Bob Cordell's Power amplifier book - Page 346 - 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 10th June 2013, 10:38 PM   #3451
wahab is offline wahab  Algeria
diyAudio Member
 
Join Date: Nov 2009
Location: algeria/france
Quote:
Originally Posted by michaelkiwanuka View Post

Anyway, I don't owe you an explanation for anything. I have demonstrated to my satisfaction the typical loop gain of the ANF current source. That is sufficient.
Granted , but do you agree that rejecting something
by let say 40dB will forcibly mandate a loop gain
of the same order.
  Reply With Quote
Old 10th June 2013, 10:59 PM   #3452
diyAudio Member
 
Join Date: Sep 2006
Quote:
Originally Posted by HarryDymond View Post
Not at all. Inductors are used as effective current sources in switch-mode circuits all the time, especially the ubiquitous clamped inductive load test circuit. What Bob said:



Is 100% true.

Once current is set up in a large inductor it behaves a lot like a current source. You know, just how a very large capacitor that has been previously energised (aka "charged") behaves a lot like a voltage source.
Excellent analogy, Harry.

Cheers,
Bob
  Reply With Quote
Old 11th June 2013, 04:38 AM   #3453
diyAudio Member
 
Join Date: Nov 2011
Location: Cooktown, Oz
Default .. from #3430

.. Michael, to get back onto something which hopefully, you don't think everyone else is wrong or cerebrally challenged

.. from #3430

ANF_loop_gain.asc
BJT_models.txt


Apart from Bias Spreader, LTP CCS, Zobels & output L, this might even be a 'real life' working amp.

Michael, can we take this as an example of your views on good practice and your target level of THD/stability? leaving out your L1 of course
  Reply With Quote
Old 11th June 2013, 08:12 AM   #3454
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by Waly View Post
............... A bipolar undegenerated LTP is obviously more sensitive to matching(s) than the degenerated case. ..........
This is why I always recommend the jig arrangement where the dut & ref are LTP connected without degen and without base stoppers.
This is very sensitive and gives good pairs that subsequently don't need trimming for output offset. <2mVdc in a +27dB amp is common.
__________________
regards Andrew T.
  Reply With Quote
Old 11th June 2013, 08:30 AM   #3455
gk7 is offline gk7
diyAudio Member
 
Join Date: Oct 2007
Location: Vienna, Austria
Quote:
Originally Posted by wahab View Post
Distorsion is by the definition creation of new frequencies...
That´s _your_ definition it seems. Phase and amplitude errors are distortions and don´t create new frequencies.

Two links:
http://www.amplifier.cd/Tutorial/Dis...ion_linear.htm
http://www.amplifier.cd/Tutorial/Dis...istortions.htm

Last edited by gk7; 11th June 2013 at 08:32 AM. Reason: Added links
  Reply With Quote
Old 11th June 2013, 10:28 AM   #3456
Banned
 
Join Date: Oct 2010
Location: Chigwell, Essex
Quote:
Originally Posted by kgrlee View Post
Michael, can we take this as an example of your views on good practice and your target level of THD/stability? leaving out your L1 of course
No.
  Reply With Quote
Old 11th June 2013, 10:28 AM   #3457
diyAudio Member
 
Join Date: Jan 2013
Quote:
Originally Posted by Bob Cordell View Post

My favorite way to implement the driven cascode is to create a replica of the feedback signal and apply that to the cascode bases. This avoids the need to mess around with the emitter circuit of the LTP.

Cheers,
Bob
Does this work as intended ?? I have found it doesnt offer the same results as the LTP emitters. D Self and Stochino say same.
Seld says in his book that the probable reason is the phase shift in the signal feedback.
  Reply With Quote
Old 11th June 2013, 10:49 AM   #3458
diyAudio Member
 
Join Date: Sep 2006
Quote:
Originally Posted by manso View Post
Does this work as intended ?? I have found it doesnt offer the same results as the LTP emitters. D Self and Stochino say same.
Seld says in his book that the probable reason is the phase shift in the signal feedback.
Hi manso,

This technique worked like a champ on my MOSFET power amplifier, but I have not tried the other technique on it.

When the replica of the feedback signal is used to drive the cascode, the signal driving the cascode is identical to the signal driving the inverting input of the LTP (assuming no differences in phase shift in the feedback network and the replica network). This means that there is an ever-so-slight difference between this technique and the technique where a sample of the LTP tail signal is used to drive the cascode bases, because the latter is the common-mode signal.

This difference will correspond to one-half of the error signal driving the LTP, which will be a very small difference, especially recognizing that the signal being used to drive the cascode is already there to cancel a second-order effect.

At audio frequencies, this difference will be very small. At higher frequencies, where the error signal is larger in a Miller-compensated amplifier, the difference will become a bit larger.

Some simulations should be able to show the differences between the two techniques.

Can you be more specific in describing how your results were different?

Can you refer me to where Stochino and Self discussed this (I did not see any reference to this in Self's 5th edition).

I'm very interested in learning more about any disadvantages in the replica cascode driving technique as compared to the other technique.

Cheers,
Bob
  Reply With Quote
Old 11th June 2013, 10:57 AM   #3459
diyAudio Member
 
Join Date: Jun 2005
Location: Zürich
Quote:
Originally Posted by Bob Cordell View Post
I'm very interested in learning more about any disadvantages in the replica cascode driving technique as compared to the other technique.
One thing to consider is that bootstrapping with a significantly bandwidth-limited signal leads to negativ input capacitance of the bootstrapped transistor. Unless adressed, this may cause instability.

Samuel
  Reply With Quote
Old 11th June 2013, 01:48 PM   #3460
diyAudio Member
 
Join Date: Jan 2013
Hi Bob

Indeed your results may be somewhat different because of topology and compensation used.
My results were obtained through simulation of the regular blameless topology. If no-one posts the Self reference before Ill post it tommorrow. If I remember correctly it is in his fifth edition where he took actual measurements of this technique.
  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 02:48 AM
best audio amplifier book?? Bouvett Everything Else 30 13th August 2012 02:43 AM
Amplifier Design Book pixie Everything Else 27 11th June 2010 08:36 PM
Project 11.1 from Slone "High-Power Amplifier" Book Karl71 Solid State 46 6th October 2008 03:47 AM
book-audio power amplifier by Douglas Self mikee12345 Solid State 8 16th November 2003 01:16 AM


New To Site? Need Help?

All times are GMT. The time now is 05:27 PM.


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