CFA Topology Audio Amplifiers - 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 13th August 2013, 02:46 AM   #1
Bonsai is offline Bonsai  Taiwan
diyAudio Member
 
Bonsai's Avatar
 
Join Date: Jul 2003
Location: Taipei, Taiwan
Default CFA Topology Audio Amplifiers

This thread is where we can discuss CFA and compare it to VFA in a friendly and constructive manner.
__________________
bonsai
Amplifier Design and Construction for MUSIC! http://hifisonix.com/
  Reply With Quote
Old 13th August 2013, 02:52 AM   #2
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Great.... There are some miss-conceptions and significant differences might start with.

-RNM
  Reply With Quote
Old 13th August 2013, 02:58 AM   #3
Bonsai is offline Bonsai  Taiwan
diyAudio Member
 
Bonsai's Avatar
 
Join Date: Jul 2003
Location: Taipei, Taiwan
A quick summary

CFA: amplifier topology that inherently supports fast rise/fall times and wide bandwidths. Distortion performance with the basic topology incl. EF3 can meet sub 10 ppm levels at 20 kHz. PSRR not as good as VFA topology, requiring additional filtering and regulation especially of the front end buffer/level shifter stage. Considered easy to compensate. Of interest in audio are the wide loop bandwidths, in some cases up to 40 or 50 kHz. Typical upper loop gain in the 60 dB range.

VFA: amplifier topology that in MC guise supports moderate to fast slew rates. LF dominant pole required to ensure unconditional stability. Alternative comp schemes allow slew rates and rise times to match CFA - eg MIC. PSRR performance of the basic topology better than CFA; noise performance considered better in some cases. Distortion performance when using advanced comp techniques and EF3 can achieve low single digit ppm levels (20 kHz). Typical LF OLG in 100dB plus range, dropping at 20 dB/decade such that at 20 kHz, 50 dB of loop gain may be available using standard MC. This figure may be increased using alternative comp schemes like MIC or TMC.
__________________
bonsai
Amplifier Design and Construction for MUSIC! http://hifisonix.com/

Last edited by Bonsai; 13th August 2013 at 03:06 AM.
  Reply With Quote
Old 13th August 2013, 10:13 AM   #4
Banned
 
Join Date: Oct 2010
Location: Chigwell, Essex
Quote:
Originally Posted by Bonsai View Post
Alternative comp schemes allow slew rates and rise times to match CFA - eg MIC


Typical LF OLG in 100dB plus range, dropping at 20 dB/decade such that at 20 kHz, 50 dB of loop gain may be available using standard MC. This figure may be increased using alternative comp schemes like MIC or TMC.
Actually, MIC, or input inclusive compensation does not allow more major loop gain than ordinary Miller compensation.

Secondly, I suspect, but haven't examined this yet, that the compensation network that is required to make the input inclusive compensation loop stable may worsen PSRR dramatically.

My suspicions are founded in the fact that the similar shunt compensation network required to make the minor loop stable with Jolly-McCharles input cascode inclusive compensation ruins the PSRR.
  Reply With Quote
Old 13th August 2013, 11:44 AM   #5
diyAudio Member
 
buzzforb's Avatar
 
Join Date: Oct 2010
Location: Burlington, NC
Esperado,
In your summation of how you want the thread to go, you seemed to close the argument on the possibility that the VFA could sound better than the CFA. While I am not saying whether this is true or not, an openminded conversation that begins with a close minded statement seems interesting. I have listened to both the TSSA1.6 from member Sonya and the VSSA that I proto'ed using laterals. I preferred the TSSA over the VSSA. I agree that the amp "sound" extremely fast, with good pace and lots of air. I did not think that either performed as well in terms of tone or overall body in comparison to some Class A VFB amps I have built. I will proto the SSA next to see if it comes closer in this regard. I thought the VSSA would step closer than the TSSA, but it seemed to only give up some of its better capabilities in comparison, without gaining anything in return. This is not to say it is not an excellent amp, as I am just talking about personal taste. Of course we all know that everyone likes different colors, although I believe blue is the best.
__________________
...Shape the sound , Man!
  Reply With Quote
Old 13th August 2013, 11:53 AM   #6
diyAudio Member
 
Join Date: Sep 2006
Quote:
Originally Posted by Bonsai View Post
This thread is where we can discuss CFA and compare it to VFA in a friendly and constructive manner.
Thanks for opening up this thread, Bonsai. It is a good topic for discussion.

Cheers,
Bob
  Reply With Quote
Old 13th August 2013, 12:02 PM   #7
mcd99uk is offline mcd99uk  United Kingdom
diyAudio Member
 
Join Date: Mar 2008
Location: UK
All we need now are the posts moved from D Self's thread to here.
  Reply With Quote
Old 13th August 2013, 12:04 PM   #8
diyAudio Member
 
Join Date: Sep 2011
Somehow I suspect if I would put my MF80 VFA project (which had been designed for speed as well, with a fast output stage configuration and is capable of slewing in excess of 200V/us) inside a black box with a label saying "CFA MOSFET AMP", and invited all CFA proponents to listen to it, that the amp would receive universal acclaim.
__________________
Negative Feedback: The Need for Speed
  Reply With Quote
Old 13th August 2013, 12:06 PM   #9
diyAudio Member
 
Join Date: Sep 2006
Quote:
Originally Posted by michaelkiwanuka View Post
Actually, MIC, or input inclusive compensation does not allow more major loop gain than ordinary Miller compensation.

Secondly, I suspect, but haven't examined this yet, that the compensation network that is required to make the input inclusive compensation loop stable may worsen PSRR dramatically.

My suspicions are founded in the fact that the similar shunt compensation network required to make the minor loop stable with Jolly-McCharles input cascode inclusive compensation ruins the PSRR.
I believe you are correct in that MIC does not allow greater global loop ULGF than ordinary MC.

MIC does not necessarily destroy PSRR, and in some cases may improve it. Take a look at the MIC implementation in my MOSFET power amplifier with error correction, http://www.cordellaudio.com/papers/MOSFET_Power_Amp.pdf. The MIC loop compensation is accomplished with a differential shunt series R-C across the differential outputs of the IPS. This thus does not compromise PSRR. Moreover, the MIC Cdom is referenced to signal ground on both sides, which eliminates one of the major causes of PSRR degradation in standard MC, namely that one side of Cdom is referenced to the power supply rail while the other side is referenced to signal ground (i.e., the VAS output node).

Cheers,
Bob
  Reply With Quote
Old 13th August 2013, 12:17 PM   #10
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Carried over

Quote:
Originally Posted by michaelkiwanuka View Post
There is absolutely no way your amp. can have 80dB of loop gain at 20KHz and be stable. No way at all.
Mine has and more and is 100% stable.
Attached Images
File Type: jpg M1 OLG plot.JPG (91.5 KB, 4677 views)
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  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
nx-Amplifier: 100 W CFA topology Amp Bonsai Solid State 35 9th July 2013 04:34 PM
Cambridge Audio 740A topology lduarte1973 Chip Amps 5 27th June 2011 07:32 AM
crossfire cfa-602, car audio amp problem tuneman Car Audio 29 23rd September 2010 05:08 AM
crossfire cfa-602, car audio amp problem tuneman Solid State 1 11th September 2010 01:51 PM
pro amplifiers vs. home audio amplifiers bonsai171 Solid State 26 25th February 2004 08:24 PM


New To Site? Need Help?

All times are GMT. The time now is 08:43 AM.


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