CFA Topology Audio Amplifiers

Lazy not talking about the source output, but if you attach a passive volume control in front of yours/my circuit, then the typical 1K/330pF input filter roll-off varies a lot with the volume setting. If you look at how Sonny's input diamond the makes the input filter integrated in a very clever way. This is a true practical benefit of the diamond input.

I know exactly what you mean, I know something about impedances vs. frequency etc., but volume regulation is normally a part of a source unit.

Diamond input thanks, but no thanks. Someone said it is good for easy listening songs. :D
 
Diamonds are really good.. simply the best material for bass-membranes.:) I fail to see the benefit of the input diamond in a CFA amplifier, unless it's for making the input-filter independent of the the series resistance of the source. (as in having an unbuffered volume control in front of the amplifier)

It allows implementations and improvements to be made to the diamond buffer, for example feedforward and slew enhancement. Feedforward not only increases slewrate considerably but also reduces dissipation in the followers of the diamond. Have a look at the amp that Ostripper posted, a member showed a dissipation problem that could occur.
 
Still doesnt answer why so many companies and people hear and like CFA best.

I'm curious too...
Many person who hear my amps, VFA and CFA, they notice the different. They like CFA than VFA and they do not know about electronics. Usually they comment when hear my CFA, " hey, the cymbal is so real..."

Hehe may be I'm the only one who can recognize which amp is a CFA in a blind test :D

One reason for company like Accuphase to adopt CFA is probably the hello effect of CFA sound. It can impress listener in short time listening. That character alone is positive, but as a whole amplifier, it doesn't guarantee a better sound. Later on I believe that CFA users will start to discuss what is the best preamp (or buffer) to match with the amp.

In the old days when I didn't know how to design an amp, the resistance in the FB is one of several factors that I use to judge the quality of an amp from looking at the schematic only. Smaller resistance just sound better. I often change 56K/560 to become 47K/470 for example. Of course you can't just lower the resistance like that without risking stability.
 
Just an observation over time... I guess it was repeated many times and in many ways -- what? That when ever there was an advantage or a difference displayed, the VFA (or CFA) camp figures they can match it if they just change this and that around..... Over and over here to the point where my brain said - "I've heard this pattern before".

In the beginning of this, we wanted to know what a CFA was... the pro-con and configuration which gives it the pro's and con's. Now the two have been tweaked to become so much alike that there is almost no difference between them.

Its just something I noticed throughout this thread: The competitive back and forth has produced potential matching solutions to just about everything which had traditionally made VFA and CFA more different out in the field/market place. Hmmmm. Strange.

Still doesnt answer why so many companies and people hear and like CFA best. But, then if more VFA were made as descibed here, the gap might actually be almost nil.

Except for that pesky input stage.


Thx-RNMarsh

Hi Richard,

These are good observations, and touch on a number of things going on on this thread and with VFA vs. CFA.

First, there are those who are deeply interested in understanding the technical workings of, and differences between VFA and CFA. Which produces the better specs in one area and maybe trades off something in another area, and why. Even though this aspect is fairly objective and simulatable/measurable, we even have different perspectives here among the participants. It is always fascinating to try to do apples-apples.

The second is the subjective matter, which is much more difficult to address in a thread like this. One participant cannot walk in the subjective shoes of another. Subjective stuff is difficult in audio, whether we are talking about anecdotal results of informal listening tests by us, by reviews by reviewers, or by blind tests. But let me say this, if we buy into the view that there are audible differences in audio components that cannot be explained by the measurements that are commonly done, then it is still possible that a significantly different topology like CFA can sound different (maybe better, at least to some ears).

For example, if we can allegedly hear differences in speaker cables, interconnects and power cords, where there is not a lot of measurable data to explain it, then it is not hard to think that there may be audible differences between two quite different amplifier topologies.

There are those who think no-NFB amplifiers are superior sounding. There are those who think tube amplifiers are superior sounding. There are those who think single-ended triode amplifiers are superior sounding. It goes on and on.

Subjectively, the door is left somewhat wide open.

Do we know of any commercial CFAs that have been reviewed by John Atkinson in the last 10 years or so? It would be good to see how many, and what was said about them.

Cheers,
Bob
 
I know exactly what you mean, I know something about impedances vs. frequency etc., but volume regulation is normally a part of a source unit.

Diamond input thanks, but no thanks. Someone said it is good for easy listening songs. :D

Oh Stop it! I think you have gone to far.

1) Stop hijacking threads for selling your amps. I have send an PM to admin the last time you did it in this thread. MiiB also noted it.
2) Show some respect for other peoples work. I do not think you have purchased an NX or SX amp!???? If not, you cannot comment on such a thing you have not heard yet.
3) It is not as black and white as you lay it out. If the input impedance is to low, it means that every fluctuation will have an great impact on the previous stage. So if you needs to put extra parts in the previous stage to compensate for the missing frontend in the "DIAMOND" stage, then the total system is not better.
Customers would in many cases choose an passive preamp, an valve preamp, an NFB preamp or buffer... In those cases the input impedance means a lot.
4) Should we discuss "Gryphon" as well?
5) "Simple" music with strings, pianos trompets are very demanding.

- Sonny
 
Oh Stop it! I think you have gone to far.

1) Stop hijacking threads for selling your amps. I have send an PM to admin the last time you did it in this thread. MiiB also noted it.
2) Show some respect for other peoples work. I do not think you have purchased an NX or SX amp!???? If not, you cannot comment on such a thing you have not heard yet.
3) It is not as black and white as you lay it out. If the input impedance is to low, it means that every fluctuation will have an great impact on the previous stage. So if you needs to put extra parts in the previous stage to compensate for the missing frontend in the "DIAMOND" stage, then the total system is not better.
Customers would in many cases choose an passive preamp, an valve preamp, an NFB preamp or buffer... In those cases the input impedance means a lot.
4) Should we discuss "Gryphon" as well?
5) "Simple" music with strings, pianos trompets are very demanding.

- Sonny

Hi Sonny

Every point - not true:
1. participating in this thread because the topic is interesting
2. read the NX thread, that is the opinion from forum member there, not mine
3. so we are using preamps with buffers on the output, very very low Zout
4. anytime, since that was not mine project, I participated internal parts
5. of course they are

Best regards, L.C.
 
Oh Stop it! I think you have gone to far.

1) Stop hijacking threads for selling your amps. I have send an PM to admin the last time you did it in this thread. MiiB also noted it.

Seconded, I can't understand why owners of a business section on this site are allowed to promote their products in the non-commercial sections, I have posted about this several times in the last months.

I wouldn't mind if any serious technical contribution would be provided, or if the product(s) would have any outstanding performances. Unfortunately, it's a big NO on both counts.
 
Not all are using preamps with buffers, and while I hate to admit it Sonny's amplifier sounded better than my CFA excluding input buffer. Now the buffer was not the only difference, but in all respects his Amp was closer and more intimate than mine. Simple as that. of course my newest version will be clearly better than his.... :) or so so. Really that is the fun part of this. Things are not only in isolated numbers, but has to be a part of a physical system and thus non ideal interfacing must be taken serious.

Lazy theres a big difference in participation and promoting.
 
This is not the only thread where you (LC) have been advertising your wares. For some reason your posts just have more of that flavour than others who also have some interests of their own. But Hey - you have a nice amplifier, all the power to you, nothing wrong with that -just don't think we won't notice ;)
 
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Miib's idea of using servo FB to bias the CCS's has another "side effect" !

(below) I simplified the technique letting the servo error voltage bias
the "center point" of the 2 opposing CCS's.


The unexpected thing was another 10db of LF PSRR reduction. This "bombed out"
simple little thing can even beat some of my VFA's (PSRR) now !
---- seems devoid of "bad habits" .. :D
I like this one better than my first one .. actually. :cool:
PS- I have an "opposing" VFA (9 semi's) push pull VAS , CCS, single LTP ..
120+ V/us - same 53db OLG /20-30PPM (symasym like).

OS

yes, :cool::) this is one of many good ideas I have seen in circuits that do not affect the amp performance while doing its job. The Japanese consumer companies/mfr have also some great servo circuits. They always seem to be there first. But, then they spend thier days making audio/video equipment.

Really happy some of you guys took up the challenge to do servo's control mo' bettah via CCS's. Nothing like taking a concept and successfully realizing it thru design. The exposure will produce more new ideas for servo control in VFA and CFA and CPP amps.


Although it is great to drill down to near sub-atomic levels on this CFA concept, sometimes you can simplify and get just as good results. What can we do to simplify these very sophisicated CFA designs while giving up the least performance?


THx-RNMarsh
 
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yes, :cool::) this is one of many good ideas I have seen in circuits that do not affect the amp performance while doing its job. The Japanese consumer companies/mfr have also some great servo circuits. They always seem to be there first. But, then they spend thier days making audio/video equipment.

Really happy some of you guys took up the challenge to do servo's control mo' bettah via CCS's. Nothing like taking a concept and successfully realizing it thru design. The exposure will produce more new ideas for servo control in VFA and CFA and CPP amps.


Although it is great to drill down to near sub-atomic levels on this CFA concept, sometimes you can simplify and get just as good results. What can we do to simplify these very sophisicated CFA designs while giving up the least performance?


THx-RNMarsh

I think this is the way ... miib told me I should also mirror the sources to
gain more high-Z .... too complicated (diminishing returns).
He also suggested a 3rd- order filter for the servo. Dang ! I found a filter
from heaven (below 1). In according with "KISS" (keep it stupid simple) ,
I am at 1 IC and 8 little passives.

What I have is a "cliff -like filter" ( 60db/decade) and good gain below 5Hz
to decimate any DC.

As far as the Japanese ... I looked at all my service manuals from 1982 to
present (300+) .... they all just use simple integrator' s with 6-12db/decade filtering.
I simulated them as well! :D

NO match ...
They are economically motivated .
OS
 

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Not the integrator, look at the CCS driving it, by floating the CCS you have the option of gluing them together with the input pair to gain thermal tracking. And a phono-stages with 85 dB gain at low frequencies are a lot more prone to thermal issues than a P-amp with low or NO DC gain.

That is why I stated "overkill" - we also don't need 4 pair parallel input stage
semi's either. :rolleyes:

The real world scenario with the 2Q CCS , at least on my badger with LTP/2Q
... cold day to the hottest day , .2 - .3ma more on the hot side. all runs the
same 1.6ma (.1ma per tail increase badger 2Q).
This (might ) increase VAS Ic by .2ma - OPS bias then will increase ... but depending one the Vbe coefficient this will likely be negated (at least on the
blameless).

Do we need an Arctic to Sahara amp ??

os
 
Simple circuits are good with good housekeeping. Taking out the negative influence of the servo is major. Now if you run a lateral output without VBE, thermal issues in the input stage is enough to make it run away. With your output-triple and dual VBE you control it elsewhere. sorry to derail this not my intention of turning it into a housekeeping subject.