There are two eBay sellers providing balanced mono PCB's inspired by the Dennesen JC-80. They appear to be the same board, I think from hifidiy originally. Has anyone built one of these?
I am trying to assess the cost of aquiring the parts and whether they are even available.
Part two of this thread may be found at
http://www.diyaudio.com/forums/analog-line-level/206797-jc-80-ebay-pcbs-power-train.html
I would like to thank all those who contributed, in the spirit of polite exchange, to this thread. Particularly John Curl. There is much detail here along with many errors and misinterpretations, mostly my own, but a summary of salient points along with a BOM and schematics for a power train may be found early in part 2.
I am trying to assess the cost of aquiring the parts and whether they are even available.
Part two of this thread may be found at
http://www.diyaudio.com/forums/analog-line-level/206797-jc-80-ebay-pcbs-power-train.html
I would like to thank all those who contributed, in the spirit of polite exchange, to this thread. Particularly John Curl. There is much detail here along with many errors and misinterpretations, mostly my own, but a summary of salient points along with a BOM and schematics for a power train may be found early in part 2.
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I must admit to being honored by your taking the time to comment on a copy of your work. It is the line amp section. I have built several JC-2 kits and found the experience very valuable. All have been bridged into headphones and to my ears sound very good.
The PCBs accept dual rails @ 30vDC, but reduce that to 24v and then to 15 volts before it enters the amp and servo sections respectively. That seems wasteful of PCB realestate and energy since I will be building a pair of these and a single 24vDC external supply would seem adequate.
>>If you do not already have sufficient J109/K389 (or better) to match, i wouldn't bother.
This is the other concern. Just how close a match constitutes a match?
The PCBs accept dual rails @ 30vDC, but reduce that to 24v and then to 15 volts before it enters the amp and servo sections respectively. That seems wasteful of PCB realestate and energy since I will be building a pair of these and a single 24vDC external supply would seem adequate.
>>If you do not already have sufficient J109/K389 (or better) to match, i wouldn't bother.
This is the other concern. Just how close a match constitutes a match?
Typo alert: 2SJ389V->2SJ109V above.
V means IDSS of 10-20 (same as C range for LSK389 the "improved second source"). Unfortunately Linear only matches to 10% and it seems likely that any remaining NOS Toshiba parts would have been culls of prior matching efforts.
Since these really are just pairs of SJ74s and SK170s thermally attached, it seems a much easier matching search would be among the singletons. Then comes the issue of thermal attachment. Has "Sponge Bob" succeeded again?
V means IDSS of 10-20 (same as C range for LSK389 the "improved second source"). Unfortunately Linear only matches to 10% and it seems likely that any remaining NOS Toshiba parts would have been culls of prior matching efforts.
Since these really are just pairs of SJ74s and SK170s thermally attached, it seems a much easier matching search would be among the singletons. Then comes the issue of thermal attachment. Has "Sponge Bob" succeeded again?
10% on a bl is a closer match than on a V. In addition, considering the collections of culled singletons remaining from the JC-2 builds where everything was bl, easier too. Thanks.
I must admit the PCB is beautiful. Just enough surface mount to be a challenge (the servo area beneath) surrounded by wide gold traces for the power. 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!
I must admit the PCB is beautiful. Just enough surface mount to be a challenge (the servo area beneath) surrounded by wide gold traces for the power. 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!
JC-2
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.
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.
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.
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.
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?
@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?
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.
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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
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
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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