O.H. Schade(1938) meets MOSFET - Page 4 - 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 7th November 2012, 06:10 PM   #31
diyAudio Member
 
Join Date: Jan 2012
Location: Pennsylvania
Blog Entries: 1
Quote:
Originally Posted by avincenty View Post
A BJT

The JFET curves look more like a real triode. The BJT looks extremely linear though.
Thank you avincenty for your interesting results. Did you convert a run of the mill bjt to a new and linear solid state triode? What is the relevance of "extremely linear" in application? I hope it is good if it sounds triodish?
  Reply With Quote
Old 7th November 2012, 06:26 PM   #32
diyAudio Member
 
Join Date: Jan 2008
Location: Southern California
Yes, a 2N3904.

Not sure about how it would sound. I am not really a solid state person, more into tubes, but I'd think that it would have much less distortion and won't have a tube sound.

I think the JFET will have more even harmonics like a triode and would sound more toobie.
  Reply With Quote
Old 7th November 2012, 06:33 PM   #33
diyAudio Member
 
Join Date: Jan 2012
Location: Pennsylvania
Blog Entries: 1
Quote:
Originally Posted by avincenty View Post
Just for fun, I traced some curves for the NTE451 JFET that show the effect of parallel feedback. It indeed works as advertized (on the curve tracer).



Link to video of curves using a potentiometer to vary the amount of feedback
Thanks avincenty for the interesting video. Creative, instructional and showed that one gets a tweakble solid state triode performance! Was feedback from drain to gate increasing as a function of time? Do you have another video like it for bjt to understand its behavior?. Best regards.
  Reply With Quote
Old 7th November 2012, 07:42 PM   #34
diyAudio Member
 
Join Date: Jan 2008
Location: Southern California
I did not video the BJT but the behavior is the same. The more feedback the more vertical the curves get.
  Reply With Quote
Old 7th November 2012, 07:49 PM   #35
diyAudio Member
 
Join Date: Jan 2012
Location: Pennsylvania
Blog Entries: 1
Quote:
Originally Posted by avincenty View Post
I did not video the BJT but the behavior is the same. The more feedback the more vertical the curves get.
Thank you avincenty.
  Reply With Quote
Old 7th November 2012, 08:46 PM   #36
diyAudio Member
 
Join Date: Jan 2012
Location: Pennsylvania
Blog Entries: 1
Quote:
Originally Posted by Antoinel View Post
Thank you avincenty.
avincenty: Schade feedback concerns itself with a current source amp; also called a transconductance amp [TCA]. Please take a look at the F1 schematic in its service manual at www.firstwatt.com. It is a differential TCA. Mr. Pass used feedback from the drain to the gate of each of the two amplifying MOSFETs. Clearly Schade feedback [inadvertent or not]; which may have sweetened the performance of this amplifier in favor of a triodish sound. Best regards.
  Reply With Quote
Old 7th November 2012, 08:52 PM   #37
diyAudio Member
 
Join Date: May 2001
Blog Entries: 5
Looks more like voltage divider bias to me. (F1)
  Reply With Quote
Old 7th November 2012, 11:55 PM   #38
diyAudio Member
 
Join Date: Jan 2012
Location: Pennsylvania
Blog Entries: 1
Quote:
Originally Posted by Michael Rothacher View Post
Looks more like voltage divider bias to me. (F1)




It is a voltage divider bias. Please note that it also has the signature of Schade feedback of at least the following 3 requirements:
  • MOSFET Q1 [for example] is a current source amplifier.
  • The Gate of Q1 is a summing junction of 2 signals which are out of phase.
  • A feedback resistor is used between the Drain and the Gate of Q1. It generates the out of phase signal which sums with the in-phase input signal at the Gate.
  Reply With Quote
Old 8th November 2012, 12:02 AM   #39
diyAudio Member
 
Join Date: May 2001
Blog Entries: 5
Sounds like you've got it all figured out. I'll just move on.
  Reply With Quote
Old 8th November 2012, 12:45 AM   #40
diyAudio Member
 
Join Date: Jan 2012
Location: Pennsylvania
Blog Entries: 1
Quote:
Originally Posted by Michael Rothacher View Post
Sounds like you've got it all figured out. I'll just move on.
I am a newbee at this fascinating application and learning it . I hope that I am not out of line in my observations. I appreciate your feedback and that of others like wrenchone and Zen Mod. I understand that SIT is a voltage and not a current source amplifier. Thus, it it unclear to me whether Schade Feedback is useful or needed in it to make it behave "more or less triodish" than it already is. Best regards.
  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
What if O.H. Schade had MOSFETs? Michael Koster Tubes / Valves 30 18th January 2011 02:53 PM
Accurian Sender Repair help 15-1938 wirelessrat Solid State 17 4th January 2009 08:24 PM
1938 Caphart Turntable free! KP11520 Everything Else 0 10th August 2008 02:11 AM
Old meets new but can this be solved? barchetta Pass Labs 4 11th March 2007 07:29 PM
Old Meets New philipbarrett Tubes / Valves 3 22nd August 2005 12:03 AM


New To Site? Need Help?

All times are GMT. The time now is 03:09 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