CFA Topology Audio Amplifiers

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#1,381
Waly said:
Shunt compensated CFAs excel at all these attributes, they simply can't be beaten by any other topology.
Click to expand...

As Peter Baxandall observed, shunt compensated amplifiers are "suboptimal in all respects". The shunt compensation capacitor simply increases the non-linearity of the stage to which it is connected.

P.S. Waly, I've just seen your email...😀
 
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#1,382
Waly said:
- Clarity
Clarity is the prime acoustical goal because its perfection depends on the successful attainment of all other goals. Of paramount importance is dialogue intelligibility in movies, but one must be able to understand musical lyrics, detect quiet background details, and distinguish the timbre of each instrument. Elements that affect this goal are varied including equipment quality, room decay times levels, ambient noise levels, early reflections and room modes.

- Focus
The ability to precisely locate each reproduced sonic cue or image in a three-dimensional space is defined as acoustical focus. Recordings contain many such images superimposed side to side (2 channel music) and front to back (multichannel music & movies) in every direction for 360 degrees around the listener. A system is said to have pin-point focus if, from the perspective of the listener, each of these images is properly sized, precisely located, and not wandering. Good focus also provides that individual images be easily distinguishable from amongst others within the limits of the recordings quality.

- Envelopment
An audio system should reproduce virtual images of each recorded sound presenting the listener with its apparent source location in a three-dimensional space. Each sonic image relates a part of the recorded event and together these sounds compose a wrap- around soundstage that envelopes the listener. Proper envelopment requires that the soundstage be seamless left to right (2 channel music) and front to back (multichannel music & movies) without interruption by holes or hot spots caused by speaker level imbalance or poor placement.

- Dynamics
Dynamics is simply defined as the difference between the softest and loudest sounds reproducible by a sound system. While much emphasis is placed on the loudness side, it can be shown that the audibility of the softest sounds is an equal measure of system performance. If low level signals are overwhelmed by excessive ambient noise or reverberation in a room, they will not be audible due to masking effects and will impact focus, envelopment and clarity. At a minimum, a system must be capable of reproducing loud passages with ease and without excess while soft sounds remain easily audible.

- Response
The frequency response of a system is a measurement of the relative levels of all reproduced audio frequencies. The smoothness of response can be observed in a variety of ways; as improper tonal balance including boomy bass, excessive treble, improper musical timbre, or a general lack of realism. Factors of importance include selection of high quality components, and proper system set-up including (in a small room) proper listener position, speaker position, and correct use of equalization. At a minimum, the system must be non-fatiguing all sound levels, articulate and faithful to the original signal.

Shunt compensated CFAs excel at all these attributes, they simply can't be beaten by any other topology.
Click to expand...

You could say that in much less words, to be copy of the live music.

But tell me what technical requirements an amp should fulfill to produce that sound?
There is not easy answer to that in my opinion.
 
#1,383
You do not have to use shunt comp in a CFA.

In fact, other than one specific type, it looks like most of the types we have applied to VFA over the last few years on this forum are perfectly applicable to CFA.

And, certainly shunt comp is a bad thing for VFA . . . but this is not VFA, so it may be that trading a bit of distortion using shunt comp is a worthwhile tradeoff for the simplicity, bandwidth and slew rates you get with a CFA.
 
#1,384
@dadod, the rest

Exact reproduction of the source. All of the attributes are supposedly encoded in the source material, the amp shouldn't modify it. Also each channel needs to be perfectly time-aligned in order to accurately reproduce effects that are dependant on delays between recording channels. Other than that, I don't know.
 
#1,386
dadod said:
You could say that in much less words, to be copy of the live music.

But tell me what technical requirements an amp should fulfill to produce that sound?
There is not easy answer to that in my opinion.
Click to expand...

Ahem, isn't it why some of use favor most amps within this CFA topology? May be it is not the topology (that counts) but what can (easily) be achieved with it.

Remember how imperfect the speakers are, especially if we talk about the crossover of multi-way systems. So an amp should be able to coup with so many non-ideal situations (sometimes I wonder why it seems that amp designers do not realize that speakers are never be a part of their design, or they think that resistive load is all there is :scratch1:)

From many VFA amps I have simulated, my CFA is superior in "all important" aspects except for:

1. Distortion, which is not critical soundwise.
2. Noise floor, which I think seriously degrade the performance of the bass/LF.
3. "Transconductance", which is of course not as good as bipolars but may be if the experts know what I'm talking about, they may be able to improve it. But this has been the flaw of mosfet amp designs for many decades.
 
#1,392
I still cannot understand why some have such an allergy to CFA that they try to rot this thread by all the manners they can imagine.

Notice it is obvious they never have even listened to any CFA. Or build any.

There are several schools, in audio design. Objectivists, who believe numbers tell all of an equipment, even those you read in a cartoon (simulations). Subjectivists, who imagine that schematics are recipes, and each component has to be tasted, with their court of snake oil vendors...

As habit, the best way is in the middle. We measure continuous signals, we listen transients. Across imperfect speakers. Measurements, like distortion numbers, are a good way to insure our designs fulfill a minimum requirement, and if any change goes in the good direction. But we would have to know exactly what is the meaning of each number, and we don't know: What is the distortion number under-it we don't notice any harmonic distortion ? We have to take care of each component, because they are not perfect, means they do have a character. In some places, like feedback, we do care to the quality of resistances.

The good way is to try to get the best numbers ... listening to any change to see if it brings a real improvement in listening experience. (Yes, can have best numbers, but poor musical reproduction). Find the best devices for each purpose. The best compromise in schematics between simplicity and performance.
That cannot be done when we design inside simulators.
That is the real problem with this kind of study in forums (that and the trolls).

Yes, there is a difference in listening experience between VFA and CFA. In the reproduction character, mainly in transients reproduction. Sorry, but it is true. Many time verified by many.
Some of us tend to prefer this character ? What the hell ?

Some really believe "CFA are not good for audio." ?
Perfect: Don't even try and go build any other amp you want. But, please, let-us work in peace.
Who, between this thread contributors are trolling in all VFA threads, claiming endlessly 'VFA is not good for audio" ? Who is bad educated and boring?

Yes some of us are "old farts from Jurassic", eq with REAL experience. Is-it worse than to be unwashed students or half blind who believe books are bibles and use complicated words, to manipulate uncorrelated concepts (shunt comp blabla) they don't understand ? Things are really so simple, in reality: phases, levels, currents, feedback, gain. All correlated. And poor components.
There is no religion in electronic, sometime you better accelerate to avoid a car accident.

My visitors are usually impressed by what they ear when we listen music at home. I have 3 amplifiers, i use the one i prefer for each purpose. Class D for my sub, VFA for the bass-medium, CFA for the medium-trebles.The ones witch reproduce some music i have produced as a sound engineer the closest to what i tried to achieve in the recording studio. And i try to learn more to improve it further. In an humble manner, because it is far to be perfect.

No religion. (Too long post, sorry)
 
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#1,393
Thank you Esperado :wave:

I will repeat the pertinent part "Please let us work in Peace"

I have built a few amps, I started with Dr. Leach's Low Tim.

Chocolate is my favorite, but there is Vanilla and Strawberry for those that do not like Chocolate, I hope you enjoy your own favorite, but stop nit picking my choices.

Thanks
 
#1,398

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#1,399
Esperado said:
...our ears to decide, because... we listen music with our ears.

At the end, how can-we be sure...
Click to expand...

Well, the usual way to deal with this to follow well established practice.
Unbiased tests, checks for repeatability, statistical analysis.
All the standard procedures that are the absolute minimum in any real science.

So what is your test protocol, sample size, confidence interval?

Best wishes
David
 
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#1,400
wahab said:
Theses are not correctly done, Dadod , it s what is at the left
of the fundamental frequencies that interest us , you should
set the simulation time to 10ms at least and the step to 100ns
and then zoom the 0+ Hz-25KHz zone in the graph.

For Manso s original schematic and with a linear x axys it looks like this :
Click to expand...

OK this is what I've got for high LG, and 1kHz is 157db below 19+20kHz signals.
 

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  • CFA-100W-highLG-CCIF-IM-b.jpg
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