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Old 10th November 2011, 10:37 AM   #11
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Default JC-2

Quote:
Originally Posted by Wolfsin View Post
I never was able to eliminate the DC offset on the first JC-2s and had to resort to blocking caps. That led me to fail to fully appreciate the design. On a later rev I was able to adjust away the offset and get rid of the caps. It sings by comparison!
Are you refering to the kit currently being offered on Ebay by the same dealer who supplied the '80 pcb's?? I've been considering that item for use with a newly built Fetzilla.
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Old 10th November 2011, 12:04 PM   #12
Wolfsin is offline Wolfsin  United States
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Item# 320774357578 is the latest rev of that board. Note that the pot placement is to the right. The prior rev had the pot in the middle but I never built that one, but rather a version around 2009.

As with the earlier rev, I initially did not populate the PS but used an external 18v shunt. Note that I am bridging each can with one JC-2. Out of curiousity I pop'ed the PS but cannot detect the higher noise, perhaps because of its being cancelled at the can.
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Old 11th November 2011, 01:58 AM   #13
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Default Housekeeping

@sandyhooker JC-2(v1.5) is the rev I am so pleased with.

The following link includes a schematic and PCB image of v2 of the JC-80 board I have. The date is one year later. It appears both eBay seller's boards are down-rev.

*????*Dennesen JC-80???????PCB?
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Old 11th November 2011, 03:10 AM   #14
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Default JC-2

Thanks for the corroboration. Interesting that fets were exchanged for bjt's on this latest version. Looks like a good choice for me.

Thanks for the info...
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Old 11th November 2011, 03:40 AM   #15
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You'll find with that with a little bit of surgery you can build the Blowtorch on these boards. I off boarded the servo to use better parts than the surface mount components will allow and the Blowtorch servo needs different connection points than the JC 80. The biggest problem is finding high V grade IDSS 2sj109/2sk389 (or J 74/170 matched pairs) for the Blowtorch rather than the BL grade for the JC 80 - fortunately I stocked up before the great jfet famine and have both matched dual jfets, BlackGates for the cap multipliers, Vishay bulk foil resistors, MIT RTX polystyrenes for the regulator outputs and the servos - this design deserves the best parts.

Last edited by ticknpop; 11th November 2011 at 03:56 AM.
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Old 11th November 2011, 05:12 AM   #16
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Just making the JC-80 line stage would be darn good for just about everybody, except for very hi end. However, there will be problems getting the 'right' mosfets that will work as good as the original ones.
Making a Blowtorch is possible, BUT not for the non-expert.
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Old 11th November 2011, 03:13 PM   #17
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Default Everyman's JC-80

When I read the part about surgery my heart sank. My 'bleeding edge' years are behind me and my goal is to find (or possibly make using J74 / K109 pairs) reasonably priced components and build something better than a JC-2. Keep in mind that I already have great respect for the JC-2. 'nuff said.

I hope to visit the pricey components and question what alternatives exist, e.g. whether 22 0hm Caddocks might substitute for 27 ohms. I would guess that the cost per channel can be kept well under a hundred dollars, and both channels for that price even better. If a vanilla JC-80 would be 'darn good', just think how good a low-cost vanilla JC-80 might be
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Old 11th November 2011, 04:52 PM   #18
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Don't 'cheap out' too much. It is pointless to invest your time, if you are not going to make a sonically 'successful' product. Cheap bypass caps, resistors, etc will only compromise an otherwise 'elegant' design.
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Old 11th November 2011, 05:20 PM   #19
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I will count on you to keep me honest in that regard. The balance between being too cheap and focussing purely on quality is one I have long struggled with. Let me begin with Caddocks -- can I substiture 22 for 27 ohms? These are fairly expensive components, four are required for each channel, so buying a quantity for matching purposes is out of the question. At more than $6 a pop onezy-twozy, they are also a budget buster
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Old 11th November 2011, 05:33 PM   #20
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Should be OK.
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