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Old 12th May 2013, 10:48 PM   #2191
quan is online now quan  Australia
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Quote:
Originally Posted by hesener View Post
hi quan, sorry I didnt make pictures from the underside (and they would not look beautiful....). But I am considering a layout and will post pictures hopefully soon...
stay tuned, and enjoy the current buffer which is very good too
Thanks Alfred, this hobby is nervereding is it.
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Old 12th May 2013, 10:56 PM   #2192
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Nice to have seen you guys at the High End.
I am back in the hotel and drive home on monday.
Sorry, i did not find the time to post the last days.
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Old 13th May 2013, 07:53 PM   #2193
Marra is online now Marra  United Kingdom
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Finally my Paradise has a home.Now for some serious listening.

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Old 13th May 2013, 08:07 PM   #2194
FdW is offline FdW  Netherlands
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Have fun listening? it looks great!
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Old 13th May 2013, 10:30 PM   #2195
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Yes, well done. I hope you like it.
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Old 14th May 2013, 05:41 PM   #2196
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It is really a pleasure to work with these PCB's ... I enjoy every single step in the build

Not very sure though about matching of the J310 in the output buffer. As I haven't read about them in the guide, I could assume I can pick them straight out of the bag. Still I remember reading some directions from Joachim or Alfred, but can't get that post. Should I get them with Vp bigger than 3V if I remember correctly? I have a custom matching device and I get in my batch only very few transistor with Vp bigger than 3 V (I know, actually it is negative, so it should be lower than -3V).

i suppose this rationale should apply only for the upper J310, that works as a cascoded voltage controlled current source with 2SK170. And the idea should be to offer sufficient voltage for 2SK170, also if I remember correctly.

I know, everybody is excited about the new old Calvin buffer but it will be highly appreciated if someone can point me to that post, or if somebody can bring more details to the requirements of the J310 parameters in the old/new output buffer
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Old 14th May 2013, 09:05 PM   #2197
hesener is offline hesener  Germany
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Hi metallicus69, the actual VTH of the J310s is not very important, values between 2.5V to 3V are just fine. Ideally, the upper and lower transistor should be roughly the same but it doesnt matter much.
The thresholds of the 2SK170s matter more, they should be close. If they are not, the buffer will exhibit a DC offset voltage, measurable between "RIAA EXT" connector and the output connector. But, the servo will regulate that away no problem.

hope that helps!
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Old 14th May 2013, 09:35 PM   #2198
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Thanks hesener, it helps indeed!
In the end I picked enough J310 with Vp around 3V (+/- 10mV).
What is confusing in your post is "thresholds of the 2SK170s", as this is only one in that stage. What exactly is important in those thresholds? (related to J310?)
I imagined that the servo will take care of reasonable amounts of parameters spread, but I prefer that it's doing less work. For this, I matched everything very tight (also between channels), and even the input and mirror transistors will be thermally coupled and as much as possible isolated from the air movements (I hope).
Only this output buffer gave me some question marks regarding the way I should pick/match the correct components/pairs but if it's not very important, I will try to pick the pairs between channels (close Idss for 2SK170BLs). I will explore the Calvin buffer for sure in the future, but as of now, I will build it as it is.
Cheers!
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Old 14th May 2013, 09:55 PM   #2199
hesener is offline hesener  Germany
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of course you are right, sorry for the oversight. yes there is only one SK170, and its IDSS should match the ID of the J310 "degenerated" by R15. So if the output offset is not what it should be, adjusting R15 should get you there.
But with what you describe here you should be fine....
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Old 14th May 2013, 10:24 PM   #2200
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No worries, it makes more sense now! Thanks for support!
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