Analysing power requirements (Class-A+C/AB2) - Page 5 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 6th December 2010, 02:28 AM   #41
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
Quote:
Originally Posted by Wavebourn View Post
Triode don't have non-linearities of higher orders that are essential to devices linearized by negative feedback.

How can you explain that, if it's a pentode with internal negative feedback?

Here is an example of what happens when negative feedback is applied to the device with 10% of distortions of 2'nd order only:
feedback from the plate V isn't linear - nonlinear feedback with a nonlinear gain mechanism isn't going to follow the rule for linear feedback around a nonlinear gain

how different does a cascoded triode look from one with high plate V excursion?




but I'd really rather people look at the Black Feedforward sim and tell me if it really works - I threw it together fairly quickly as my 1st attempt to understand "current dumping"

Last edited by jcx; 6th December 2010 at 02:30 AM.
  Reply With Quote
Old 6th December 2010, 09:43 PM   #42
WuYit is offline WuYit  Sweden
Banned
 
Join Date: Oct 2010
jcx,
itīs about controlling electric fields. It must occur in a straightforward and direct manner, time is a crucial factor, otherwise the collateral damage will be huge, like in the case of global feedback.
  Reply With Quote
Old 6th December 2010, 09:57 PM   #43
Account disabled at member's request
 
MJL21193's Avatar
 
Join Date: Mar 2007
Quote:
Originally Posted by WuYit View Post
jcx,
itīs about controlling electric fields. It must occur in a straightforward and direct manner, time is a crucial factor, otherwise the collateral damage will be huge, like in the case of global feedback.
Very Interesting lumba...err sorry, WuYit.


Last edited by MJL21193; 6th December 2010 at 10:02 PM.
  Reply With Quote
Old 6th December 2010, 10:08 PM   #44
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally Posted by jcx View Post

how different does a cascoded triode look from one with high plate V excursion?
Do you mean how different high current swing VS low current swing look?
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 7th December 2010, 12:16 AM   #45
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
how about discussing the thread topic

traversing the ~1.2 V dead zone in the unbiased bjt follower and the sudden gain change as the Class C Qs turn on is hard for negative feedback correct

the Black Feedforward scheme works very well in comparison - or has anybody looked yet?

a little bias still helps lots though - adding just 10mA bias to my sim resulted in sub ppm distortion for 240mA peak load current levels - not too bad




for those still interested in tube theory just try some search: Langmuir-Childs law

Improved vacuum tube models for SPICE, Part 1

basically the Vgc and Vgp voltages control the current via the same nonlinear law

Last edited by jcx; 7th December 2010 at 12:20 AM.
  Reply With Quote
Old 7th December 2010, 08:13 AM   #46
diyAudio Member
 
Join Date: Apr 2010
Location: Coffs Harbour
Quote:
Originally Posted by jcx View Post
the Black Feedforward scheme works very well in comparison - or has anybody looked yet?...................a little bias still helps lots though - adding just 10mA bias to my sim resulted in sub ppm distortion for 240mA peak load current levels - not too bad
Thanks for the investigation, JCX. Whilst "toobs" are just as valid for research, I got the impression that the OP was solid state. Would you care to look at this also from your perspective as your simulation has some interesting results. It seems it may also give an alternative direction to the current wave of EC interest.
__________________
regards
  Reply With Quote
Old 7th December 2010, 11:08 AM   #47
mt490 is offline mt490  Australia
diyAudio Member
 
Join Date: Jun 2010
I had a look at Black's feedforward but I would probably implement the floating load realisation rather than the paralleled output system. The main thing in my mind is to look at the performance when playing back low level signals as well, which means that as jcx you noticed that minimising inherent system errors is still a better method than just compensating for them.

As for my design in the OP, I really haven't done much to it aside from put a diode connected transistors between the inner outputs to reduce the biasing variation due to variations of the main biasing transistor.

I've transferred it to LTSpice to gain some better insight into usage with MOSFET's with this arrangement, unfortunately I'm still having issues with getting the various subcircuit models and libraries to load correctly.

Last edited by mt490; 7th December 2010 at 11:25 AM.
  Reply With Quote
Old 7th December 2010, 06:14 PM   #48
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally Posted by jcx View Post
how about discussing the thread topic
...in SPICE reality? No, thank you...

Quote:
\
for those still interested in tube theory just try some search: Langmuir-Childs law

Improved vacuum tube models for SPICE, Part 1

basically the Vgc and Vgp voltages control the current via the same nonlinear law
Quote:
The new equations for tube characteristics are phenomenological equations, that is, equations that model the behavior of physical phenomena using a reasonable number of parameters, but are not derived from fundamental physics.

__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 8th December 2010, 08:23 AM   #49
WuYit is offline WuYit  Sweden
Banned
 
Join Date: Oct 2010
Very interesting indeed, thank you for commenting on my comment, John.


Wavebourn,
many nagging questions can be answered phenomenologically...audio myths wither under the bright light of SPICE simulation...
  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
Triode in Class B or Beam Pentode in Class AB2 rsumperl Tubes / Valves 24 18th July 2010 02:24 PM
EL34 in class AB2 triode mode push-pull? ray_moth Tubes / Valves 29 8th March 2009 07:34 PM
help analysing my main AC power milen007 Everything Else 6 27th June 2008 06:15 PM
How does class AB2 sound? Craig405 Tubes / Valves 25 21st April 2008 07:48 PM
class AB2 who's using it for hifi? richwalters Tubes / Valves 8 8th March 2007 05:21 PM


New To Site? Need Help?

All times are GMT. The time now is 05:14 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright Đ1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2