Michael Kiwanuka's SOA PAper - 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 12th June 2013, 02:41 PM   #41
Banned
 
Join Date: Oct 2010
Location: Chigwell, Essex
Quote:
Originally Posted by GoatGuy View Post
Michael Kiwanuka,

I have read your paper somewhat thoroughly: it is impeccably done, masterful. It was my impression while reading that the paper was very likely a Senior BSEE thesis: a well said synopsis stating the various industry problems, oversights, inaccuracies, delusions and wishful ignorances, followed by a careful expository building on Fairchild's original 'improved' limiter in ways to adapt to the actual complex-plane SOA of real-world output devices and reactive speakers. You did not eschew complexity, nor fall head-over-heels for simplicity. Balanced.

Very well done.

Yet, unless I just missed it, there appears not to be an adaptive clamp on output VI product based on a heatsink mounted set of thermistors or other thermal sensors. In the many decades of designing finals, I (or really "we") have noted that thermal sensors provide a "third dimension of limit", which is especially protective for commercial-grade power amplifiers employed at live-sound outdoor events. Very often, ambient temperature can exceed 40C, and with far less-than-optimal airflow through amplifier cabinets, 60C or higher so-called cooling air is remarkably frequently encountered.

Regardless of the source though, and conditions, it is advised and worthy to include such thermal-limit protection along with the SOA circuitry, I would think. Having such circuitry certainly impacts realizable output power, but "c'est la guerre"... sound engineers aren't supposed to accidentally fuze the amplifiers if they're overdriven relative to the ambient conditions.

If I missed your thermal-angle clamping, please refer me to the page(s) where that was addressed. If not, a comment or two would be welcome!

Again, bravo!

GoatGuy

Hello,

Thanks for your kind words.

I did mention in passing on pg 16 that an amplifier should have DC offset and thermal protection.

I didn't go into details in this regard as I thought those two facets of amplifier protection extraneous to SOA protection.

However, my general view is that thermal protection, rather than being linked to SOA protection, should be associated with the circuitry that disconnects the amplifier's output from the load. I think Douglas Self has discussed such a system in one or other of his books.

Regards,

Michael.
  Reply With Quote
Old 12th June 2013, 02:55 PM   #42
pooge is offline pooge  United States
diyAudio Member
 
Join Date: May 2003
Location: Northern Va.
Quote:
Originally Posted by AndrewT View Post
But the V change is in the supply rail and thus the NFB amp manages to ignore it (sufficiently) much like it ignores all the other (bigger) V changes that are on the supply rail.
But the heating of the fuse element will distort it and make it more fragile to later events and/or mechanical "shocks", even if initial pulses don't open it.
  Reply With Quote
Old 12th June 2013, 03:14 PM   #43
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
the heating of the fuse element will distort it and make it more fragile to later events
Probably.

Look at the Krell Klone results to see how much the fuse can take and not blow, ~21Apk repeating through an F4A.
Normal music does not stress the fuse at anything like that level into the rated speaker impedance, both due to very short term transients and very few transients that get up to the maximum current capability.
__________________
regards Andrew T.
  Reply With Quote
Old 12th June 2013, 03:49 PM   #44
Bonsai is offline Bonsai  Taiwan
diyAudio Member
 
Bonsai's Avatar
 
Join Date: Jul 2003
Location: Taipei, Taiwan
Quote:
Originally Posted by michaelkiwanuka View Post
I would say a pair of 5A fuses is more appropriate for a 100W into 8ohm amplifier.
Yes, this what I use in my 100 watter nx- Amp.
__________________
bonsai
Amplifier Design and Construction for MUSIC! http://hifisonix.com/
  Reply With Quote
Old 12th June 2013, 06:42 PM   #45
diyAudio Member
 
Join Date: Dec 2010
Quote:
Originally Posted by michaelkiwanuka View Post
... my general view is that thermal protection, rather than being linked to SOA protection, should be associated with the circuitry that disconnects the amplifier's output from the load....
A overheated output stage can develop cross-conduction high enough to maintain it's high temperature. Disconnect from power supply or mains is probably better.

Last edited by franzm; 12th June 2013 at 06:46 PM.
  Reply With Quote
Old 13th June 2013, 05:36 AM   #46
diyAudio Member
 
Join Date: Feb 2006
Location: Bucharest-Romania
Please analyze the following SOA concept used in old Tandberg TR1040.
Thank you, Victor
Attached Images
File Type: jpg Tandberg TR1040.JPG (169.3 KB, 207 views)

Last edited by hpavictor; 13th June 2013 at 05:39 AM.
  Reply With Quote
Old 14th June 2013, 07:59 PM   #47
Banned
 
Join Date: Oct 2010
Location: Chigwell, Essex
I think it's a simple variation on the scheme of figure 19 on page 26.
  Reply With Quote
Old 1st July 2013, 05:15 PM   #48
Banned
 
Join Date: Oct 2010
Location: Chigwell, Essex
Quote:
Originally Posted by hpavictor View Post
Please analyze the following SOA concept used in old Tandberg TR1040.
Thank you, Victor
Wouldn't recommend it.
  Reply With Quote
Old 2nd July 2013, 06:28 AM   #49
diyAudio Member
 
Join Date: Feb 2006
Location: Bucharest-Romania
Yes sir , I Undersand .

Please , i'm interested in a mathematical example true circut protection SOA (universal) to protect the real world real output stage of a Class AB amplifier fed to
1) + / - 50 V with two pairs of transistors end power
2) + / 60 V end with three pairs of power transistors
3) + / - 70V with four pairs of power transistors end
4) + / - 85 V, with six pairs of power transistors end
5) + / - 100 V, with eight pairs of power transistors end
Heatsink will be in the worst case temperature 90 Cesius degrades due to optimum dimensioning and active cooling with fan brushless using transistors 2SA1943 end type / variant 2SC5200 or second choice MJL21194 / MJL 21193 (if needed number of transistor pairs final could be reduced by appropriate neccesary ), active duty with at least 60 degrees phase shift between the current through the load and tension.
Thanks in advance, Victor
  Reply With Quote
Old 2nd July 2013, 09:25 AM   #50
Banned
 
Join Date: Oct 2010
Location: Chigwell, Essex
Hi Victor,

Just read the article carefully from start to finish and you should be able to design your own SOA protection circuit without difficulty.

I suggest you buy the Texas Instruments TI-89 calculator to help you solve the simultaneous equations that arise. It's what I use.
  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
Michael Jackson Dead ? sandyK Music 58 20th April 2010 05:40 PM
Australian Shiraz Goes Well With Michael Brecker JimOfOakCreek Music 0 25th February 2008 02:26 PM
amorphous paper or Mu-metal paper can use for D/A chips for shielding or not???? siu sin man tho Digital Source 0 17th March 2004 12:31 PM


New To Site? Need Help?

All times are GMT. The time now is 03:22 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