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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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Old 15th June 2012, 06:36 PM   #161
Just DIY!
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Wow!

Thanks John!!!

You da man!

Do
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Old 15th June 2012, 06:41 PM   #162
Just DIY!
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John,

Would you mind someone making a PCB out of this schematics for DIY only or do you prefer not to?

Thanks
Do
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PREAMPs : AMB α10 + JC-80 clone | Balanced DCB1 | LDR3x | AMPs: AMB β24 | Aleph 5 | VSSA | ML-2 | Fetzilla | Telos 390 Clone | My_Ref FE
DACs : TPA Buffalo II + OPC's NTD1 I/V | TPA OPUS + IVY III Speakers : Jim Holtz Statements | Astasia SD | Tubasson Mark 2
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Old 15th June 2012, 07:30 PM   #163
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These parts (Supertex) have not been made for years in T0-220 packages.
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Old 17th June 2012, 03:22 PM   #164
Wolfsin is offline Wolfsin  United States
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What gift to us all. Thank tou, John.
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Old 17th June 2012, 07:28 PM   #165
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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 The JC-80 was a relatively successful design for its time (25-30 years ago), but the phono stage was soon superseded by the Vendetta designs.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!
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Old 7th July 2012, 03:17 PM   #166
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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
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Old 8th July 2012, 11:04 AM   #167
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Quote:
Originally Posted by undefinedza View Post
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
Nevermind, I've got my answer.
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Old 20th May 2013, 09:59 PM   #168
jsimon is offline jsimon  United States
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Thank you so much for the line amp schematics of the Dennesen JC-80 preamp. Could I also ask for the phono section as well. I know it would be very appreciated by all of us.

Thank you,

John
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Old 21st May 2013, 12:01 AM   #169
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You DON'T want to build the phono. It is obsolete, and difficult to get the parts. Please try something else.
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Old 21st May 2013, 02:01 PM   #170
jsimon is offline jsimon  United States
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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
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