The JC-2 preamp schematic on the website is wrong...Mr.John C?

[Variac]

I missed the "sound check" concert when they first tried this system out at the Cow Palace near San Francisco, in a (very) rare occurance of academic responsibility. Sure regret it now!!

I'm not sure I ever heard the full setup. They used pieces of it for years after I think.
My memories are kinda fuzzy...........................😉

 

[Bo Hansén]

I don´t know if I remember right, but I think a Mr. Meyer was involved in this speaker set up and the differential mikes.

--Bo

 

[GRollins]

Ron Wickersham should have been in the mix somewhere, yes?

Grey

 

[john curl]

Ron Wickersham, Bear and I had the responsibility for the components of the system. There were others as well. Jon Meyer was a personal friend to me, but he did not work with this system. Later, Jon Meyer and I went to Switzerland to work on another project, and this system was completed by Ron Wickersham.

 

[Bo Hansén]

Thank´s John,

Always nice to hear the storry from the sourse.

-Bo

 

[john curl]

Another small fact. The circuit that we were originally talking about on this thread that came from the JC-2, was originally designed for the big 'Wall of Sound' system used by the Grateful Dead. Mark adopted it for the JC-2 because of its success with the Grateful Dead in sounding better than selected existing op-amps.

 

[johnferrier]

The "Wall of Sound"

John Curl happen to be in this pic???

 

[HKC]

I can't remember. It has been 30 years. With class A output bias of about 50 ma, it can be pretty good, however.

Mr. Curl

I set the current of my JC-2 clone output @ 50ma but how about the current @ the differential JFet input stage? If I remember right you said 6ma. Please advice.

Best Regards

 

[john curl]

Please don't worry too much. The input Iq will be whatever it takes to get 50 ma from the output devices.

 

[HKC]

Mr. Curl

Thank you for your prompt reply.
With this answer I have nothing to worry about now.

Best Regards

 

[R-K Rønningstad]

Jc-2 update

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?boardID=13&RootID=68247&ID=68247&skin=0

An externally hosted image should be here but it was not working when we last tested it.

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

 

[john curl]

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.

 

[R-K Rønningstad]

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. 🙂

 

[HKC]

What about modify JC-2 into balanced?

 

[R-K Rønningstad]

Balanced JC-2

Tell us more!

 

[john curl]

What you really need is the JC-80 topology to effectively do balanced right.

 

[HKC]

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?

 

[R-K Rønningstad]

Aha
There are several ways to make a balanced driver; -1x amp on the normal + output, crosscupled feedback, or JC80 topology, etc

 

[whaleman]

What about modify JC-2 into balanced?

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 ).

 

[john curl]

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.