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Old 27th September 2013, 01:43 PM   #1
joe is offline joe  Germany
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Default "Inverted" Aleph J?

Hi,
Inspite of the fact that the LSJ74 is temporarily available, isn't it possible to "mirror" the aleph J and replace n-channel with p-channel and vice a versa. This way one could use the sk170 (or even sk389) for the front end which are still easier to get. Also the ciss/crss for sk170 are lower which I have been told is a good thing for low distortion.

Is this possible to redesign it in the inverted way or do I miss something?

Thx
Joe

p.s. As I already have the diystore boards and got my hands on two SJ75 (which is 2 times sj74 glued together in a metal housing) I will probably build it as is, so this is more a educational question.

Last edited by joe; 27th September 2013 at 01:47 PM.
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Old 27th September 2013, 02:34 PM   #2
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Just reverse the polarity of everything, there you have it.



edit - input and output terminals remain the same +/-
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Old 27th September 2013, 02:35 PM   #3
Zen Mod is offline Zen Mod  Serbia
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possible and already made , even if I can't remember where I read about it .

however - FE Jfets , being biased through CCS , are much easier to change for something less troublesome to have/find

J271 , for instance

edit: Pa was faster , as usual
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Old 27th September 2013, 04:05 PM   #4
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Quote:
Originally Posted by Zen Mod View Post
Pa was faster , as usual
I like to cruise by and pick the low hanging fruit.

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Old 27th September 2013, 04:17 PM   #5
juma is online now juma  Serbia
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Quote:
Originally Posted by joe View Post
...isn't it possible to "mirror" the aleph J and replace n-channel with p-channel and vice a versa....
Here is the amp you look for and the thread you want to read:
Is a mini-Aleph using BF862 possible?
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Old 27th September 2013, 04:44 PM   #6
joe is offline joe  Germany
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Thx guys. Good link.

Could not find a jfet called (2s?)j271. Is the spelling corect?

Btw, do you have experience with sj75? I measured idss of the halfes and they are 10% different which I find disappointing.
Still need to messure the pinch off voltage to ensure the parts are genuine.

Joe
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Old 27th September 2013, 04:50 PM   #7
Zen Mod is offline Zen Mod  Serbia
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if they're 2SJ75 , just go with them

Juma pointed you where to read rest of the story

not 2s in front of J271

http://www.fairchildsemi.com/ds/J2/J271.pdf
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Old 30th September 2013, 01:16 AM   #8
njepitt is offline njepitt  United Kingdom
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Hi,

If anyone else is considering an "inverted" Aleph J, the amp I built following juma's schematic (in the thread he linked to) sounded very good. I haven't used it for a while (for various reasons I've been listening to music on my diy DAO headphone amp) but I intend to rebuild it in a new and (hopefully) improved version as soon as I can. (I have Toshiba output devices I got from buzzforb... The delay is due to a recent move to the USA, meaning all my diy stuff is in packing crates...)

I'd be interested to hear from anyone else who has tried an "inverted" Aleph J...

Nigel
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Old 30th September 2013, 11:55 AM   #9
6L6 is offline 6L6  United States
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If you are wanting to invert the amp as an engineering exercise, that's wonderful! Have fun!

If you are just wanting to build an Aleph J, member ' spencer ' and member ' h_a ' have plenty of genuine Toshiba J74...
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Old 1st October 2013, 12:38 PM   #10
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Hi, JOE
You have a same idea with me, too
I used 2SK389BL idss 10mA instead of 2SJ109BL and also inverted polarity all of amp function.

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