Finally my J2 clone is up and running
After many years of collecting components, I managed to find the time and courage to take the plunge to complete the J2 clone.
When I began, I wasn't sure if clone design would even work. It was a leap of faith and was willing to sacrifice the precious SemiSouths if something went wrong.
Managed to measure the IDSS of J74 and K170s in my stock and got the required matches. I was quite intrigued by the low part count in the design. Read lot of posts and figured out how to measure the current through the SemiSouths and how to use the matched pairs.
I had to dismantle my Aleph J build for the chassis and powersupply. Everything measured and worked like a breeze. Not a glitch or debug. First with cheap speakers and then my Tannoys.
Works beautifully with rich and detailed sound.
Shut the lid and start using. Will reopen if Papa publishes an official circuit.
Thanks to this forum for such a wealth of info, which helped me build the amp.
Cheers
Anil
After many years of collecting components, I managed to find the time and courage to take the plunge to complete the J2 clone.
When I began, I wasn't sure if clone design would even work. It was a leap of faith and was willing to sacrifice the precious SemiSouths if something went wrong.
Managed to measure the IDSS of J74 and K170s in my stock and got the required matches. I was quite intrigued by the low part count in the design. Read lot of posts and figured out how to measure the current through the SemiSouths and how to use the matched pairs.
I had to dismantle my Aleph J build for the chassis and powersupply. Everything measured and worked like a breeze. Not a glitch or debug. First with cheap speakers and then my Tannoys.
Works beautifully with rich and detailed sound.
Shut the lid and start using. Will reopen if Papa publishes an official circuit.
Thanks to this forum for such a wealth of info, which helped me build the amp.
Cheers
Anil
Using the original Toshiba 2SJ74 "Gr" grade jfets on the J2 is fine? I got a bunch of them from eBay seller "punkydawgs" which as per his description are in the range of 3-6mA and I can do some matching quads from them to use on my J2 build instead of the 2SJ109. Or is it required to use only with "Bl" grade jfets in this place?
Thanks
Thanks
If you have some sextets at the upper end (5 or 6mA), just use 3 per side (instead of the 2 normally used).
If you use lower, you'll want to adjust the CCS accordingly so that you don't feed them too much current.
Those are my best guesses. Hopefully someone else will be along with another opinion....
If you use lower, you'll want to adjust the CCS accordingly so that you don't feed them too much current.
Those are my best guesses. Hopefully someone else will be along with another opinion....
Thanks, I have one on way from you, and one from him. Thanks to both of you.
Russellc
Thanks Jeff, I did not want to take the risk or doubt
So cancelled the 20 unmatched Gr grade and went ahead and ordered the Octet set of 2SJ74Bl grade within 8-10mA IDSS from punkydwags. Quite expensive but the amp deserves it I guess.
From what I read from various comments including papa’s there are 2 pairs of 2SJ74s. Within the pair there needs to be match. Minimum idss of each jFet should be 6mA. Across the pairs you don’t need to match. It doesn’t matter whether it is Gr or BL types.
Cheers
Anil
