Like this, both DC and AC are balanced. (source having the same impedance than the output one of the IC) at the price of ~0.4dB losses ;-)
That is avoided for CFAs (witch have, indeed, CM rejection as a drawback ;-)
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Really, you don't understand? There is a whole business built around these small differences and controversies on every imaginable level. The beauty of the law of diminishing returns means that if you have evidence of a small difference that audiophiles decide is an improvement you can up the price considerably.
This article doesn't appear to have any serious intentions regards discovering common psychoacoustic mechanisms that could actually improve listener's experience of sound reproduction in their homes.
A small detail --- even if the CMR was infinitely great, the pracical CMR is also determined by the source and cable balance. It inst possible to expect better than 1-2% winding symmetry in manufacturing bal cable. Its just mechanically is not able to make such cable to a high enough balance precision to be better than 1% or -40dB CMR.
Of course a 1-2% source Z unbal is added to that.
So these really high "out of system" stand-alone CM tests are pretty far from what we are exposed to in the real world.
Am I right or wrong about this?
THx-RNMarsh
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Oh, yes, I think (but who can be sure) I understand. Just I am not at all in concern with this (very small) business.
If somebody spend a fortune to buy esoteric speaker's cables, it is the proof that he can afford them. (I don't). And he is not totally fooled. As he was not fooled buying a Bugatti. He is persuaded that he owns the best cables money can buy, and can impress his friends talking about them.
And, what is best ? If you build a recording studio that you intend to rent to free lance engineers, what is the mixing desk you gonna choose ? The one you think is the best at this time, or the one that is hype ?
(Same question for the car of a taxi driver)
Now, if it is for you, you will make an opposite choice, and, anyway, nothing will never prove what you consider as best is really best. See what I mean.
Now, about this thread, it is mostly frequented by people who have some notions of electronics, including some big names like SYN08. When there are discussions about designs, it is interesting and informative. When is is about personal feelings (Listenings) it can be, as when somebody point his finger to something. After that, it is you who see or not. No need to fight endlessly about color's preferences and attacking people that do not share our personal tastes.
As we know very little about psycho acoustic, and we are not even sure all individual share the same, talking endlessly about this or audiophile fooleries that no one of us is supposed to be the victim is, in my opinion, like a middle-age witch hunt. Unworthy of the serious that those who claim to speak in the name of science should maintain.
I can only see what they are pointing at if I have an opportunity to listen too, as far as I'm aware that happens very little on this forum, Pavel's offerings being a notable exception.
How do you know we know very little about psychoacoustics? Is it not the study of human perception, has not this perception evolved i.e. it's about survival and the mechanisms are common to our species? Probably other species too and there are studies into the perceptions of other creatures, and there seems also to be commonalities.
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The musical side had evolved during human history and had been perfected and codified two centuries ago. The reproduction of the recorded sound has one century of history.
Entertaining read... my take on all that (and what went b4, back to the JLH days at Stereopile, or even Julian Hirsch, et. als. at various rags in the '70's and '80's) is the immediate Arny Krueger ABX, DBT, etc. vs. sighted long term argument is comparing apples to oranges.
IMO, both can be justifiable positions / conclusions. Immediate double blind results simply reflect the accuracy and precision when measuring & monitoring the results using, essentially, the same philosophy and design instruments that were used to produce the product / device under test.
Whereas, long term, slow listening under sighted conditions reflects the training and enjoyment under a presumed set of listening conditions; e.g., use of DSP with or w/o multiple speakers to provide the illusion of a studio mix, or concert hall, etc. As such, these results often contain complex factor interactions that are hard to account for if one makes a statistical evaluation of data generated to support a given perception.
Perception as the critical variable, is probably the key word here, vs. actual measurement confirming a designed set of data with specific criteria under statistical control
Two different beasts
Dear T-E, this is called "experience", "guessing" is reserved for those electronics illiterate chaps, self appointed competent "audio designers".
Case in point, 10 years ago I designed a mosfet amplifier (with the now defunct 2SK1530/2SJ162) not with 3MHz ULGF like Dadod, but with 8MHz ULGF (two pole compensation), simply "because I could" and I was curious how much could I push it. I took all the imaginable precautions and built it like a RF piece of gear (that it really was, at that frequency), photo is attached. And yes, it is a CFA, with some twists to improve noise, PSRR and CMRR.
Initially I was very happy with the results; after moving out the output coil off the board distortions at 300W/4ohm @20KHz were under 5ppm (0.0005%), loop gain simulation and measurements were showing a healthy 60 degrees phase margin, sounded perfect to my ears (and a few friends). I was about to declare a major breakthrough, until I had the idea to do a load scan at full power. It took me not longer than a week to find several combinations of real speakers or synthetic reactive loads that showed this amplifier is very sensitive to various reactive load parameters. And even if initially it never destructively bursted into oscillations, it was easy to measure and hear the effect of transient burst oscillations at the output. Lowering the ULGF to 4MHz increased the phase margin to 80 degrees, but the transient stability remained shaky at best. I ended up blowing one channel during capacitive load testing (and no, contrary to what people think a 1uF capacitive load is NOT the worst case for loading an audio amplifier, 1-50nF is where the devil kicks in) and kept the other channel in my museum of failed projects. And never published this project for anybody else to try.
Lesson learned - Bode was right. Given an amplifier and a frequency compensation order (two in this case) you cannot push the HF loop gain without compromising, one way or another, the stability margins. I knew this all along from feedback theory, but what I grossly underestimated is the garden variety of possible loads (speakers+cables) that a power amplifier may encounter. So I concluded that there is a good reason why commercial amplifiers are barely going over 1MHz ULGF and almost always use Miller compensation (not even standard TPC). Those designers knew the risks before I discovered them on my time and dime.
You don't want to hear about more adventures with audio power amplifiers using pole-zero cancellation techniques, able to push the ULGF up to 20MHz even with power bipolars with Ft=30MHz, and since the OLGF is theoretically set very high by the input stage pole(s) they don't suffer by the Bode stability limitations as above, where it is the output stage enforcing the open loop frequency response; in this case, it was the circuit sensitivity (to power supply voltage, temperature, load, etc...) that killed the project, something that trivial simulations will never show (unless Monte Carlo simulations are used).
And Dadod is wondering why I am so "conservative" in ULGF... and I'm not even an "audio designer" 😀.
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syn08,
I cannot disagree with anything you are saying, usually wide bandwidth (without proper compensation) leads to a lot of heartache.😀
A problem with some audio designers is that they get hung up in their belief systems and usually paint themselves into a corner. Case in point being the no-feedback crowd. 😉
Have you posted the schematic or are you willing to share if possible.
Jam
PS. Great idea to have local bypassing of the output devices.
I cannot disagree with anything you are saying, usually wide bandwidth (without proper compensation) leads to a lot of heartache.😀
A problem with some audio designers is that they get hung up in their belief systems and usually paint themselves into a corner. Case in point being the no-feedback crowd. 😉
Have you posted the schematic or are you willing to share if possible.
Jam
PS. Great idea to have local bypassing of the output devices.
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John Curl's Blowtorch preamplifier part III
Third circuit is *not* unity gain at DC. This is the one that I cannot reconcile with:
John Curl's Blowtorch preamplifier part III
Admittedly my brain isn't firing on all cylinders (writing a paper closer to what Auplater does) but are we seeing an oops from LTSpice wrt convergence at DC?
>Edit: wrong links fixed
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First, thank you (seriously) for sharing it. (Please, be nice, remove this strange letter when you quote me: my initials are T.T.)
Okay, I read you carefully and cannot contradict you. I also looked at your printed board and, indeed, it seems conform to what you said about it about RF precautions.
Let me just ask you a question. According to your words, you have therefore designed and produced a CFA with remarkable performance . Subjected it to intensive testing, which is professional and all to your credit. You had realized that this amp was limit in terms of stability. Very well. I miss the end of the story. I imagine that you have corrected your amp, on the bench, to obtain a more "solid" compromise in your eyes ?
This is what I would do for an industrial product.
Now, if it's for your personal use, you control your loads, don't you ? So you can afford to find a more sporty compromise in your living room, right ?
About the Richard's Amp. What the hell ? It is not the first or last time an amp is burned on the bench. Right ? If I understand well, he was not here when this happened.
Nothing prevents us from supposing that one of his collaborators left dropping a screwdriver in the amp and avoided saying it. As Richard is well equipped with measuring instruments and obviously knows how to use them, I am sure that he will look into the matter as soon as he can take care of it and will make Dadod known from his "experience" for the greater benefit of both parties. Right ?
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You are the king of Presumption. Even when we try to stretch out our hand, you have to bite it ?
(Do you give your human qualities a score as high as that which you think of your competence in audio design?)
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.Controversial and offensive to make believe high-end audio businessmen?
You forgot to finish the sentence with "to you", as shown below.
I am no "audio designer", lesser a "competent" one, and applied electronics is not (actually never was) in my professional life scope (did a few analog IC designs after graduating, though). I am indeed intolerant when it comes to charlatans, snake oil merchants, dishonest idiots, by-the-ear audio designers, and pathological/delusional liars, so yes, in this respect my "human qualities" are lacking.
Ignorance and/or lack of education is is not a sin in my book, cheeky ignorance is. Go figure.
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