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Simplistic NJFET RIAA
Simplistic NJFET RIAA
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Old 26th August 2012, 04:58 PM   #7891
vgeorge is offline vgeorge  Greece
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Simplistic NJFET RIAA
Found some 2SK369 on ebay. Do you think they are fakes?
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Old 26th August 2012, 05:01 PM   #7892
RCruz is offline RCruz  Switzerland
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Originally Posted by Bksabath View Post
Tanks Salas
I will go for 4 170 to try this out as soon as I got "litle" balanced phono finished
I take that Reflector is adequate
Reflektor is good, easy to build and a rock solid performer.
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Old 26th August 2012, 05:59 PM   #7893
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Originally Posted by vgeorge View Post
Found some 2SK369 on ebay. Do you think they are fakes?
Not as sought after as K170 bcs rarely specified they may stand a chance of being good. I would score the fewest to check out. If they are good they show a benefit in 1/F region. You can see on a chart that Scott Wurcer presented in 2010 when Patrick (EUVL) sent him some rare JFETs to shoot out. But they will not show the Vgs high enough for more than 0.5mV MC when considering low degeneration to keep the noise spec. Especially in folded cascode the swing can be the difference between VDS and VRload to ground only. Best is they are used for true low MC (DL103 or less) for good headroom.
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Old 26th August 2012, 07:19 PM   #7894
RCruz is offline RCruz  Switzerland
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Originally Posted by Salas View Post
Unipolar (FET) SE no global feedback, SIMPLE like a tube amp. JFETs are silky. SE no loop FB is big soundscape.
Will show you a folded cascode first stage (more PSRR) & optionally JFET cascoded 2nd stage with B1 style output buffer version, to test also when feeling adventurous. 2SK170 don't have the low 1/f that BJTs got. If you ever find some 2SK369 to parallel for front end let me know (will bring bass noise down). SE ain't DC coupled symmetric servo with FB, still a Vendetta type CCT is, and its still JFET front end, EB style is the same, that would be the sound style to put against symmetric BJT, and saves you the input offset.

I hope I gave some clues.

P.S. Last but not least normalize the SPL with a meter even, when comparing anything, each one pre normally has different gain.
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Yes, a different fruits typical case.
Its the transfer function each design conveys, we can't bolt something in judiciously over subjective qualities with any good guess.
The whys are for scientists much above our DIYer heads.
It does not show higher harmonics easily it takes much pushing.
It effects dynamics that shift overall impression though.
So there you have it, but no guarantee because I haven't evaluated it yet.
Juicy stuff

PS: what do you mean by CCT ?
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Old 26th August 2012, 07:22 PM   #7895
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Old 26th August 2012, 07:35 PM   #7896
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CirCuiT.
Thank you for your patience Salas
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Old 27th August 2012, 01:50 AM   #7897
Salas is offline Salas  Greece
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Originally Posted by Bksabath View Post
Got BL I will need to mesure them up but shuld be few sets at about 8ma

Mouser has 2SK170 from time to tyme and BF245 shuld be easier to came by
Ok, here it is for classic 4XK170BL. You may relax the matching for the quads since they are degenerated enough to share current at ~0.75*IDSS and the total transconductance (~130mS) will be steady for 7.5-9mA samples at shared ID. But make sure that the sum total of the quads IDSS between channels is nearly the same. So the folded cascodes will be sparing the same drive current to R16 and same gain. No loop feedback here to match the gain if not thorough with JFETs picking in both stages. It should present ~15 Ohm input equivalent noise resistance, not bad. And some better input headroom, adequate for normal MC also. Pick a ~5mA BF245A for Q8 and circa 15mA BF245C for Q5.
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Old 27th August 2012, 07:15 AM   #7898
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Tanks Salas
I am going to make the PCB and get started but is going to take a while as I got a couple of 72 hours weeks at work
I got same 2SK369 on their way hopefully they be the real thing and build as on post 7881

This new version has one less gain stage from the one I am using as I have the Low MC pre-pre I have enclosed the PDF it is based on here for reference.

So that is 4 Phono stages on my bench
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Old 27th August 2012, 08:09 AM   #7899
Salas is offline Salas  Greece
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Those new experiments have the gain due to folded cascode and higher total Yfs, skip pre-pre and one coupling for LMC, promise better input stage rail insulation because they refer their load resistor to ground, but they will not do HiMC, MM, they will not be modular, and it remains we like the twists. In case not, they can be readily reformed, no worries.
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Old 27th August 2012, 09:04 AM   #7900
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Those new experiments have the gain due to folded cascode and higher total Yfs, skip pre-pre and one coupling for LMC, promise better input stage rail insulation because they refer their load resistor to ground, but they will not do HiMC, MM, they will not be modular, and it remains we like the twists. In case not, they can be readily reformed, no worries.
As load resistor is refered to GND, this means current flows inversely in Q3.

Output impedance of first stage is 2k2r right ?
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