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Message Re: Apport de la sortie Balanced/Symétrique 29 Juin 2018 10:34

burndav a écrit:L'erreur consiste à effectuer une généralisation empirique, qu'elle soit effectuée dans un sens ("le symétrique, c'est mieux") ou dans l'autre ("le symétrique, ça n'apporte rien").

Si on relit le topic c'est bien mon propos et le message que je voulais passer, dans mon cas principalement suite aux conclusions hâtives suites à des comptes rendus d'écoutes ponctuels et personnels. Mais tu as raison de préciser que c'est aussi vrai pour les données techniques et les mesures.

burndav a écrit:Et quoi qu'il en soit, quand bien même cela serait vrai, je continue à dire que cela ne permet pas d'en conclure quoi que ce soit sur la différence existant entre les sorties asym. et sym d'un même appareil : il y a nécessairement des différences (rien que l'impédance de sortie...), mais elles seront de plus ou moins grande importance d'un appareil à l'autre (c'est ce qui remonte des retours effectués ici, et c'est d'ailleurs un peu la source du désaccord initial).


Différences veut-il dire forcément amélioration de tous les critères audiophiles ? Ce point là me dérange, à titre personnel, et m'amène à penser aux effets psychoacoustiques et Placebo. (Juste mon opinion sur ce point et chacun la sienne...).

Message 29 Juin 2018 10:52

Ben pour l'exemple donné, doubler l'impédance de sortie divise le facteur d'amortissement par deux, donc l'impact dépendra également du transducteur connecté... partant de là, non, c'est pas forcément positif, mais ça je crois que c'est un consensus général.
Après, les modifications (slew rate, puissance, impédance, THD, SNR...) étant de toute manière relatives, même si les choix sont similaires, les impacts seront différents (exemple bête : je double l'impédance de 0,25 à 0,5 ohms -> pas grave. Je passe de 4 à 8 -> aïe).

Message 30 Juin 2018 03:41

De ce que j'ai lu, sur des casques à grosse impédance (cf hd800/k1000) le symétrique apporte un bon plus.

J'avais mis une fois mon HD650 en symétrique sur un ampli DIY B22 et j'avais comparé sur un asymetrique, j'ai pas remarqué de grandes différences, j'avais fais le comparatif rapidement.

Apres de ce que j'ai entendu sur Stax avec les SR-007 (mkI et mkII), SR-009, SR-507
Mon DAC DIY Buffalo3 se: la sortie asymétrique est piqué sur le point chaud et le ground de la sortie symétrique et la meme chose pour mon ampli casque (un 727II modifié). En gros le RCA est un demi-XLR sur mon setup
Le XLR change de façon audible le rendu sonore (surtout sur le 007): plus sec et controlé, apres les stax sont symetrique dans le fonctionnement meme des drivers. Je pense que c'est un cas particulier.

Message 30 Juin 2018 07:20

kookaburra a écrit:Différences veut-il dire forcément amélioration de tous les critères audiophiles ? Ce point là me dérange, à titre personnel, et m'amène à penser aux effets psychoacoustiques et Placebo. (Juste mon opinion sur ce point et chacun la sienne...).

Et je rajouterais même : Cette différence sera t'elle nécessairement perceptible par ce récepteur, somme toute, très approximatif, qu'est notre cerveau ? (enfin surtout le miens pour le côté approximatif  :lool: )

Message 09 Juil 2018 09:52

AUDIO MYTH - BALANCED HEADPHONE AMPLIFIERS ARE BETTER https://benchmarkmedia.com/blogs/applic ... are-better

THIS MYTH GOES SOMETHING LIKE THIS:

"Balanced headphone amplifiers are better."

"If balanced line-level connections work well, balanced headphone outputs should also work well."

We disagree!

Benchmark does not offer balanced headphone outputs on any of its products. The reason for this is that a voltage-balanced interface serves no useful purpose when driving headphones. The truth is that a conventional single-ended headphone drive is technically superior to a balanced drive. This paper explains why single-ended headphone amplifiers are inherently more transparent than balanced headphone amplifiers.

Please understand that Benchmark strongly encourages the use of balanced line-level interfaces between audio products. All of our products are equipped with fully-balanced XLR analog inputs and outputs. In these box-to-box line-level connections, a balanced interface can provide substantial performance improvements. Balanced line-level interfaces reject hum and noise while providing a higher voltage level. The higher signal levels can improve the SNR (signal to noise ratio) of the audio system.

If balanced connections work so well between audio boxes, it seems reasonable to expect improvements when driving headphones with a voltage-balanced feed. This expectation provides a marketing opportunity for any audio manufacturer that is willing to exploit customer expectations. Many are willing, and this is how audio myths are born and nurtured. Benchmark does not promote these myths nor does it embrace trends that do not contribute to transparent sound.

This expectation that balanced headphone amplifiers should be superior to single-ended amplifiers, ignores some of the most basic laws of electricity. The current into and out of a two-wire network is always equal and opposite. This means that the two-wire transducers used in headphones always see fully-balanced current. It also means that the headphone drivers are completely ignorant of the difference between single-ended and balanced-drive voltages.

Let me spell this out again: Headphone transducers are balanced devices. They have two wires. The electrons that flow into one wire must flow out of the other. The current is always balanced. The headphone transducers cannot detect the difference between a single-ended drive and a voltage-balanced drive. The system is balanced with either type of voltage drive.

But, this does not mean that balanced and unbalanced headphone amplifiers will sound the same! In many cases, voltage-balanced headphone amplifiers will produce more noise and more distortion than single-ended amplifiers of an identical design. The reason for this is that two separate output amplifiers are required in a voltage-balanced amplifier, and each must drive one half of the transducer's load impedance. The output noise will double because there are two amplifiers instead of one. The damping factor will degrade by a factor of 2 because both amplifiers contribute to the source impedance of the balanced amplifier (output impedance is doubled). Distortion will usually increase because each amplifier is required to drive half of the impedance that would be seen by an unbalanced amplifier. Power consumption will increase by a factor of 4 for a given output level (assuming the power supply voltage rails remain unchanged).

In fairness to balanced designs, I should point out that a balanced output can deliver 4 times the power for a given power supply voltage. However, this would only be necessary if the product was battery operated. The balanced output would offer no real advantage in an AC powered amplifier.

Please note that distortion is not always a bad thing (see Two Distinct Types of Audio Products). Many audio products are designed to add some harmonic distortion in an effort to add warmth to the audio reproduction. This is an artistic choice that will change the way a recording sounds. If the goal is to add distortion, a balanced headphone amplifier may produce more harmonics than a single-ended design.

In contrast, Benchmark products are designed for maximum transparency. Our goal is to build products that faithfully capture and reproduce music. This means that our products are not designed to alter the sound of a recording. This transparency is critical in a studio monitoring chain. We feel that this also makes our products well-suited for home playback when a listener wants to hear the music the way it was heard in the studio. A voltage-balanced headphone amplifier would run contrary to our goals.


et aussi :

"Single ended driving"      versus      "balanced driving"      versus      "active balanced ground driving"
http://www.meier-audio.homepage.t-online.de/grounds.htm

The classic implementation of a headphone connection is that of "single ended driving". However, over the past few years other implentations have been developed that have major advantages in improving soundquality. In this chapter these implementations are compared on a technical basis.
"Single ended driving"
Each driver of a headphone is connected to the amplifier by two wires. One of these wires (the ground wire) is directly connected to ground and thus carries a constant zero-Volts signal. The other wire is connected to the active part of an output stage and carries a varying voltage, the electrical audio signal. The driver is driven by the voltage-difference between both wires.
The voltages of the two active wires change continuously and the external electrical fields generated by the electrical charges on the wires change accordingly. There is energy associated with these fields and thus energy is constantly stored and released. The dielectric properties of the insulating material have a strong influence on this process and thus effect sound quality.

"Balanced driving"
With a balanced setup the wires of each driver are both connected to an active output stage. Both wires carry the same signal but on the "ground" wire the signal is reversed in sign. The amplitude of each signal is half that of the signal in a single ended setup. The driver is driven by the voltage difference between both wires and is the same as in a single ended setup.
As the voltage signals on both wires are reversed in sign, so are the electrical charges on these wires. The total electrical charge thus becomes zero. The external potential field is strongly reduced and much less energy is stored and released when an audio signal is applied. The purity of the sound signal is much less effected by the properties of the insulating material.
Principally a balanced setup therefore does have a clear technical advantage over a single ended setup. However, there also is a major practical drawback. The "ground" wires of the two drivers of most headphone are electrically connected to each other and thereby are forced to carry the same signal. This is not allowed in a balanced setup and therefore such a setup requires recabling of every headphone that is to be used.

"Active balanced ground driving"
With "active balanced ground driving" the ground wires are still connected but these wires are not kept fixed at Zero-Volts potential. An extra signalcomponent is added to all the four wires (both wires for both drivers) such that the sum of the voltages of the 4 wires is constantly zero. This extra signalcomponent is the same for all wires so the voltage differences between the two wires of each single driver do not change when compared to a single ended or balanced setup. The effective audio signal is still the same.
However, since the sum of the voltages is zero, the total electrical charge on the wires is also zero, like in a balanced setup. Again, the external potential field is strongly reduced and much less energy is stored and released when an audio signal is applied. The dielectric properties of the insulating material have much less effect on the quality of the sound signal.
The concept of "active balanced ground driving" thus offers the same advantages as "balanced driving". However, no costly recabling of any headphone is required.At the left picture below we see the signals as generated by a conventional headphone amplifier. The ground signal is kept constant. Left and right channel signals vary independently.

The middle picture shows the four signals involved in a balanced setup. The two signals for each driver are the same but have opposite sign.

At the right we can see the signals generated by an "active balanced ground" setup. The ground wire now carries a signal that is also added to the left and right channel signals. The difference between Left and Ground and between Right and Ground is the same as in the other two setups.The left picture below shows the electrical potential field of the positively charged headphone cable when both signal wires carry a positive signal at the point of time indicated by the yellow bar at the left picture above.
The right picture shows the potential field for balanced driving and for active balanced ground operation. It can be easily seen that field potentials are much lower than at the left picture.The differences are even more pronounced in the far field, as shown in the next pictures. Since the "balanced" headphone cable has zero netto charge there is hardly any energy stored in the far field.Apart from these principle benefits there are also other technical advantages offered by both balanced concepts.

When a positive signal is applied to a headphone driver of a single ended headphone amplifier current passes from the output stage of the amp, through the headphone driver towards the ground plane of the amp. During this process the current is "taken" from the positive power supply line whose voltage, as a result, will not be entirely constant. (In the pictures below the positive and negative supply lines are depicted as two large storage capacitors.)

The currents that run through the ground plane do induce small voltage differences. Ground is thus polluted and since it acts as a internal reference for all signal amplification processes sound quality is impaired.

Also variations of the powersupply lines are not entirely rejected/neglected by the output stage and are partly transferred to the output signal. This reduces sound quality even further.

When a signal is applied to a "balanced" or "active balanced ground" setup current passes the signal output stage, the driver, and the "ground" output stage. Both positive and negative powersupply lines are "loaded" simultaneously. No driving currents pass through the internal ground plane. There is no pollution of the internal referfence.

The voltage variations of the two powerlines are mirrored. Their mean value is roughly constant. This strongly increases their rejection at the output stages.If voltage variations are found in one of the powerlines only, then these have a similar effect on the signals of both the signal output stage and of the ground output stage. However, it is the difference between the two output signals that drives the headphone. This difference is not changed and the effective audio signal is not influenced. PSRR (Power Supply Rejection Ratio) is very high."Balanced driving" and "active balanced ground driving" thus offer many advantages for a faithfull reproduction of your favourite music.

"Active balanced ground driving" has the advantage over "balanced driving" that no expensive recabling of the headphone is required.


Vous en pensez quoi de tout ça ?  :-?

Message 10 Juil 2018 00:48

Je pense que l'explication de Benchmark est totalement alambiqué et que c'est juste une justification sans fondement sur pourquoi "eux" n'ont pas de balanced en sortie casque. Du marketing inversé en somme.


Ce que raconte Meier est plus convaincant, cohérent et me semble plus en phase avec ce que j'ai appris dans mes cours.

Message 10 Juil 2018 08:18

J'ai conclu pareil... Quand même les "pros" t'embrouillent" avec du marketing comme explication légitime - dans un sens ou dans l'autre * - la lutte contre les mythes audiophiles devient vraiment très compliqué !  8-)

* on l'a vu aussi dans l'autre sens avec Sony sur le rodage sur son baladeur flagship : la différence entre le marketing sur le site et les explications en Off des ingénieurs... ça ne va pas aider à arrêter le mythe du rodage. :-.
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