Well, I hope the original schematics keep you guys on the right track. The JC-80 was a relatively successful design for its time (25-30 years ago), but the phono stage was soon superseded by the Vendetta designs. Big time people, looking for the 'best sound possible' like Dave Wilson and many audio reviewers, bought them. The 'core' of this design is still visible in many of today's highest quality preamps, including the Parasound JC-2 and the Constellation Audio series.
It is NOT important to 'slavishly' follow each and every circuit value or part in your own versions, but try not to deviate TOO MUCH from the ESSENCE of this design.
It is 4 quadrant symmetry, all fet, medium feedback, Class A, with reasonably high open loop bandwidth. It is NOT an OP AMP.
The power supplies can be modified (improved). I recommend a floating ground, rather than a CT ground. However you CAN add a air coil choke (think loudspeaker Xover choke) in series with the CT to keep the garbage from the CT into the preamp ground.
Shunt regulators are OK, as well. Good luck!
It is NOT important to 'slavishly' follow each and every circuit value or part in your own versions, but try not to deviate TOO MUCH from the ESSENCE of this design.
It is 4 quadrant symmetry, all fet, medium feedback, Class A, with reasonably high open loop bandwidth. It is NOT an OP AMP.
The power supplies can be modified (improved). I recommend a floating ground, rather than a CT ground. However you CAN add a air coil choke (think loudspeaker Xover choke) in series with the CT to keep the garbage from the CT into the preamp ground.
Shunt regulators are OK, as well. Good luck!
Hi,
Where does one obtain a kit to build this?
Does the JC-2 resemble the JC-80 in anyway? I've found this: Symmetric Complementary J-FET preamplifier JC-2 kit ! | eBay
Kind regards,
Chris
Where does one obtain a kit to build this?
Does the JC-2 resemble the JC-80 in anyway? I've found this: Symmetric Complementary J-FET preamplifier JC-2 kit ! | eBay
Kind regards,
Chris
I am just trying to repair my own Dennesen JC-80, the line stage section is working and is very, very good. The phono has no output and I suspect a bad FET, at least that's where the signal stops and the FETs have had their model numbers removed. It's a beautiful preamp even with it's "obsolete" phono section.
Thank you,
John
Thank you,
John
Hi John,
Would you be able to give me a hint on the value of the air coil to be put in series with CT?
Thanks
Do
Hi JKoch,
I'm currently using two Sigma 22 for the JC-80 and they're better than the Borbely I had.
Have fun with the build!
Do
Hi pinnocchio
Mainly I based on your listening test about sigma22 vs. Borbely, so I decide to build the sigma22. But it will be pcb dedicated to my project (different/better components, different dimensions, custom-made heat-sinks). I will publish the pcb design after finish.
In Ist stage of my psu I used 3 el-caps as was mentioned in this thread: 2x full-wave bridges (connected together, not grounded), 1x el-cap connected to +/- rails (not grounded), common choke (how mH?), resistors in each rail, 2x el-caps in each rail connected to common ground. Next stages: sigma22 + cap multiplayer + JC-80.
I found 2SK216/2SJ79 on 2SK216 2SJ79 K216 J79 Transistors One Pair on sale - electronic parts and components supply store but I do not sure they are genuine Hitachi. maybe someone have any opinion about the seller?
Mainly I based on your listening test about sigma22 vs. Borbely, so I decide to build the sigma22. But it will be pcb dedicated to my project (different/better components, different dimensions, custom-made heat-sinks). I will publish the pcb design after finish.
In Ist stage of my psu I used 3 el-caps as was mentioned in this thread: 2x full-wave bridges (connected together, not grounded), 1x el-cap connected to +/- rails (not grounded), common choke (how mH?), resistors in each rail, 2x el-caps in each rail connected to common ground. Next stages: sigma22 + cap multiplayer + JC-80.
I found 2SK216/2SJ79 on 2SK216 2SJ79 K216 J79 Transistors One Pair on sale - electronic parts and components supply store but I do not sure they are genuine Hitachi. maybe someone have any opinion about the seller?
Hi JKoch,
On the component quality side of my build I'm using premium components such as Vishay Z-Foil TX-2575, Caddock Film TF-020 and Dale resistors as well as good quality CAPs such as ClarityCAP MR, Nichicon KZ. Unfortunately on the transistor side I'm using IRF 610/9610. Had a pair of used pulls (genuine) 2SK216/79 but the legs were pure copper and broke right at the end when just aligning the pins...
You won't find any new 2SK216/79 on the market. Those will most likely be all fakes. Try and find some used pulls.
For the inductor, as Ticknpop said if you are using dual full wuve bridges you can do without them.
Ciao!
Do
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