Bob Cordell's Power amplifier book - Page 13 - 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 12th August 2010, 04:03 PM   #121
AndrewT is online now AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by Bob Cordell View Post
Obviously, MOSFETs like more bias current, and that is a price to be paid for good MOSFET output stage linearity. This will result in the amplifier running hotter in the idle state,
Borbely agrees with you. He specifies a minimum of 500mA of output bias current irrespective of how many pairs are in the output stage.
He also specifies a minimum of 100mA of output bias current for each pair.
__________________
regards Andrew T.
  Reply With Quote
Old 12th August 2010, 05:40 PM   #122
CBS240 is offline CBS240  United States
diyAudio Member
 
CBS240's Avatar
 
Join Date: Aug 2005
Location: K-town
I agree as well. I demonstrated the effect of low bias over a year a go here with an HEC output follower stage comparing the difference in error between very low bias and 300mA. Big difference, but even with 300mA you can still see a Gm droop as indicated by the subtle change in slope of the error signal at the crossover.
__________________
All the trouble I've ever been in started out as fun......
  Reply With Quote
Old 12th August 2010, 07:44 PM   #123
diyAudio Member
 
DouglasSelf's Avatar
 
Join Date: Mar 2007
Hi Bob

Looks like I have competition! Congratulations on coming to the end of what must have been a demanding project- I know just how much work is involved in putting together 600+ pages of hard fact.

I look forward keenly to reading it. I have my next book coming out about the end of the year- how about swopping signed copies?

The best of luck with your book- I wish it success.
__________________
Douglas Self
  Reply With Quote
Old 12th August 2010, 10:11 PM   #124
diyAudio Member
 
Join Date: Sep 2006
Quote:
Originally Posted by DouglasSelf View Post
Hi Bob

Looks like I have competition! Congratulations on coming to the end of what must have been a demanding project- I know just how much work is involved in putting together 600+ pages of hard fact.

I look forward keenly to reading it. I have my next book coming out about the end of the year- how about swopping signed copies?

The best of luck with your book- I wish it success.
Hi Doug,

Thanks for your kind words. I'm sure you do know how much effort is involved! Another book the end of this year? How do you do it? You are not only very prolific, but you turn out such high-quality material. I'm not sure my dear wife will ever let me write another book!

Best regards and thanks again,

Bob
  Reply With Quote
Old 14th August 2010, 02:07 PM   #125
diyAudio Member
 
Join Date: Sep 2006
Default MOSFET asymmetrical source resistors

Here is some interesting data from the book regarding the THD performance achievable with class AB MOSFET output stages when asymmetrical source resistors are used to reduce relative transconductance droop and better match P-channel and N-channel transconductances. It is especially notable how the performance compares to an analogous BJT output stage with the same total bias current.

The output stage for which 20 kHz THD is shown below includes four pair of Toshiba 2SK1530/2SJ201 power MOSFETs. Each pair was biased at about 160 mA. The N-channel devices had 0.33-ohm source resistors while the P-channel devices had 0.15-ohm source resistors. The output stage was simulated using EKV models for the MOSFETs. The performance shown is the open-loop distortion of the output stage alone when driven with an ideal driver. The output stage is designed for 200 W at 8 ohms or 400 W at 4 ohms.

Cheers,
Bob
Attached Images
File Type: png MOSFET Output.png (9.2 KB, 629 views)
File Type: png BJT Output.png (8.5 KB, 613 views)
  Reply With Quote
Old 16th August 2010, 07:03 PM   #126
Account disabled at member's request
 
Join Date: Oct 2008
Hi Bob

First of all congratulations with your book, if it’s written in the same wise and technical way that your posts at this forum and your emails I’m sure it’s going to be a classical “must have” for everybody that is interested in the subject “Audio amplifier design”.

Questions:
1. Do you have a plot showing the THD on the MOSFET ops, when you’re using the same source R for the N and P devices? It would be nice to compare it with the plot with different source resistors.

2. When you are using different values on the source resistors, is the reduction in the THD mostly 2H, 3H or is the reduction evenly distributed.

3. Have you done experiments with different values on the gate stopper resistors on N and P devices?

Cheers
stinius
  Reply With Quote
Old 16th August 2010, 08:30 PM   #127
diyAudio Member
 
Join Date: Jul 2008
Send a message via AIM to SpeakerScott Send a message via MSN to SpeakerScott Send a message via Yahoo to SpeakerScott
Default Pre-ordered mine a week or so ago....

When the thread had just started...just now got around to posting about it.

Thank you so much for taking the time to add to the published works about audio amplifiers...

Scott
__________________
http://speakerscott.tumblr.com/
  Reply With Quote
Old 16th August 2010, 08:52 PM   #128
diyAudio Member
 
Stormrider's Avatar
 
Join Date: Apr 2006
Location: Connecticut
Blog Entries: 2
Send a message via AIM to Stormrider Send a message via MSN to Stormrider
Preordered mine yesterday... Glad I caught the sale price, but I would have paid the full price anyway. I'm sure it's going to be well written and very interesting. Looking forward to it!
__________________
AJ
  Reply With Quote
Old 17th August 2010, 05:49 AM   #129
diyAudio Member
 
panson_hk's Avatar
 
Join Date: Aug 2005
Blog Entries: 10
made pre-order today! Can't wait to read it!
  Reply With Quote
Old 17th August 2010, 09:12 AM   #130
diyAudio Member
 
Join Date: Apr 2007
Hello mr Cordell

Congratulation for your book.

About mosfet bias, Nelson Pass did an interesting test and graph about it, here it is.

Bye

Gaetan
Attached Images
File Type: gif Nelson Pass-bias-mosfet.gif (14.1 KB, 484 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
Another realization of Bob Cordell's THD Analyzer giulianodes Equipment & Tools 37 9th October 2013 03:48 AM
best audio amplifier book?? Bouvett Everything Else 30 13th August 2012 03:43 AM
Amplifier Design Book pixie Everything Else 27 11th June 2010 09:36 PM
Project 11.1 from Slone "High-Power Amplifier" Book Karl71 Solid State 46 6th October 2008 04:47 AM
book-audio power amplifier by Douglas Self mikee12345 Solid State 8 16th November 2003 02:16 AM


New To Site? Need Help?

All times are GMT. The time now is 10:14 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