Is the CFB topology superior, and why? - Page 26 - diyAudio
 Is the CFB topology superior, and why?
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diyAudio Member

Join Date: Sep 2006
Quote:
 Originally Posted by catalin Why not satisfy both cfb and vfb listeners ? a wonderfull sziklai My ears are delighted with 60db of CFB and 20 db of vfb Also it is possible to equalise the cfb and vfb factor by making equal the ratios: R15/R2 = R5/R8 . If we want to have the cfb dominant we can decrease R15 to 10kohm for example and put in series a capacitor of 22uF to minimise the voltage drift in dc .
That is CFB, homeopathic fashion, a bit like so-called "tube amplifiers" with a single tube and just the heather connected: the two loops are neither cascaded nor nested, they operate concurrently which means that the ever so slightly stronger one dominates completely over the other.
Translated in CFB terms, the equivalent value of the VFB resistor is ~40K, against the 220K for CFB.
As for the Bode plots, you obviously made a mistake somewhere.
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diyAudio Member

Join Date: Jun 2007
Quote:
 Originally Posted by Elvee As for the Bode plots, you obviously made a mistake somewhere.
Elvee ,the plots are "The gain and phase without and with 220k from inverting input to ltp collectors"
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Banned

Join Date: Jul 2011
Location: Portugal
Quote:
 Originally Posted by Elvee they operate concurrently which means that the ever so slightly stronger one dominates completely over the other.
So, how can-you explain ivanlukic and catalin can feel any change ?
Why don't you think to use this nice idea (concurrent FB), varying their percent, in order to explore more deeply the sonic difference between the two FB configurations ?
It is a VERY good idea.
Why, always, a so negative attitude ? Have you been mistreated by some CFB during your childhood ?

Last edited by Esperado; 2nd November 2012 at 06:28 PM.

diyAudio Member

Join Date: Jun 2007
Quote:
 Originally Posted by dadod Haw did you came to those values for CFB and VFB, and at what frequences? In your schematic R15 is 330k and you states 60db of the CFB(dominant) and later you said to make CFB dominant decrease R15 to 10k. It looks like your claims are unsupported. I like your idea, but you have to support your claims. dado
Dadod ,Thd is measured at 20khz with 10 harmonics at 1Watt in 4 ohms.I often listen music at 1-3 watt .In my schematic R cfb=220kohms .The amp in pure open loop (without cfb and vfb ) has almost 110 db gain .From here the 220k/680ohms=323 which means 50db of cfb gain .The difference from 110 and 50 is exactly 60db feedback factor.So without vfb we have an "open loop gain" of about 50dB .Introducing vfb we have 10k/330 ohms = gain of 30db .The difference from 50db to 30 is 20db feedback factor of vfb .
So what is unsupported ?
I will post simulations later on sziklai topic .
Thank you !
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"please try to listen to some music through the amplifier instead. Life is so short ..."

 2nd November 2012, 07:01 PM #255 diyAudio Member   Join Date: Jul 2010 Location: Cacak Esperado, It is great idea to listen to the changes of sound by changing the ratio between cf and vf in Catalin's amp. Probably one could use pots instead of fixed resistors to tune the circuit to personal taste.
diyAudio Member

Join Date: Apr 2006
Location: Zagreb
Quote:
 Originally Posted by catalin Dadod ,Thd is measured at 20khz with 10 harmonics at 1Watt in 4 ohms.I often listen music at 1-3 watt .In my schematic R cfb=220kohms .The amp in pure open loop (without cfb and vfb ) has almost 110 db gain .From here the 220k/680ohms=323 which means 50db of cfb gain .The difference from 110 and 50 is exactly 60db feedback factor.So without vfb we have an "open loop gain" of about 50dB .Introducing vfb we have 10k/330 ohms = gain of 30db .The difference from 50db to 30 is 20db feedback factor of vfb . So what is unsupported ? I will post simulations later on sziklai topic . Thank you !
When you said 110db of gain it is actually Oen Loop Gain(OLG). Difference between OLG and Close Loop Gain(CLG) is called Loop Gain(LG) or acctual Negative Feed Back(NFB) gain.
You can't calculate NFB one after another separately as both NFB are in parallel in some way, and your calculation is not good.

diyAudio Member

Join Date: Apr 2006
Location: Zagreb
Quote:
 Originally Posted by Esperado So, how can-you explain ivanlukic and catalin can feel any change ? Why don't you think to use this nice idea (concurrent FB), varying their percent, in order to explore more deeply the sonic difference between the two FB configurations ? It is a VERY good idea. Why, always, a so negative attitude ? Have you been mistreated by some CFB during your childhood ?
Whay do you think that Elvee attitude is negative, his explanations are technicaly good, but you can't accept different explanation then yours. I think your attitude is negative and a bit aggressive.

Banned

Join Date: Jul 2011
Location: Portugal
Quote:
 Originally Posted by dadod You can't calculate NFB one after another separately as both NFB are in parallel in some way, and your calculation is not good. dado
I believe that too.

Banned

Join Date: Jul 2011
Location: Portugal
Quote:
 Originally Posted by dadod his explanations are technically good
"which means that the ever so slightly stronger one dominates completely over the other" ?

I'm not aggressive in anyway, don't you feel the smiley behind my words?
I have the greatest respect for his way to explore new topologies. I just wonder why he is so upset about CFB, and always in a negative way, while near all which had tested-it agree with what it brings on the sonic scene.
And it is not a crusade, from my side, i really do not care, everybody do as he feels.

Last edited by Esperado; 2nd November 2012 at 07:55 PM.

diyAudio Member

Join Date: Sep 2006
Quote:
 Originally Posted by catalin Elvee ,the plots are "The gain and phase without and with 220k from inverting input to ltp collectors"
That's what I said, a mistake: measuring the OLG of a circuit block with a third terminal injecting something into the said block is wrong.

Quote:
 Originally Posted by Esperado So, how can-you explain ivanlukic and catalin can feel any change ?
OK, if you venture into this field, how do you explain audiojoy can feel any change (and this is a relatively gentle one, I spare you the negative-energy absorption gems, the breaking-in of mains cables, and probably some others I don't even know of, and I prefer not to)
Piezobee -a very simple and cheap power filter
Quote:
 Why don't you think to use this nice idea (concurrent FB), varying their percent, in order to explore more deeply the sonic difference between the two FB configurations ?
Yeah why not, but then do it properly, with at least a basic understanding of the circuits and maths involved, and even more importantly, with proper metrics to decide which one is better, and proper methodology to remove statistical noise from the results.
Quote:
 Why, always, a so negative attitude ? Have you been mistreated by some CFB during your childhood ?
So far, I have been confronted by a CFB fan club whose main argument can be thus summarized: "CFB is better because I like it" (and I find it sounds better, but I am not ready to test it in a blind test)
A bit tiring, isn't it? Especially when you realize that all the real progresses in the audio/acoustical reproduction fields have not been made by people listening narcissisticly for hours to their creations, but by people ready to ignore their own feelings and gather patiently evidences, create models, theories, topologies, benchmarking systems, etc.
Much less glamorous and much more hard work, and then some guy arrives, picks and chooses a bit or another of various theories to their own convenience and claims he has discovered something.

One thing has to be remembered at all times: without at least a semblance of metric, no progress is possible (except in religion, of course but it is exempted). Audio is no exception to that rule.
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Last edited by Elvee; 2nd November 2012 at 08:34 PM.

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