Go Back   Home > Forums > Amplifiers > Class D

Class D Switching Power Amplifiers and Power D/A conversion

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 11th September 2007, 06:44 PM   #1
diyAudio Member
 
Join Date: Jul 2004
Location: Seattle USA
Question class-d behavior at clipping

What's the behavior of class-d at the onset of clipping all the way up to full rail pegging clipping?

Not just with a sine wave but with full spectrum music? That is the higher frequencies are riding on the lower frequencies. As described at:
http://www.st-andrews.ac.uk/~jcgl/Sc...ing/page3.html

It would seem that at these extremes the pre-filter feedback would be more stable?

I can imagine that these lower powered class-d amplifiers do clip quite a bit in real life use and no one is the wiser up until it hits some extreme.

Just curious.
  Reply With Quote
Old 11th September 2007, 07:40 PM   #2
poynton is offline poynton  United Kingdom
diyAudio Member
 
poynton's Avatar
 
Join Date: Mar 2005
Location: A life on the ocean waves when I'm not at home in N. Wales (but I'm not Welsh so no sheep jokes!)
Do class -D amps pwm "clip" ?
  Reply With Quote
Old 11th September 2007, 10:24 PM   #3
BWRX is offline BWRX  United States
diyAudio Moderator Emeritus
 
Join Date: Jan 2005
Location: Pennsylvania
Of course class d PWM amps clip. As you approach clipping the THD goes up and is easy to detect, very much like a class ab amplifier.
__________________
Brian
  Reply With Quote
Old 13th September 2007, 12:28 AM   #4
diyAudio Member
 
Join Date: Jul 2004
Location: Seattle USA
Except class-d has an output filter, and it only has a couple of output devices. And they are normally just switched on and off, so other than current they aren't stressed.

Maybe the window of low THD to an unusable level is larger with class-d?

Maybe it just doesn't matter. If it sounds bad turn it down.
  Reply With Quote
Old 13th September 2007, 04:30 AM   #5
Pano is offline Pano  United States
diyAudio Moderator
 
Pano's Avatar
 
Join Date: Oct 2004
Location: Milliways
Blog Entries: 4
I can only speak to Tripath and TI chips, but they certainly clip, and they clip hard.

Of course it's not really the output devices that are clipping, as the are simply on or off (idealy). So it must be the comparitor circuit that's clipping - or maybe the input circuit, but I would bet on the comparitor.

The Tripath chips have a small region of "soft clipping" but it's a narrow window. Push beyond that and the crests of a sine wave just get chopped off. It does not sound nice. You can see it happening to musical peaks, too. The clips show up as bright spots at the top of waveform when seen on an o'scope.

Some of the very fast clipping you won't even notice, but push it too far and it sounds harsh. Perhaps a class-d amp could/should be built with some form of peak limit to avoid the clipping.
__________________
Take the Speaker Voltage Test!
  Reply With Quote
Old 13th September 2007, 04:42 AM   #6
BWRX is offline BWRX  United States
diyAudio Moderator Emeritus
 
Join Date: Jan 2005
Location: Pennsylvania
Quote:
Originally posted by raintalk
If it sounds bad turn it down.
That applies to almost all things related to audio
__________________
Brian
  Reply With Quote
Old 13th September 2007, 12:03 PM   #7
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
Some higher-order feedback loops can behave worse than just chopping off the tops and bottoms. They can somehow "stick to the rails" and go back to normal by crossing some instability zone which may add some additional non-harmonic components.

Regards

Charles
  Reply With Quote
Old 13th September 2007, 12:34 PM   #8
diyAudio Member
 
Ouroboros's Avatar
 
Join Date: Dec 2003
Location: Nottingham UK
UCD-style self-oscillating amplifiers exhibit a sharp increase in distortion as the modulation index goes above (approximately) 85%. Well designed ones clip cleanly, although I have had prototypes exhibit some 'raggedness' on the output just before clipping.
  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
Chip amps and clipping/protection behavior danielwritesbac Chip Amps 4 28th March 2008 04:58 AM
Odd transformer behavior badman Everything Else 3 23rd August 2006 07:03 PM
Odd behavior of preamp Dwiel Instruments and Amps 7 29th July 2006 07:54 PM
Clipping Class D ? Joules Class D 31 19th January 2006 07:27 AM


New To Site? Need Help?

All times are GMT. The time now is 06:26 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