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UDNeSS, or You don't need Semisouth's
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Old 25th September 2019, 08:08 PM   #1
EUVL is offline EUVL  Europe
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Default UDNeSS, or You don't need Semisouth's

There is quite a bit of excitement recently about the unobtanium Semisouth SJEP120R100 power JFETs
that Nelson Pass uses in his First Watt products, such as the mysterious J2.
So much so, that the prices on ebay went up by 67% in one weekend.

If only as an attempt to provide an alternative, I promised to post something similar but without any unobtaniums.
SJEP120R100 on ebay: are these the real thing?
(Post #22)

So here you are. I am quite surprised myself that it came out so well, even if only in simulation.


Happy reading,
Patrick

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Attached Files
File Type: pdf UDNeSS Public 190925.pdf (572.4 KB, 1558 views)
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Last edited by EUVL; 26th September 2019 at 04:50 AM.
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Old 25th September 2019, 08:32 PM   #2
EUVL is offline EUVL  Europe
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A spice file to play with.


Patrick

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File Type: asc UDNeSS V1 Public THD.asc (4.4 KB, 213 views)
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Old 25th September 2019, 08:45 PM   #3
Dennis Hui is offline Dennis Hui  Canada
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UDNeSS, or You don't need Semisouth's
Very nice! Thank you Patrick.

Dennis
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Old 25th September 2019, 08:48 PM   #4
blackdod is offline blackdod  Europe
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Thanks Patrick.
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Old 25th September 2019, 11:05 PM   #5
gary s is offline gary s  Australia
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Thanks Patrick, any thoughts of someone producing a suitable PCB design for the circuits and turning them into a group buy. I think you will get a lot of interest, especially from those that might miss out on the Semisouth GB.
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Old 26th September 2019, 02:38 AM   #6
indra1 is offline indra1  Indonesia
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Seems the phase of Udness 2H is ~180 to the SJJ.
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Old 26th September 2019, 03:08 AM   #7
dBel84 is offline dBel84  United States
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Love the name!
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Old 26th September 2019, 04:49 AM   #8
EUVL is offline EUVL  Europe
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Even if you have Semisouth's, I think this is still a very good exercise before an SJJ.

I'll publish Gerber files for the UDNeSS perhaps in a week.
35Ám double sided, within 10x10cm.
Same as the SJJ published at the Pass forum.
I'll let you figure out how to hard wire parallel FETs by P2P for the ProUDNeSS.

I have not built. We don't have US FETs in stock.
So be warned.


Patrick
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Old 26th September 2019, 05:06 AM   #9
EUVL is offline EUVL  Europe
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As to the phase of the second harmonics, I quote Nelson in his article :
http://www.firstwatt.com/pdf/art_h2.pdf

"So why is the phase important?
Well, it's a subtle thing. I don't suppose everyone can hear it, and fewer particularly care,
but from listening tests we learn that there is a tendency to interpret negative phase 2nd as giving a deeper soundstage
and improved localization than otherwise.
Positive phase seems to put the instruments and vocals closer and a little more in-your-face with enhanced detail.
Your results may vary .....
Roughly speaking, listeners tended to prefer about 1% negative phase 2nd harmonic...."

By sheer chance, the H2 of the UDNeSS is negative phase.


Patrick
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Old 26th September 2019, 06:49 AM   #10
indra1 is offline indra1  Indonesia
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Quote:
Originally Posted by EUVL View Post
... By sheer chance, the H2 of the UDNeSS is negative phase...
My sim indicates otherwise, please reconfirm. Ltspice seems to show inconsistent sign on phase of H2, correct on inverting circuit but shifted 180 on non inverting. I used Distortion_residual.asc from Spice simulation thread post #361 attachment.
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File Type: gif Udness residual.gif (10.5 KB, 2858 views)
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