Help wanted: Jfet front-end for Aleph 2 - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 5th March 2014, 07:44 PM   #11
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
sorry - I wasn't clear enough

you must make them as one
, exactly as I drew earlier

like you drew (2 resistors ) , input stage is loosing LTP function ......... big nono

so , either as one resistor , or without it , then having some more dissipation in CCS above
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
  Reply With Quote
Old 5th March 2014, 07:46 PM   #12
diyAudio Member
 
Join Date: Jun 2013
Location: Santiago
Quote:
Originally Posted by wayne View Post
Yes the left one but stick some resistors in the base leg of cascodes 220 Ohms - 1K.
Thanks for the tip, as I could understand I will make a new schema with a pair of resistors in between the base legs of Q75 & Q76.

What value should I use for those resistors? 220Ω - 1KΩ is a wide range.


Regards,
Alejandro
  Reply With Quote
Old 5th March 2014, 07:54 PM   #13
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
anything between 220R to 1K

they're base stoppers , so not critical value
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
  Reply With Quote
Old 5th March 2014, 09:05 PM   #14
diyAudio Member
 
Join Date: Jun 2013
Location: Santiago
Default New Schema

New schema with modifications suggested, R72 was dropped and added R78 & R79, the 390Ω value is just because I have some qty of them.

Also I want to ask for capacitor type recomended for C71 (10µF).


Thanks again.
Alejandro
Attached Images
File Type: jpg A2-Jfet-A_v2.jpg (70.5 KB, 292 views)
  Reply With Quote
Old 5th March 2014, 09:50 PM   #15
gl is offline gl  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Sierra Foothills - California
I would strongly recommend matching all the JFETs in each channel as closely as possible.

I only used the 15 ohm source degeneration resistors in the AX100J because that was the value I had on hand. I also tried no resistors and that worked fine too - but the JFETs were all tightly matched.

I think your Aleph 2J is going to sound really, really nice!

Graeme
  Reply With Quote
Old 5th March 2014, 09:55 PM   #16
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
C71 - 10uF/25V electrolytic is fine
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
  Reply With Quote
Old 6th March 2014, 12:47 AM   #17
moe29 is offline moe29  United States
diyAudio Member
 
moe29's Avatar
 
Join Date: Dec 2002
Location: Florida
Send a message via AIM to moe29 Send a message via Yahoo to moe29
I would love to try this - i've just been looking at my long dormant Aleph 2s, to re-do the wiring and fix a few things.

A chance to refresh them with a new front end would really rock!

I wish i could do more than just offer moral support, but it's over my head technically
  Reply With Quote
Old 6th March 2014, 01:38 AM   #18
diyAudio Member
 
Join Date: Jun 2013
Location: Santiago
Quote:
Originally Posted by gl View Post
I would strongly recommend matching all the JFETs in each channel as closely as possible.

I only used the 15 ohm source degeneration resistors in the AX100J because that was the value I had on hand. I also tried no resistors and that worked fine too - but the JFETs were all tightly matched.

I think your Aleph 2J is going to sound really, really nice!

Graeme
Thank you for your advice, fortunately today is still possible to buy the Toshiba 2SJ74BL in matched quads. I have some LSJ74 but I haven't luck with match, I will need to continue buying more units to get a good matched subset.

Best regards,
Alejandro
  Reply With Quote
Old 6th March 2014, 01:44 AM   #19
diyAudio Member
 
Join Date: Jun 2013
Location: Santiago
Quote:
Originally Posted by Zen Mod View Post
C71 - 10uF/25V electrolytic is fine
OK thanks, I need to change the symbol in the schema, I was thinking in a non polarized capacitor.


Thanks,
Alejandro
  Reply With Quote
Old 6th March 2014, 09:40 PM   #20
diyAudio Member
 
Join Date: Jun 2013
Location: Santiago
Default Daughterboard design finished

I have finished the Aleph 2 Jfet daughterboard design (I hope ), there are 4 attached images, from left to right, (1) original Aleph 2 input stage, (2) the revised Aleph 2 Jfet input stage, (3) the actual mainboard IRF9610 diff pair and (4) the Jfet daughterboard PCB.

J1 & J2 are the connections from daughterboard to Q1 & Q2 (IRF9610s) on the main Aleph 2 board respectively, the orientation of pins is exactly as they are on the mainboard. Also the distance between Q1 & Q2 is the same as in between J1 & J2 (30mm or 1.18in), the idea is to directly plug the daughterboard into Q1 & Q2 pin connections.

An important fact is that drain pin of Q2 (center pin) is directly connected to negative rail, another fact is “source” pin of both Q1 & Q2 are already direct connected at the mainboard level as the original design states, as a way of simplify daughterboard design only the “source” pin of Q2 was used.

The rest is in the previous posts.

I have changed some resistors designations in the schema because there was a repeated number.

If anyone has time to see the diagrams and the PCB, and post any comment I will be very gratefully.


Thanks in advance.
Alejandro
Attached Images
File Type: jpg A2-IRF9610-Orig-Design.jpg (57.1 KB, 245 views)
File Type: jpg A2-Jfet-A_v3.jpg (70.3 KB, 246 views)
File Type: jpg A2-IRF9610-Diff-Pair.jpg (73.5 KB, 246 views)
File Type: jpg A2-Jfet-Daughterboard.jpg (119.8 KB, 235 views)
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
BD140 I/o 9610 in Aleph type front end? kasey197 Pass Labs 5 24th March 2013 05:47 PM
Aleph J front end as pre amp??? audionut Pass Labs 2 2nd February 2012 05:32 AM
Aleph J Front End for Pre Bengali Pass Labs 5 2nd November 2009 10:51 PM
Can I use the 2N5484 jfet diff pair in an audio amplifier front end? carpenter Pass Labs 27 28th March 2009 01:55 AM
Please help me check the Aleph Front end PCB Layout acliao Pass Labs 5 20th June 2002 08:58 AM


New To Site? Need Help?

All times are GMT. The time now is 07:28 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2