Go Back   Home > Forums > >

Pass Labs This forum is dedicated to Pass Labs discussion.

Beast with 1000 JFETs redux ?
Beast with 1000 JFETs redux ?
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
Old 20th January 2021, 06:32 PM   #171
vitorio is offline vitorio  Spain
diyAudio Member
 
Join Date: May 2010
Location: Grao de Castellón / Madrid
Woofertester, thank you for so long and detailed answer. Many things are clearer now.

I have to: classify jfets, check wattage/dissipation, put bigger resistors, change pinouts, make some boards and mount two amps.

I think it worths trying, even it's at my limit. We're confinated now in Spain, boredom is my friend.
Again thank you
__________________
B1 preamp + M2 clone amp
  Reply With Quote
Old 21st January 2021, 12:53 AM   #172
woofertester is offline woofertester  United States
diyAudio Member
 
Join Date: Jun 2011
Quote:
Originally Posted by vitorio View Post
Woofertester, thank you for so long and detailed answer. Many things are clearer now.

I have to: classify jfets, check wattage/dissipation, put bigger resistors, change pinouts, make some boards and mount two amps.

I think it worths trying, even it's at my limit. We're confinated now in Spain, boredom is my friend.
Again thank you
I hope this helps relieve some boredom for you.
  Reply With Quote
Old 21st January 2021, 11:32 AM   #173
woofertester is offline woofertester  United States
diyAudio Member
 
Join Date: Jun 2011
Quote:
Originally Posted by vitorio View Post
Woofertester, thank you for so long and detailed answer. Many things are clearer now.

I have to: classify jfets, check wattage/dissipation, put bigger resistors, change pinouts, make some boards and mount two amps.

I think it worths trying, even it's at my limit. We're confinated now in Spain, boredom is my friend.
Again thank you
Bigger resistors will not solve a power dissipation problem. The circuit will have to be redesigned to add source resistors for local degeneration. This will lower bias current and may increase output resistance.

For now, just live with the J175 operating its power limit.
  Reply With Quote
Old 21st January 2021, 06:33 PM   #174
Kris0603 is offline Kris0603  Sweden
diyAudio Member
 
Join Date: Jul 2004
Location: Sthlm
I wonder if anyone considered putting their beasts in a tank and filling it up with fluorinert and an aquarium pump to circulate, one of those neat waterfalls for cooling just like Cray did.
  Reply With Quote
Old 21st January 2021, 06:36 PM   #175
Zen Mod is offline Zen Mod  Serbia
Official Court Jester
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
Beast with 1000 JFETs redux ?
HAM Geezers did that with their melting 807s and 6L6 ..... bucket of oil ......

why one should the same with eeny tiny weeny JFets?

if you push them in enormous current region , byebye any linearity
__________________
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 21st January 2021, 06:50 PM   #176
woofertester is offline woofertester  United States
diyAudio Member
 
Join Date: Jun 2011
Quote:
Originally Posted by Zen Mod View Post

if you push them in enormous current region , byebye any linearity
When I have a pcb populated, I will post some scope shots. If linearity is bad, it should be visible on the scope.
  Reply With Quote
Old 21st January 2021, 07:09 PM   #177
Zen Mod is offline Zen Mod  Serbia
Official Court Jester
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
Beast with 1000 JFETs redux ?
enormous current region means - above Idss ....... gate going positive ref. to source

I can't see that your pcbs are made to accommodate that (and they shouldn't be)
__________________
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 21st January 2021, 07:48 PM   #178
Biosonar is offline Biosonar  United States
diyAudio Member
 
Join Date: May 2005
Location: Pennsylvania
Below is the basic schematic for a CCS beast cell. R3 is just a gate resistor. Any value from 200 to 1k ohms will fine. Nelson's micro-beast uses 470 ohms for R3.

For good linearity from the J113 jfet, Nelson's bias resistor, R2, is 47 ohms for 10 to 15 milliwatts dissipation per J113. Even at that dissipation, I can't keep my fingers on the jfets for more that 10 seconds. So heat dissipation needs to be taken into account.

Lastly, R1 is 47 ohms. One drawback of the J113 jfet is Idss values range from 7 to 30. So matching J113s is important.
  Reply With Quote
Old 21st January 2021, 07:50 PM   #179
Biosonar is offline Biosonar  United States
diyAudio Member
 
Join Date: May 2005
Location: Pennsylvania
The CCS micro-beast schematic:
Attached Images
File Type: jpeg C459222A-8B35-4ED7-890F-0C9C14906961.jpeg (82.5 KB, 201 views)
  Reply With Quote
Old 21st January 2021, 08:29 PM   #180
wattsman is offline wattsman  United States
diyAudio Member
 
Join Date: Sep 2016
Location: Jackson, Mississippi 39212
Thank you!for the schematic and the information.

Best regards, Frank
  Reply With Quote

Reply


Beast with 1000 JFETs redux ?Hide this!Advertise here!
Thread Tools

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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
tube x-over noise redux jlg4104 Tubes / Valves 4 12th December 2020 01:31 AM
Article: Beast With a Thousand Jfets Nelson Pass Pass Labs 126 18th September 2019 09:35 PM
The Beast with a Dozen Jfets wrenchone Pass Labs 30 24th June 2013 04:31 AM
Beast with a Thousand JFETs Nelson Pass Pass Labs 297 18th May 2013 12:38 PM
Guidelines for switching N-channel JFETs to P-channel JFETs (and vica versa)? Test Electrix Construction Tips 9 24th January 2011 07:22 PM


New To Site? Need Help?

All times are GMT. The time now is 08:43 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio
Wiki