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Review and Measurements of Ayre CODEX DAC & Amp

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#81
As I said:
It is possible to design amplifier circuit with low distortion without using negative feedback, just not that easy....

Ayre need to rework their design, no negative feedback by itself is not a bad thing.
You can get far with a lots of feedback, just be aware that your typical audio opamp get less feedback as frequency goes up....
 

FrantzM

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#82
Hi

Crappy engineering shouldn't cost more than adequate engineering. Let's not try to justify a pitiful product. This Ayre thing is $1750.00. Its redeeming value is non existent. There are too many ways to distort a signal that won't cost as much. There is a market for such BS I don't thing we are that market.
 

gvl

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#83
I have a pair of "DUAL SUPER NON-NFB CIRCUIT" Denon POA-4400 monoblocks from the 90s. Unclear which stage is exactly NON-NFB but it is proudly printed on the front panel. The specs aren't too shabby, and probably not too far from reality on a properly adjusted unit. And this is a power-amp, not a DAC.

 
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March Audio

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#84
I need to voice my opinion, although I'm biased....
Yes, there is a lot of snake oil in the Audio Business, I'm not going to pay more for my speaker cables than my speakers, 2.5mm2 stranded wires are fine. And those that believe in "audio grade" fuses, I would like to sell the eiffel tower...
But there are also things that's hard to measure, simply because there are complex things going on and audio measurements methodes aren't really that advanced, mostly using static signals. The Human ear is an amazing thing, able to hear tiny details.
And negative feedback are not a good thing, but a solution to fix not that linear and usually bandwidth limited designs. Read up on Nelson Pass's Article at https://www.passdiy.com/project/articles/audio-distortion-and-feedback, there are also other good articles there. Anybody rememeber Matti Otala and his work ?
It is possible to design amplifier circuit with low distortion without using negative feedback, just not that easy.... My dac1541 typically get 0.003% THD at full signal level without negative feedback, it just takes 50 transistors per channel, most of them to ensure that the amplifying parts operate optimally....
And btw, if I had the choice between any old Ferrari and a new fancy Japanse sportscar, I'll take the Ferrari without a second of hesitation....
Ok, that's fine in itself, but does a no feedback but less linear design actually sound better than a more linear feedback design? At what point does less linear no feedback start to sound worse?

I have only skimmed the Pass article but one comment stuck out like sore thumb.

Given the complaints of audiophiles over the sound of high-feedback type amplifiers,

IMO audiophiles are the absolute last people you want to listen to if you want accurate information regarding sound quality. It may be a generalisation but in my experience they rarely use any control in their assessments and as a result their conclusions are always highly suspect or entirely false. In fact its worse than that, they tend to eschew the use of any controls.

This is a genuine question, I don't know the answer, what is the evidence that a similarly linear no feedback design sounds better than a feedback design? When I say linear, I would suggest with static tests THD/IM below - 110dBfs which is not unusual these days with DACs, pre amps and some power amps.
 
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anmpr1

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#85
The Human ear is an amazing thing, able to hear tiny details... And negative feedback are not a good thing
a) the human ear is not as fine a resolving instrument as a lot of audiophiles might want to believe. In fact, the ear is like a tube...it gets worse with age. The ear is easy to fool, and is not nearly as resolving, nor does it have the fine acuity of, say, the visual sense. Vision can easily be corrected with lenses. Hearing cannot easily be corrected, at least in a natural way. It is very easy to conduct reliable and valid AB tests with vision, but quite difficult to do it for hearing (I am referring to AB testing at matched levels on music), as the latter takes time and a lot of concentration is required on the part of the participant. That said, gross tests, such as those audiologists test for (speech discrimination, speech reception thresholds, etc.) can be done rather quickly, and can show how far one's hearing deviates from a normal baseline. All reviewers who claim to hear these big differences ought to be required to take an audiology exam, and publish their results. That would only be fair. So that when they tell us about the 'delicate' highs, we can judge how far down their hearing is at those levels. LOL

b) negative feedback is not 'bad' per se. Just depends on the circuit, and what the designer is trying to do. Back in the day, Julius Futterman's amps used a lot of feedback, and they were considered exceptionally 'clean' by reviewers as diverse as Julian 'it all sounds the same to me' Hirsch, and the 'underground' reviewers, the latter who were parodied in Dick Calderhead's Audio Critic cartoons: "The high end is grainy, the upper midrange is hooded, but from 250 Hz to 400Hz, I've never heard anything more liquid." Or "The midrange has tubelike depth. The bass has that SS tightness. S/N is in a class with the best ICs. But it would probably all sound better using Audio Research's new Analog Modules."
 

bravomail

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#86
Thx for excellent review, Amir, and thx forum members for delightful discussion!
I have genuine dislike for non-technical audiophiles, cause I feel that they cannot properly interpret what they hear. Like AOC said: "Feelings are more important than facts!".
Being nontechnical you can be easily fooled by Non-Feedback design claims. You need to know why negative feedback was introduced in a first place. First amp designs did not have negative feedback. Negative feedback is the only proper way to fight physics of noisy components of an amp. You produce an amplified sound and you subtract the noise which was introduced by your transistors or lamps. It is alpha and omega of Hifi sound. To claim that nonFB design will sound better is mind boggling!
 

anmpr1

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#87
What does this imply about John Atkinson? Is he truly incompetent? Or is he a tool...
I'd say the latter. But what kind of tool is anyone's guess. I slummed over to his Website, and made it through a couple reviews. I'll say this for the man, compared some of Stereophile's writers, Atkinson is a paragon of based objectivity. One of their writers (at a hotel room hi-fi show) wrote about a loudspeaker demo: "So beautiful and warm and all-embracing..." I had to read it twice to make sure. A loudspeaker? What kind of man uses those words to describe a loudspeaker? I cringed, and clicked away. It is as if the writer was experiencing some kind of infantile regression. Back to the womb. Or something. Good grief!
 

svart-hvitt

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#88
I'd say the latter. But what kind of tool is anyone's guess. I slummed over to his Website, and made it through a couple reviews. I'll say this for the man, compared some of Stereophile's writers, Atkinson is a paragon of based objectivity. One of their writers (at a hotel room hi-fi show) wrote about a loudspeaker demo: "So beautiful and warm and all-embracing..." I had to read it twice to make sure. A loudspeaker? What kind of man uses those words to describe a loudspeaker? I cringed, and clicked away. It is as if the writer was experiencing some kind of infantile regression. Back to the womb. Or something. Good grief!
If you compare x to something ridiculous y, what is the value of a relative comparison, say x vs. y? What happens to the standard if you use y as a reference?

In some restaurants they have €10.000 wines and €100 per kilogram lobster. This stocking of expensive goods may not be due to the restaurant owner expecting high sales of said items, but to make the rest of his menu appear relatively luxurious at a reasonable price (it has at least one name: anchoring).


Atomicbob, John Atkinson, and many more. Valuable for the merchants. A science oriented audiophile should set his standards irrespective of the environment in which a reviewer makes his business.
 

restorer-john

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#89
I have a pair of "DUAL SUPER NON-NFB CIRCUIT" Denon POA-4400 monoblocks from the 90s. Unclear which stage is exactly NON-NFB but it is proudly printed on the front panel. The specs aren't too shabby, and probably not too far from reality on a properly adjusted unit. And this is a power-amp, not a DAC.
They likely use the same feedforward/direct distortion cancelling system as used on many of their previous non-NFB products like my POA-1500s. It reduces static distortion to levels so low I can't reliably measure it a high powers.

Trouble is, this is THE amplifier (POA-1500) that has eluded my efforts to track down the source of transient induced instability. When it was new, it vaporized the lead-in wire on two very expensive tweeters on a benign medium/high sax transient- the same piece on other amplifiers at same/higher levels on the same speakers caused no such issues (yes, I had spare tweeters on hand).

After discussions with Denon Japan's engineers in the early 90s, and various experiments, I gave up. I bought another one just for fun and the performance was identical. Excellent on the bench, but could be stimulated into bursts of oscillation at certain powers and levels in the real world using music. (Almost like VW's cheating scandal...)

Interestingly enough, it was the first high power amplifier of excellent pedigree and beautiful design that made me seriously question whether measured performance was everything. I keep it (and its spare) as a reminder of that. And, because its matching preamplifier is my favourite preamplifier.

My POA-1500s have a similar spec sheet:

1555362985464.png


block diagram of POA-1500

1555363105282.png


POA-1500 power stage (talk about complex...):

1555363183307.png


PAO-1500 voltage stage:

1555363243069.png


Your POA-4400 uses a similar design in some ways, although not identical and IMO couldn't really be classed as pure non-NFB:

POA-4400 power stage:

1555363767619.png


POA-4400 voltage stage:

1555363816512.png
 
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gvl

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#90
I suspected the NON-NFB in this case had to do more with marketing than actual implementation. I never experienced instability but with 98db sensitive speakers I'm probably too far from the danger zone.
 

Jimster480

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#91
Wow what another FLOP. I saw this unit being talked about during my time @ HeadFi and people were swearing by this brand left and right. Saying that they make super high quality products that have performance bar-none.
Instead its basically beaten down by $75 chinese DAC's? It seems that the name of TOPPING should mean something in Audio because it seems that they are delivering while other companies are doing the opposite...
On forums like HeadFi; many people will talk down to Topping users or talk bad about Topping products while praising products like this one... sad to see that its actually the Topping owners who would be in the right to talk bad about these products.
 
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