Variation on the JC-2 preamplifier

[HKC]

Hi Mr. Curl

Thank you for your advice. I have ordered some 10p & 20p silver mica caps from RS which should be delivered next week. C2 is a 4.7uF capacitor. I could not found this value in RS's silver mica list so I use tan cap instead.

 

[john curl]

If it is an electrolytic, it is probably OK. I worry about ceramic caps, mostly.

 

[HKC]

JC-2 clone new up dates:

 

[HKC]

One more picture:

 

[micio_mao]

Hi,
I bought the tubeshunter kit for JC2, I assembled it but it can't work..
Anybody of you could attach me a photo of the corrected jfet positions?! I think the silk screen wasn't correct....

Thank you!
Matteo

 

[jonusgrumby]

The input fet orientation is OK. The bipolar transistors supplied with the kit I ordered (Q5 and Q6) were shown with their pin outs reversed on the silk screen. You may need to test your Q5 and Q6 devices to see if they are installed according to their actual pin out.

Good luck.

 

[micio_mao]

Hi Tom,
thank you for your suggestion, I checked the output transistors and they are ok, I check the pins and the layout with their datasheets.

I have a doubt about imput jfet because in the photo here http://i220.photobucket.com/albums/dd220/tubeshunter/jcamp1.jpg they seems to be soldered in different position about silk screen...
In the silk screen they are in front but in the photo they are opposite...

Matteo

 

[micio_mao]

Hi everybody,
I can't find the right way!
I turned the jfets as in photo but it isn't a solution,
the situation is the same... I measure 125 mA in V+ and 125 mA in V-, so the supply limited the current and there's something wrong in JC2...

How can I do?!

Matteo

 

[micio_mao]

Hi everybody!

I found the solution!!!
As Tom told me the output transistor are in wrong position in the silk screen, they only be turned round 180°!!!!!

It works and now I listen some nice music!!!

Matteo

 

[PB2]

The parts that I found best were made by RCA and Kertron, both difficult parts to get today. I would recommend a plastic equivalent part pair, today, 40V min breakdown, good Ft, linear beta between 5 and 50ma, power diss. 0.5W min, 2W if you can get it. As I don't use bipolar transistors very often, anymore, I don't have a good recommendation at the moment

JC might those RCAs have been the 40409/40410 with the integral heat sink?

Pete B.

 

[MikeBettinger]

JC might those RCAs have been the 40409/40410 with the integral heat sink?

Pete B.

I remember these as the driver transistors in the HK Citation 12 amp. My first real power amp... Differential input and dual mono power supplies. Copied right out of the RCA application notes. Still have it somewhere.

 

[whaleman]

Sorry to revive this old thread from the dead, but I just bought another JC-2 preamp kit from Hong Kong, hopefully as good as the tubehunter's and not too hacked from Mr. Curl's original intention.

JC-2 Preamp kit from eBay seller jims_audio here

I have this lonely Parasound HCA-800II that just needs a mate.

 

[jonusgrumby]

Should be a fun project for the winter. I'd replace the pots with fixed resistors once you get the circuit working.

 

[whaleman]

Finished the pre over the weekend. It is great! Started out a tab bright and then settled into a very nice laid back disposition.

Actually loved all those pots and being able to fine tune things. The seller (Jim'saudio) uses other transistors other the KFET/JFET and bias is run higher at 2.5 - 3 volts.

Here is a breadboard pic. Case and other parts are being readied.

 

[whaleman]

This is the home I am building the JC-2. May need you all's help coupling those stages properly.

That is an Audio Sector three tone board, Audiowind OPA2134 based phono pre and Rubycon cap loaded power conditioning board.

 

[AHaa]

Nice project, whaleman! Keep us updated as your project continues.

I'm starting my first diy hifi project soon because I need a preamp for my active monitors. I'm going to use the same kit for preamp as you and include DAC and remote controlling. Maybe I'll include also the tone control kit. How are you going to make the input selection? Where did you buy the transformer and chassis?

 

[whaleman]

Nice project, whaleman! Keep us updated as your project continues.

I'm starting my first diy hifi project soon because I need a preamp for my active monitors. I'm going to use the same kit for preamp as you and include DAC and remote controlling. Maybe I'll include also the tone control kit. How are you going to make the input selection? Where did you buy the transformer and chassis?

Be glad to update.

The project is done for all practical purpose. The JC-2 preamp has met and surpassed all expectation. This is the first preamp that I turned on and after a couple of hours burn-in, I really had to tell myself that I was not listening to a several thousand dollar preamp. It lacks nothing!

The tone board is totally unnecessary and adds nothing for line level use--and I got the wrong pots with it, so in the middle of already drilling holes for it, I had to scrap its use. It may be useful for the phono amp.

I highly recommend the JC-2 kit from eBay seller jims_audio. He is very helpful with questions and seems on top of his audio knowledge and aim.

I will post the part numbers for those interested.

Thanks Mr. Curl for sharing this awesome proven design!

More pictures here: JC-2 Preamp

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

 

[DarthBubba]

Could somebody attach/upload the most recent version schematics of the John Curl phono and pre (line) amps? Any updates added due to parts improvements or substitutions due to manufacturer cessation would be appreciated. If they're the ones attached to the earliest messages, then please let me know.

Nice looking work, Whaleman!

 

[carlmart]

Finished the pre over the weekend. It is great! Started out a tab bright and then settled into a very nice laid back disposition.

Actually loved all those pots and being able to fine tune things. The seller (Jim'saudio) uses other transistors other the KFET/JFET and bias is run higher at 2.5 - 3 volts.

Here is a breadboard pic. Case and other parts are being readied.

Do you have the schematic?

I was interested in the kit, but Jim's Audio refused to provide one. I never buy any eBay clone without having a look at what I'm buying.

What pot did you use and where did you get it?

AFAIK the pot is not in the kit, right?

What regulated supply did you use?

 

[gk7]

Here you can find a thread about building the original JC-2 circuit with modern parts:
http://www.diyaudio.com/forums/solid-state/10160-need-build-jc-2-preamp-19.html

The final schematic in post #188 is what I use in my ML-1 for almost two years now.