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Old 21st January 2003, 05:46 AM   #1
HKC is offline HKC  Hong Kong
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Default Need to build JC 2 preamp

Hello Folks

I am prepare to build John Curl's JC2 preamp. However I am not electronic expert. I do not know the purpose of the 100R trim pot in the phono stage and the 500R trim pot in the ling stage. Does anyone can help to tell me the purpose & how to adjust these trim pots to get the best performance of this preamp circuit?

Thanks
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Old 21st January 2003, 06:39 AM   #2
halojoy is offline halojoy  Sweden
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Default Re: Need to build JC 2 preamp

Quote:
Originally posted by HKC
Hello Folks

I am prepare to build John Curl's JC2 preamp. However I am not electronic expert. I do not know the purpose of the 100R trim pot in the phono stage and the 500R trim pot in the ling stage. Does anyone can help to tell me the purpose & how to adjust these trim pots to get the best performance of this preamp circuit?

Thanks
Does anybody have a schematic.
at least a clip of that part, where the trimpot is.

Thanks - will make it 10 times easier to give some advice to you

/halo - according to ElsoKwak halojoy is "A Fan of John Curl"
- well, not exactly
- halo is even more of "A Fan of Elso's Work on Digital Timing"
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Old 21st January 2003, 07:22 AM   #3
HKC is offline HKC  Hong Kong
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Default Need to build JC2 preamp

Hello Halojoy

The schmetic is here:

http://marklev.com

Please take a look

Thanks
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Old 21st January 2003, 07:50 AM   #4
halojoy is offline halojoy  Sweden
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Default Re: Need to build JC2 preamp

Quote:
Originally posted by HKC
Hello Halojoy
The schmetic is here:

http://marklev.com

Please take a look
Thanks
Thanks HKC

I and and several other guys
will have a look.

Soon you will get some nice answers!

not necessary by
/halojoy
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Old 21st January 2003, 07:52 AM   #5
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Lightbulb Remake of John Curls JC-2

Hi HKC,
Rather than trying to rebuild a JC-2 may I suggest to build something more "modern" like Sonny Andersons circuit. This easely surpasses the JC-2 in soundquality.

Jfet/bipolar PCB and Schematic (finaly)

Quite a few of the FETs and transistors for the JC-2 are no longer available. Also a monolitic dual sounds much better than a handmatched FET.
The 500 Ohm pot in the line amp sets the quiescent current of the inputstage and the 100 Ohm pot in the phono the offset.
Please note that the linemodules in real world have two pots. One is controlling the offset but not shown in the schematic.
I believe the schematic is a very crude and early one. I opened some defective modules with boiling antifreeze. (ates away the epoxy a bit) and found MPSU05 and MPSU56 outputtransistors in the modules, NOT FET's. (Also obsolete tranasistors) Also the line amp is slightly more complicated. And input FETs were 2N4392 and 2N5115 (metalcan).

halojoy, Thanks for the kind words. Did you receive my email regarding the Denesson JC-80 made by John Curl?
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Old 21st January 2003, 08:03 AM   #6
halojoy is offline halojoy  Sweden
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Arrow this is halo promoting halojoy

Quote:
Originally posted by halojoy

Does anybody have a schematic.
at least a clip of that part, where the trimpot is.

Thanks - will make it 10 times easier to give some advice to you

/halo - according to ElsoKwak halojoy is "A Fan of John Curl"
- well, not exactly
HKC,
This is probably too much
A way to promote myself, but ....

This is a Thread I started at AudioAsylum:
http://db.audioasylum.com/cgi/m.pl?f...ge&r=&session=

I was "groman" there
Here, I get answers by Thorsten, Elso and John Curl
So I have actually dicussed with JC
not only in this thread - you know I started a lot over at AudioAsylum.
------------------------------

But I am more Happy with this Forum
It has more human qualities, than that doubious AA....

Regards to HKC & Elso

/halo - will have to check his emails
for another JC-construction
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Old 21st January 2003, 08:31 AM   #7
sonnya is offline sonnya  Denmark
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Default Re: Remake of John Curls JC-2

Quote:
Originally posted by Elso Kwak
Hi HKC,
Rather than trying to rebuild a JC-2 may I suggest to build something more "modern" like Sonny Andersons circuit. This easely surpasses the JC-2 in soundquality.

Jfet/bipolar PCB and Schematic (finaly)

Quite a few of the FETs and transistors for the JC-2 are no longer available. Also a monolitic dual sounds much better than a handmatched FET.
If anyone is interrested i am planning to upload a modified circuit with 2N5912 as input diff, BC550B/560B from 2N5401/5551 and J5XX or CRXXX current sources....
place C3 on a starground, which is missing of the old circuit which is really good... but ...

This should eliminate most of the trimmers.....

Should then be able to perform more than 100V/us, and have low distortion and be a "single" gain stage...

any comments?

Sonny
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Old 21st January 2003, 08:39 AM   #8
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Default Re: Re: Remake of John Curls JC-2

Quote:
Originally posted by sonnya


If anyone is interrested i am planning to upload a modified circuit with 2N5912 as input diff, BC550B/560B from 2N5401/5551 and J5XX or CRXXX current sources....

Sonny
Hi Sonny,
I am interested!
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Old 21st January 2003, 08:55 AM   #9
halojoy is offline halojoy  Sweden
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Default So will many other be -including halojoy

Come on, sonnya!
Start a Thread
Can become a lively thread.

--------------------------------
I am in thoughts of buying myself
100+100 2N5401/5551 for use in high voltage applications.
I use 550C/560C so far upto 45v
Thinking of buying
SC2240/SA970 to use for input devices, goes upto 120V
And some BC640/630 maybe

And MJE15030/31 for output/powerdriving.
With MJ15024/25 for high power.

I am quite limited to these choices, as we have almost
only one supplier in Sweden
www.elfa.se - without them, we were lost ...

/halo - likes to increase the voltage in designs
- get more Tube-like
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Old 21st January 2003, 09:40 AM   #10
HKC is offline HKC  Hong Kong
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Default Need to build JC2 preamp

Hello Elso & Halojoy

Thank you for the information for JC2. The Sonny Andersons circuit also interested me. I will make a decision to choose one among the two circuits.
Thanks again for all the inform.
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