EC Designs

[a supprimer merci]

Une petite mise à jour sur ce DAC (Mosaic UV).

D'une part, Hifi-Advice, qui avait fait parler de la première itération du DAC (Mosaic T) n'a toujours pas obtenu un "review sample" de la deuxième itération du DAC (Mosaic UV), mais fait part des commentaires suivants sur son site (en fevrier):

"With the EC guys, one can never tell… They were going to send a review sample after the next modification that they were working on. Most likely they have again come across new developments that have triggered new ideas for the next product iteration and they are experimenting with this right now.

All I can say at this point is that the UV is very, very good. Much better than the original Mosaic. A mutual friend has one that he brings along every now and then. We have compared it to some very pricey DACs. It has always either held its own or actually beaten the more expensive product."

Effectivement, les frères Brown (ils sont donc deux), toujours à la recherche d'améliorations, sont en train de revoir le Mosaic UV pour:
- intégrer une alimentation sur batterie
- revoir les circuits du DAC afin de les rendre "insensibles" au signal USB en entrée.

Quelques explications obtenues par mail (en avril) sur ce dernier point:

"All DACs are sensitive to the USB audio source, even very expensive (Eur 30,000 and up) DACs from established brands. This occurs with verified bit-perfect playback so the only remaining cause for this has to be the ripple and jitter on the USB signal and the noise on the 5V USB bus voltage. The USB noise spectrum is the sum of all noise sources within the source and being fed into the source.

However, the 5V USB bus voltage is one of the causes that can be fixed easily.
the USB data also contains jitter and ripple that enters the USB audio receiver and all connected circuits because certain bandwidth is needed to get this data through. Circuits within the USB audio receiver add more harmonics (fast digital logic circuits).

Fast logic produces harmonics that extend far into the GHz range, these can spread very easily through stray capacitances throughout the circuits and wirelessly (EMI).

The most obvious cause for degraded sound is master clock degrading (increased jitter and ripple) as a result of the leaking USB data noise spectrum.

Then there is D/A converter circuit pollution through noise (increased noise floor, masking).

Everything connected to the USB audio source also has impact on the jitter and ripple on the USB signal, including WIFI and Bluetooth enabled on the source and hard wired connections to the source like LAN for example.

The best solution would be attempting to reduce DAC source dependency by making both master clock and D/A converter immune to this USB noise spectrum. This is what we tried to achieve with the new Mosaic II DAC.

And it seems we finally succeeded by placing the D/A converter in quarantine (electronic air lock circuit) and developing a novel sine wave clock with nested bandpass filtering (pure sine wave output) and multiple, isolated transformer coupled outputs with very low output impedance of less than 10 Ohms (transformation ratio). Load fluctuations are sensed through the output transformer and automatically compensate the oscillator frequency. This way the output frequency can no longer be influenced by the connected polluted clock loads."

Je n'ai pas de nouvelles depuis, mais j'ai hâte de pouvoir tester ce Mosaic II qui j'espère sera vendu à un prix aussi raisonable que ses prédécesseurs.

A suivre...