Hey keilau,
Thanks for the link. That confirms that the board I have is identical to the one offered an eBay. I was just wondering if there was a more 'official' version of John Curl's JC-2.
These are the official JC-2 versions.
Mark Levinson Vintage Audio Gear: JC-2 | Preamplifier | 1974 - 1977
Mark Levinson Vintage Audio Gear: JC-2 | Preamplifier | 1974 - 1977
For what it's worth, i built the Jc2 from Jim's Audio. Bought the pcbs only, and used my own components. Quite frankly wonderful preamp for the dough. The sound startles me sometimes, hooked to a 55w ab amp.
If you go back to the 2016 period of this thread, John Curl made many comments himself. From what John said, the 'official' version is on how the input FET's are selected. John gave enough detail on how a DIYer can do it. But getting enough spare devices for the selection can be quite expensive.
The JC2 offers on e-bay are mostly output stage only, not the phono stage. I purchased one out of curiosity. It sound ok, but not exceptional. I tried a clone of the SUGDEN SDA-1 DAC output stage. I replaced the NE55834 with LME49710 from US supplier. It sound much better than the un-optimized JC-2 output stage.
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The input devices are not genuine dual low noise 2SK146. It uses 4 uPA68HA for all dual junction FET. Hopefully, they are matched well. The slightly high noise may be acceptable for line stage.
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JC-2
Hello.
Guys please help me to adjust the preamp named merk levinson JC-2
There are two variable resistor in preamp section 1k both.
If somebody have the instruction or manual i will appreciate so see it.
Hello.
Guys please help me to adjust the preamp named merk levinson JC-2
There are two variable resistor in preamp section 1k both.
If somebody have the instruction or manual i will appreciate so see it.
![IMG_20200102_173925[1].jpg](/community/data/attachments/741/741355-1edeb79405f6d74662e7bab9cd1af967.jpg?hash=Ht63lAX210)
The e-bay seller does not want to give user schematics or only bogus one. Your schematic has no trim pot.
The actual Mark Levinson JC2 line preamp do have a pair of trim pot. One for input FET bias and one for output DC offset.
Check the output offset before the C10 output coupling cap. If there is no excessive DC offset voltage, left everything alone and just use the preamp. If the DC volt is high (>0.1V), call Breeze Audio for help. You can see that your preamp is quite different from the Mark Levinson JC2. The 1Kohm variable resistors are nowhere near the JC2 value.
Can't upload image here.
An externally hosted image should be here but it was not working when we last tested it.
R5 zero point adjusting.
1k above R4 adjust quiescent current.
I started from 30mv on R10 J1 and J2 points and finished on 150mv. The output transistors tempoerature is about 40 degrees. Sounds is good.
First adjust the quiescent current, next zero point. The schematics above is 100% matched this board, so hope it will be usefull for someone.
This was more between 1991 and 1993 as I was there too. Rhapsody, Hilversum Netherlands
🙂
Where do you get mated jfets for the input? The four of them I mean.
The other transistors are obsolete too, unavailable.
How about building a JC2 with all components you can arrange now, particularly the fets?
You can get them for much cheaper price at the DIYAUDIO Store right here.
Linear Systems Matched JFETs – diyAudio Store