combining class A and class D - Page 2 - diyAudio
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 1st February 2008, 06:15 AM   #11
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
The carrier residual being fed through Miller capacitance itself is not the problem, carriers are not a bad thing, the problem is that Miller capacitance is highly non linear, and in the case of bipolars, current gain and Vbe are also strongly dependent on Vce in the low region and they get modulated by residuals in a non-linear fashion.

I prefer the plain class D approach. You can get half power THD in the 0.0xx range with proper design, and you can build 200W amplifiers with a pair of TO-220 MOSFETs without heatsink
__________________
I use to feel like the small child in The Emperor's New Clothes tale
  Reply With Quote
Old 1st February 2008, 07:03 AM   #12
405man is offline 405man  Scotland
diyAudio Member
 
Join Date: Dec 2003
Location: South Lanarkshire near Glasgow Scotland
In the link at the bottom of this page

http://quad405.com/

"Feedforward Error Corrections in Audio Power Amplifier" by John Vanderkooy and Stanley P. Lipshitz" The last couple of pages deal with the combination of Class A + Class D and offer some analysis

Stuart
  Reply With Quote
Old 1st February 2008, 08:11 AM   #13
GK is offline GK  Australia
Account disabled at member's request
 
Join Date: Jan 2006
Quote:
Originally posted by Eva
The carrier residual being fed through Miller capacitance itself is not the problem, carriers are not a bad thing, the problem is that Miller capacitance is highly non linear, and in the case of bipolars, current gain and Vbe are also strongly dependent on Vce in the low region and they get modulated by residuals in a non-linear fashion.

Carrier feed-through is a problem if (for the class-A stage) you want to employ conventional linear design techniques utilising large amounts of global negative feedback and the highest unity loop gain crossover frequency (conflicting with an adequate phase margin) for adequate loop gain at 20kHz to get a degree of linearity and IMD performance typical of a well designed conventional class A amplifier.
If you are not going to address this issue, or design along such lines, then you might as well forget about bothering with a class-A add-on for you class D amplifier altogether because the net result will be a very (if at all) marginal improvement indeed.
And as I already mentioned, in a rail tracking amplifier the nonlinearly of the collector-base (drain-gate) capacitance is largely mitigated due to the fact that the ratio of variation of Vce (Vds) and the degree of Cob variation is minimal (compared to a conventional amplifier) - provided that Vce (Vds) is kept above the threshold at which fT rapidly degrades.
  Reply With Quote
Old 1st February 2008, 12:07 PM   #14
diyAudio Moderator Emeritus
 
lumanauw's Avatar
 
Join Date: Oct 2002
Location: Bandung
Send a message via Yahoo to lumanauw
Glen, EVA,

Thanks for the input here.

For efficiency, what do you think about classG such can be seen on TDA7294 datasheet? The dissipation is about halved, without the difficulty of making classD part (classD is not easy )
  Reply With Quote
Old 1st February 2008, 01:38 PM   #15
diyAudio Member
 
Join Date: Aug 2004
Location: Uppsala,Sweden
The idea was eventually implemented in the Audio Physic Strada mono blocks some years ago. I donīt know what happened to these amps that were quite expensive and got were good reviews.
I remember that they used silk spun litz wire for the output chokes though as they claimed the sound of the amps benefited from it...
http://forum.audiogon.com/cgi-bin/fr...id&zzDinos&4&5
__________________
Without wonderment,no life.
  Reply With Quote
Old 1st February 2008, 05:52 PM   #16
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
Quote:
Originally posted by lumanauw
Glen, EVA,

Thanks for the input here.

For efficiency, what do you think about classG such can be seen on TDA7294 datasheet? The dissipation is about halved, without the difficulty of making classD part (classD is not easy )
"Chopping" the rails in that way is not particularly advantageous in terms of distortion or circuit complexity. In the end it's not that hard to go the plain class D way.
__________________
I use to feel like the small child in The Emperor's New Clothes tale
  Reply With Quote
Old 2nd February 2008, 11:17 AM   #17
diyAudio Member
 
Join Date: Jun 2005
Location: Sunderland
this subject was the title of a couple of AES papers in Munich and amsterdam in the late 90's when Karsten Neilson was doing the Mecc papers, IIRC people from phillips and a japanese concern were presenting on it.
it all seemed to die a death due to the increased performance of direct class d and digital in amplifiers with bitstream to delta sigma or pwm direct conversion in dsp.
I will try and dig the papers out, maybe some of the problems are solved with faster and better fets available now?
__________________
Anthony C Smith MAES MinstSCE
-I think rain is wet so who am I to Judge-
  Reply With Quote
Old 3rd February 2008, 07:27 PM   #18
Steven is offline Steven  Netherlands
diyAudio Member
 
Steven's Avatar
 
Join Date: Oct 2003
Location: The Netherlands
Default Switch mode assisted linear amplifiers

There are plenty of papers on this subject. Many not available on the web for free; most are AES papers or IEEE papers. Just as a starter (from what is available on the web):

http://www.ramsete.com/Public/AES-116/Tandem-AES116.pdf
http://innovexpo.itee.uq.edu.au/1999...ence_paper.pdf
http://innovexpo.itee.uq.edu.au/2003...194/thesis.pdf
http://innovexpo.itee.uq.edu.au/2000...972/thesis.PDF
http://www.ece.uvic.ca/~ece499/2005b/group09/PR2.doc
http://www.ece.uvic.ca/~ece499/2005b/group09/final.doc
http://innovexpo.itee.uq.edu.au/1999...ley/thesis.pdf
http://circuit.kaist.ac.kr/upload_fi...fer/1997_2.pdf
http://doc.utwente.nl/14521/1/power-...lifier-zee.pdf
http://doc.utwente.nl/14149/1/t000000d.pdf
http://doc.utwente.nl/15956/1/01471022.pdf
http://www.eserviceinfo.com/download...YST-SW800.html

Steven
__________________
The Analog Art shows no sign of yielding to the Dodo's fate. The emergence and maturation of monolithic processing finesse has perhaps lagged a bit behind the growth of the Binary Business. But whereas digital precision is forever bounded by bits, there is no limit excepting Universal Hiss to the ultimate accuracy and functional variety of simple analog circuits. - Barry Gilbert, 1973
  Reply With Quote
Old 27th April 2009, 06:52 PM   #19
diyAudio Member
 
courage's Avatar
 
Join Date: Feb 2006
Location: Neverland
I notice that it's been a while since the last post here, but I guess some progress has been made in exploring ideas/desings concerning Class A-D desings. I recently started reading about it.

If anyone by chance has a complete schematic of the Audio Physic Strada digital mono amp, I would be very interested. I contacted them today, but the project has been abandoned so they could concentrate on their core business; speakers. They also do not have the schematics of the Strada anymore, sadly.

Any other similar or improved design combining the best of both worlds is also welcome.

Thanks in advance.
__________________
Franklin
  Reply With Quote
Old 28th April 2009, 07:19 AM   #20
diyAudio Member
 
Join Date: Jun 2004
Location: California, USA
IMO, Eva completely covered the topic by stating how simple a class D amp can be while giving you adequate (if not similar or better) audio performance. Why in the world would you possibly want to design 3 (OK, 2.5 power converters instead of just 1?!? Sure, it was a cool idea many years ago but class D has advanced since then and this idea is just plain outdated. I wholeheartedly agree with Bruno when he said something to the effect that anyone who can design a good class D amp can design a great linear amp. So why not just cut right to the chase? Again, just my opinion.

But don't let me deter you as a learning experience. There's a lot of good stuff to learn by doing a project like this, if you're up to it.
  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
1500W RMS Class D PCB - which Class D Driver Chip is it ? mosfetsound Class D 11 1st April 2011 11:17 AM
Can a Class AB PP amp be said to be operating in Class A at low signal levels? ray_moth Tubes / Valves 19 23rd January 2009 07:52 PM
How about a round-up of Class A kit power amps, or collectable vintage class A? Brisso57 Solid State 4 14th February 2007 10:30 AM


New To Site? Need Help?

All times are GMT. The time now is 07:42 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright Đ1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2