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Old 6th February 2012, 10:57 PM   #5201
Salas is offline Salas  Greece
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Hmm, is the Is > Idss?
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Old 6th February 2012, 11:04 PM   #5202
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Very near, only degenerated by the 2,5Ohm. The stage is self conducting but also forced by the constant current sources. My sample of the FPS is quiet. When i get it back from a loan i can measure it. It simulated with -77dB against 1mV.
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Old 6th February 2012, 11:07 PM   #5203
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As a young man i worked in the High Tech industry. We would have build input stages for brain scanners that way. That was between 1984 and 1989.
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Old 6th February 2012, 11:12 PM   #5204
Salas is offline Salas  Greece
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I am a bit afraid about the forced current regarding the 1/f hyperinflation. Anyway, only when you will measure yours we can give hesener some solid landmark to work towards really. I like the simple concept there.
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Old 6th February 2012, 11:27 PM   #5205
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The FPS is basically a Tietze-Schenk low noise input stage, interpreted as a Fet input balanced INA. You can see it in T/S, Chap. 4 or in Burkhard Vogel´s "Sound of Silence", first Edition, page 48. John Curl send me a Fax with the same circuit from the 60th, also single ended, so this idea is ages old. A guy from Canada who´s name i have forgot made an ultra low noise single ended version although he is not a fan of the constant current sources. In praxis i found that the noise disadvantage is compensated by the gain advantage plus better PSSR. Two circuit i have in my lab prove that it is ultra low noise.
One is a single ended version with 4 x 2SK369. It is so quiet that Sam found it is more quiet then his line stage. The other is the AKSA Paris that has only one 2SK369 without source resistor at Idss. I have published measurements of both circuits before here.
I am absolutely sure that the constant current sources do no harm in noise IN THE CONFIGURATION I USE.
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Old 6th February 2012, 11:35 PM   #5206
Salas is offline Salas  Greece
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Must be something in the build that hesener will debug.
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Old 6th February 2012, 11:37 PM   #5207
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Yes, or he has not measured both inputs in tandem, balanced.
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Old 6th February 2012, 11:41 PM   #5208
ungie is offline ungie  Canada
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Once a GB is arranged, and I have one built up, I'll be publishing measurements using AP 2722 Cascade.
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Old 6th February 2012, 11:42 PM   #5209
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Great, that will show a lot.
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Old 7th February 2012, 12:58 AM   #5210
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I dug out a measurement of the Paris, taken at -50dB/U.
That was at the time i posted measurements from my professional lab. The Paris is in green and the noise floor of my measurement system in blue.
You can see the single ended non NFB nature by looking at the second harmonic. That grows in proportion with the input signal and ultimately third is coming up too ( not shown ).
This is a single selected 2SK369 on Idss without source resistor. It is bipolar cascoded with a ground referenced cacode with a 470 Ohm, 470 Ohm base divider, signal going out of the base ! This is supplied by a bipolar constant current source with an RC filtered single green Led voltage reference. The SAM has 4 x 2SK369 on a 0,8 Ohm feedback resistor. The current source is referenced by two red Led´s with RC filter so the emitter resistor can be of somewhat higher value. Sigurd simulated that a 100 Ohm resistor adds around 1dB noise, so for lowest noise it should be somewhat higher, say 220 Ohm. this is all well researched and proven in praxis. It works.
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File Type: jpg Paris -50dB Salas.jpg (114.7 KB, 264 views)
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