which translated into a greater or lesser volume of borosilicate glass surrounding the gate lead: TI had the chip sitting on the flat top of the gate lead, and others squashed the gate lead over the glass and put the chip on top. These latter parts were noticeably higher equivalent noise charge, I believe at least due in part to that detail of packaging.

Kern and Mackenzie at Bell Labs I believe were the first to identify the poor dielectric quality of the glass as responsible for a significant amount of charge noise in JFET preamps. They obtained chips to begin with and packaged them in low-loss headers, and got low noise results comparable to a group at Lawrence Berkeley despite not employing photonic reset. Of course the Berkeley group got a lot more publicity for their coolness factor.
 
Old 23rd July 2012, 04:26 PM   #24822
jacco vermeulen is offline jacco vermeulen  Netherlands
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Originally Posted by Wavebourn View Post
Engrish-101
Only rational that if things can be screwed up, they can also be screwed down.
 
Old 23rd July 2012, 04:29 PM   #24823
scott wurcer is online now scott wurcer  United States
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Originally Posted by RNMarsh View Post
I brought art back that are from well known artists but who never sell outside of China. What a great country and history. Oooops. back to electronics....
Interesting, Chinese brush painting is one of my hobbies. My teacher took us on a private tour of China (his wife is the daughter of one of chairman Mao's 4-star generals). The difference for the priveleged in China is rather amazing, one artist had a museum quality private collection of artifacts up to 6000yr. old. A second artist had a private compound that would shame many rich westerners. He painted huge (up to 12' X 16') bamboo and lotus paintings, would not fit in the overhead.

Over the last four years the fun of the trips to China has been waneing, as the westernization keeps progressing.
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"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."
 
Old 23rd July 2012, 04:31 PM   #24824
DF96 is offline DF96  England
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Originally Posted by hhoyt
Jitter of a CD pit-track is NEVER directly audible.
Please can we make it a condition of joining DIYaudio that people recite this until they believe it? And 'identical data' means precisely that: identical data.

And while I am here, can we get people to understand that short-term jitter and long-term frequency stability of a crystal oscillator are almost completely unrelated? Optimising one could degrade the other, if you are not careful.
 
Old 23rd July 2012, 04:39 PM   #24825
scott wurcer is online now scott wurcer  United States
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Originally Posted by bcarso View Post
Kern and Mackenzie at Bell Labs I believe were the first to identify the poor dielectric quality of the glass as responsible for a significant amount of charge noise in JFET preamps. They obtained chips to begin with and packaged them in low-loss headers, and got low noise results comparable to a group at Lawrence Berkeley despite not employing photonic reset. Of course the Berkeley group got a lot more publicity for their coolness factor.
Our biggest problem was crazing of the glass with poor handling, discovered in fixing a problem at Varian (vacuum guages for implanters). Was the charge noise DA or trapped impurities?

When the AD585 S&H was characterized it took weeks to find out that the 2pF package parasitic in parallel with the external cap had so much DA it dominated the error budget.
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"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."
 
Old 23rd July 2012, 04:41 PM   #24826
Wavebourn is offline Wavebourn  United States
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John Curl's Blowtorch preamplifier part II
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Originally Posted by jacco vermeulen View Post
Only rational that if things can be screwed up, they can also be screwed down.
What is the difference?
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Old 23rd July 2012, 04:42 PM   #24827
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by scott wurcer View Post
Interesting, Chinese brush painting is one of my hobbies. My teacher took us on a private tour of China (his wife is the daughter of one of chairman Mao's 4-star generals). The difference for the priveleged in China is rather amazing, one artist had a museum quality private collection of artifacts up to 6000yr. old. A second artist had a private compound that would shame many rich westerners. He painted huge (up to 12' X 16') bamboo and lotus paintings, would not fit in the overhead.

Over the last four years the fun of the trips to China has been waneing, as the westernization keeps progressing.
It helps to have the best conneections in china to see what there really is - the greatest works. Without that, there is no access. I want to get to Burma fast as central region has an airport now. The Thai tell me it will/is change fast now. Seems money rules. Money begets power and power begets control... the ultimate high after you have all the money you will ever need. :-( Looks like we are going the same way as in China the 1 and the 99%... big gap there. Did you buy any art to suppliment yur own work?
 
Old 23rd July 2012, 04:46 PM   #24828
RNMarsh is offline RNMarsh  United States
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Originally Posted by DF96 View Post
Please can we make it a condition of joining DIYaudio that people recite this until they believe it? And 'identical data' means precisely that: identical data.

And while I am here, can we get people to understand that short-term jitter and long-term frequency stability of a crystal oscillator are almost completely unrelated? Optimising one could degrade the other, if you are not careful.
Hear Hear.
[where where?]
There there.

I second the nomination.
 
Old 23rd July 2012, 05:07 PM   #24829
bcarso is offline bcarso  United States
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Originally Posted by scott wurcer View Post
Was the charge noise DA or trapped impurities?
Not sure.

After about a year, circa 1973, of believing poor sources (particularly, wrong information issuing from Princeton [horrors!]), I found the IEEE Transactions on Nuclear Science and a rich trove of charge amp material, which I adapted for the photodiode array preamps. Probably the preeminent guy was Veljko Radeka at Brookhaven, and he wrote some of the best papers on noise in charge preamps. He is still with us I believe and was honored not too long ago for his contributions.

But I don't recall his attribution of dielectric noise, specirfically, just the analysis of its effects.

Brad
 
Old 23rd July 2012, 05:21 PM   #24830
PMA is offline PMA  Europe
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Originally Posted by jneutron View Post
It may be the conductors around the device as opposed to the device itself.
I am not sure about this. The necessary condition is that the device is fixed to the heatsink, and the whole thing is most audible (resonates) at several kHz, close to 10 kHz.
 

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