JC-80 eBay PCBs

[Wolfsin]

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

JC-80 eBay PCBs & Power Train

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.

[jacco vermeulen]

If you do not already have sufficient J109/K389 (or better) to match, i wouldn't bother.

[john curl]

The JC-80 line amp is OK, in fact, very good, but the phono section is complex and not so good.

[Wolfsin]

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?

[john curl]

It requires a good same device match, but the complementary match is more forgiving.

[Wolfsin]

The BOM includes a single instance of each of 2SK389V and 2SJ389V per PCB. Is it reasonable to assume that both transistors within a dual package would be adequately matched?

[Wolfsin]

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?

[john curl]

Blue or BL would be OK for the JC-80.

[Wolfsin]

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!

[john curl]

The JC-80 should have servos, if it is true to the original.