"Inverted" Aleph J?

[joe]

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.

 

[Nelson Pass]

Just reverse the polarity of everything, there you have it.

😎

edit - input and output terminals remain the same +/-

 

[Zen Mod]

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

 

[Nelson Pass]

Pa was faster , as usual

I like to cruise by and pick the low hanging fruit.

😎

 

[juma]

...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:
http://www.diyaudio.com/forums/pass-labs/152379-mini-aleph-using-bf862-possible-2.html#post1949735

 

[joe]

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

 

[Zen Mod]

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

 

[njepitt]

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

 

[6L6]

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...

 

[ANADIGIT]

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.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[dieringe]

I really would have liked to see those images ... 🙁

 

[xrk971]

Here is the amp you look for and the thread you want to read:
http://www.diyaudio.com/forums/pass-labs/152379-mini-aleph-using-bf862-possible-2.html#post1949735

Very nice, thanks for the design. Indeed, I have lots of BF862 and IRFP9240 is easy to find.

 

[Zen Mod]

"s" at Q2 and Q5 ?

 

[xrk971]

BF862 is interchangeable S & D

This would be a real cute teeny-tiny inverted micro-Aleph J HPA in an all SMT job with ZVP4525G outputs and SOT23 BJTs. Could probably replace Q4 with BSP129 in SOT223 package to get better heat sinking, Q1 could be SOT223 DZT5401, also for more heat sinking and higher dissipation.

 

[kinku]

How many watts at 8ohm load and how much dissipation per channel?

 

[xrk971]

I didn’t not run a sim or anything but from Juna’s Schematic: +/-18v rails gives 36v max swing, minus 2x4v drop for each mosfet. So 28vpp output which is good for about 12w into 8ohms. Assuming a bias current of say 1.2amps typical of FW amps, that’s 36vx1.2amp=43w dissipation.

 

[juma]

Xrk,
take care about polarities - bottom PSU rail is in this schematic positive

 

[Zen Mod]

BF862 is interchangeable S & D.........

....... wrong answer .... 🙂

however , you cheated - edited post later (new schm) , without trace

 

[Zen Mod]

........ Assuming a bias current of say 1.2amps typical of FW amps, .........

not exactly always ...... and also not exactly figure carved in stone by Papa

 

[xrk971]

....... wrong answer .... 🙂

however , you cheated - edited post later (new schm) , without trace

I saw your question after I updated the schematic as I got to the later post where Juma corrected it.

The manufacturer’s spec sheet says it’s interchangeable. I have built circuits thus and that appears to be a true statement. Why is that the wrong answer?

https://www.nxp.com/docs/en/data-sheet/BF862.pdf