testing for stability - 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 25th April 2007, 02:16 AM   #1
maxpou is offline maxpou  Canada
diyAudio Member
 
maxpou's Avatar
 
Join Date: Apr 2006
Location: Québec
Question testing for stability

Hi everybody,
i want test my poweramp with capacitive charge but i would like to know what value of cap and if i have a precaution to take, which? i don't want burn my output ( hexfet ) thank you! Maxpou
  Reply With Quote
Old 25th April 2007, 04:17 AM   #2
fab is offline fab  Canada
diyAudio Member
 
fab's Avatar
 
Join Date: Mar 2004
Location: Canada
Hi Maxpou

I suppose you have a scope otherwise...

Always put a resistor load in parallel with the cap ( 8 ohms is the standard one used and ususally represents the nominal impedance of lots of speakers).

Use an input 10 KHz Square wave and adjust the level to have an ouput of about 4V peak. Do not exceed 10 V otherwise you may have your cap to explode!! and it smells like HELL !

1) Try first with no cap in parallel
2) then try with the small value of 1 nF then increase the value with 2.2nf, 4.7nf, 10 nf, 22 nf, 47 nf, 100nf, 220nf, 470 nf, 1uf, 2.2uf.

Normally you should see different output shapes going from a perfect square wave for very low cap values (1 nf, 10nf, 22nf ...).

After that you will reach a point in caps value where sometimes the square shape may start to deteriorate a bit on the edges. It is still OK.
After that possible roughness on the edges, you will start to see overshoot (maybe 220 nF or more) but it should be damped.

Note: If you begin to see oscillation on the square wave for a specific cap value just stop the test at this value since it means your amp is not stable and depending on the oscillation it could eventually damage the amp... But you can test the other cap values to see the extent of the stability problem if any.

Just send us some pictures if you can (2 uf, 100 nf, 4.7nf for example).
Good luck!
  Reply With Quote
Old 26th April 2007, 12:06 AM   #3
maxpou is offline maxpou  Canada
diyAudio Member
 
maxpou's Avatar
 
Join Date: Apr 2006
Location: Québec
HI Fab,
thank's for your answer. but i don't have 8 ohms ressistance but 6.8 ohms, it's ok? thank you! maxpou
  Reply With Quote
Old 26th April 2007, 02:24 AM   #4
fab is offline fab  Canada
diyAudio Member
 
fab's Avatar
 
Join Date: Mar 2004
Location: Canada
6.8 ohms is OK. Anyway the speaker impedance varies a lot depending of frequency (sometimes from 3 to 18 ohms at specific frequency...). This 6.8 value should give you reliable results even to compare with other amps where the test was done with 8 ohms...

  Reply With Quote
Old 27th April 2007, 07:23 PM   #5
maxpou is offline maxpou  Canada
diyAudio Member
 
maxpou's Avatar
 
Join Date: Apr 2006
Location: Québec
Hi everybody,
i send you some pictures of test stability with my poweramp. please comment on this. thank you! Maxpou
Attached Images
File Type: jpg 10khz, 0.033uf, 10vp-p.jpg (26.1 KB, 685 views)
  Reply With Quote
Old 27th April 2007, 07:25 PM   #6
maxpou is offline maxpou  Canada
diyAudio Member
 
maxpou's Avatar
 
Join Date: Apr 2006
Location: Québec
excuse me first picture is 10Khz, 10vp-p, 0.033uf
seconde picture: 10khz, 10vp-p, 0.068uf
Attached Images
File Type: jpg 10khz, 0.068uf, 10vp-p.jpg (24.8 KB, 649 views)
  Reply With Quote
Old 27th April 2007, 07:26 PM   #7
maxpou is offline maxpou  Canada
diyAudio Member
 
maxpou's Avatar
 
Join Date: Apr 2006
Location: Québec
third picture: 10khz, 10vp-p, 0.1uf
Attached Images
File Type: jpg 10khz, 0.1uf, 10vp-p.jpg (23.0 KB, 633 views)
  Reply With Quote
Old 27th April 2007, 07:28 PM   #8
maxpou is offline maxpou  Canada
diyAudio Member
 
maxpou's Avatar
 
Join Date: Apr 2006
Location: Québec
and last 10Khz, 10Vp-p, 0.22uF load for all 6.8 ohms
Attached Images
File Type: jpg 10khz, 0.22uf, 10vp-p.jpg (26.1 KB, 646 views)
  Reply With Quote
Old 27th April 2007, 07:45 PM   #9
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi Max,
that looks like a damped 200kHz (220nF) ripple fed from a Thiele network into your R//C load.
Are you using an inductor//R in the series feed to the load?

The overshoot and ripple is looking a bit big for inductor/load interaction.
__________________
regards Andrew T.
  Reply With Quote
Old 27th April 2007, 08:25 PM   #10
maxpou is offline maxpou  Canada
diyAudio Member
 
maxpou's Avatar
 
Join Date: Apr 2006
Location: Québec
Hi Andrew,
i don't have a inductor//R in serie to the output because inductor decreased dynamic that somebody said to me. Maxpou
  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
Amp stability unclear Khron Solid State 30 3rd April 2009 06:45 AM
Stability TA2020 and T-Amp opentop Class D 2 18th May 2005 02:51 PM
stability djdamix Solid State 3 7th January 2005 07:30 AM
Aleph-X stability stefan Pass Labs 2 30th October 2002 09:00 PM


New To Site? Need Help?

All times are GMT. The time now is 08:15 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