The JC-2 preamp schematic on the website is wrong...Mr.John C? - Page 8 - diyAudio
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Old 25th September 2009, 04:45 PM   #71
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Default Jc-2 update

Quote:
Originally Posted by X.G. View Post
The JC-2 preamp Sch is on the famouse unoffical website of Mark Levinson

http://marklev.com/

After altering by another man from China,I just found the wrong in the ouput module sch.

http://www.hifidiy.com/dispbbs.asp?b...D=68247&skin=0

Click the image to open in full size.

In the ouput module(=line stage),the phase polarity of - input is same as the output.In the words,the feedback of this module is postive not negative,the output module is an OSC not a NFB amp.

To correct it,IMO,the base pin of 2N4401/2N4402 should be exchanged with the emitter pin.I wonder if anyone had rebuilded the JC-2 according to the marklev.com schematic.

Mr.John C and the other member,do you agree with me?

Thanks your any input.
The marlev.com guy got the scans from me several years ago, but he never published John Curl's correction labeled "JC-2 UPDATE" in The Audio Amateur.
Long discussions have been had, and much water has ran into the sea, but here it is attached.

Rolv-Karsten Rønningstad
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File Type: jpg JC-2 update by JC.jpg (44.3 KB, 870 views)
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Old 25th September 2009, 04:59 PM   #72
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Thanks for the input. R-K. I always get the leads confused, myself. However, what I first published was drawn up first at Mark Levenson, the company, and I didn't catch the error at first. Still, miss it today, if I don't look carefully. The correction came in a following issue of 'The Audio Amateur' and many people missed it, and still overlook it, even today.
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Old 25th September 2009, 05:15 PM   #73
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You're welcome, John!
I got these as copies of copies in the early 80ties. Your preamp was the Holy Grail, you know! So I built a copy, paid dearly for matched JFETs! But, I also had the Update, so my copies were correct. I even have the second one to this day. And also a ML-1, and in use.
Anyway, thank you for all your designs, and also writings at www.diyaudio.com.
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Old 26th September 2009, 09:20 AM   #74
HKC is offline HKC  Hong Kong
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What about modify JC-2 into balanced?

Click the image to open in full size.
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Old 26th September 2009, 10:13 AM   #75
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Default Balanced JC-2

Tell us more!
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Old 26th September 2009, 03:15 PM   #76
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What you really need is the JC-80 topology to effectively do balanced right.
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Old 26th September 2009, 03:54 PM   #77
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Click the image to open in full size.

Hi RK
It was an experiment using two JC-2 line stage pcbs I have available to form a one channel balanced pre-amp. Everybody was impressed even though the pre-amp was operated in one channel only.

Hi John
I did not have a chance to look at the JC-80 schematic. Is there any place I can locate it for a view?
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Old 26th September 2009, 04:14 PM   #78
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Aha
There are several ways to make a balanced driver; -1x amp on the normal + output, crosscupled feedback, or JC80 topology, etc
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Old 24th October 2013, 11:58 PM   #79
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Quote:
Originally Posted by HKC View Post
What about modify JC-2 into balanced?

Click the image to open in full size.
It is almost Halloween here in the US, so I don't feel too bad about reviving this zombie/old thread

Here is a JC-2 pre I just built with balanced XLR and RCA outputs. I call it the Cathedral 2-Eleven (I am not sure it will be a good idea to get to 7 ).
Attached Images
File Type: jpg DSC06412.jpg (318.0 KB, 85 views)
File Type: jpg DSC06431.jpg (400.2 KB, 90 views)
File Type: jpg DSC06466.jpg (265.3 KB, 80 views)
File Type: jpg DSC06493.jpg (377.5 KB, 104 views)
File Type: jpg DSC06501.JPG (334.5 KB, 93 views)
File Type: jpg DSC06483.jpg (290.2 KB, 49 views)
File Type: jpg DSC06485.jpg (302.4 KB, 59 views)
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Old 25th October 2013, 12:01 AM   #80
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Use the JC-80 technology, or if you are REALLY BRAVE, try the Parasound JC-2 topology. '-) P.S. It is easier just to buy one used.
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