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AR-T Legato II USB-S/PDIF Converter

post #1 of 85
Thread Starter 

I have the privilege of being the first customer to receive AR-T's Legato II USB-S/PDIF converter.

 

For those who has no idea what the Legato is, it is a reference grade redbook (44.1K) transport for the computer audiophiles.  Legato II continues with the same tradition as a redbook only transport, but has upped the ante considerably in terms of sonic quality.

 

Why no high-res?  Many of you may ask.  The man (Pat) who created this is a strong believer in jitter.  It is the gremlin why digital audio sounded "digital", instead of being "analog".  When jitter is extremely low, the sound of a digital transport will become very analog, even a high-res device would have hard time matching the performance.  And I was told a lot of this has to do with some physics at work.  Suffice to say, it is "easier" to achieve extremely low jitter with a lower frequency clock than with a higher frequency one.  And a higher frequency clock is needed for a high-res device.  So it becomes very difficult to find an extremely low jitter clock for a high-res device, unless some expensive custom made SC-cut crystal or custom OCXO is involved.  The Legato II is designed to be affordable (US$799), so that precludes the use of such clocks/crystals.

 

So what sort of jitter figure do I get for the Legato II?  Audiophilleo quoted their USB-S/PDIF converter having 2.6pS RMS phase jitter from 10Hz to 100KHz.  The Legato II measured the same way will have around 0.05pS (or 50fS), about 50 times lower.  Not only that, Pat specifically measures phase noise down to 0.01Hz to ensure it is nice and clean at that level.  But mostly, he makes sure the phase noise at 1Hz is as low as possible.  This is achieved via extensive bin sorting, involving large quantity of crystals in order to find the ones that can make the grade.  It is like finding diamonds in the dust.  It is a very labor intensive process.

 

I do not know any audio manufacturer who will measure phase noise down to 0.01Hz.  MSB measured their $9995 FemtoSecond Galaxy Clock module down to 0.1Hz.  MSB's Femto Clock reaches -67dBc at 0.1Hz.  My particular Legato II reaches -55dBC at 0.1Hz.

 

Besides having a superior clock, Pat also ensures minimum signal reflections along the signal paths, tight control of the output impedance, and high return loss to guard against impedance mismatch on the receiving equipment.  All these painstaking details are required to achieve the superlative sound of the Legato II.

 

The version I received is actually using the final prototype board.  The production version will have the same circuit design, but there will be a slight position change of the charge LED and the rear panel lettering will be different.  It will have anodized labels instead of laser engraved labels.  Mine was a one off unit that Pat was playing with the idea of laser engraving.

 

So what has changed from the Legato (v1) to Legato II?  Legato II is now powered entirely by a SLA battery.  A 6v 7.2Ah unit to be exact.  With a fully charged battery, one can expect the Legato II to play music continuously for 3 days straight.  The unit charges the battery when the PC is not playing music or when it goes into standby/sleep.  There is an external 9v DC charger for this purpose, instead of getting the charge from the USB bus.  The will ensure the unit will get charged irrespective of the status of the PC.

 

Besides the battery powered supply, there is now a second BNC output on the Legato II.  It is labeled "Direct".  The other BNC output is labeled "XFMR".  XFMR means the output is digital pulse transformer coupled.  This output is the same as the Legato.  The pulse transformer is there to provide galvanic (ie: ground) isolation between the transport and the DAC.  It is there to avoid ground noise contamination.  The Direct BNC output does not have a pulse transformer.  It assumes the gear downstream (a DAC in most cases) will already have a pulse transformer in it.  In order to isolate the ground connection, all we need is one pulse transformer in the coax signal path, we do not really need two.  An extra pulse transformer can add distortion to the signal (even when the distortion is minuscule) and will also slow down the rising edge of the pulse.  So why is it so important to have a fast rising edge?  Well, Pat told me that an ultra low jitter clock signal has a very fast rising edge, in the <1ns range.  By having an extra pulse transformer in the S/PDIF path, the rising edge will inevitably be slowed down.

 

Ok, enough of the background info.  So how does it sound?  Well, it sounds very analog indeed.  So much so that I thought I was listening to vinyl with a nice turntable setup.  Everything flows with ease and yet it can be wild and dynamic if needs be.

 

I also happen to own the very last revision of  the Legato (internally, this was labeled as rev 2).  The Legato II has smoother treble (the last bit of digital glare is gone), a darker background revealing more details, longer decay/reverbs, more holographic sound stage, more dynamic sound and deeper bass.   The tone density is also higher, with a more engulfing sound stage.  The most striking difference to me is how much more ease in the presentation, and how much more analog it sounds.

 

Some of the sonic references that I am familiar with include: the Sony CDP-R10/DAS-R10 CD transport/DAC, Anedio U2 USB-S/PDIF converter, Anedio D2 DAC, Berkeley Alpha USB-S/PDIF converter, Alpha DAC series 2, Weiss DAC202, and MSB DAC IV Signature.  Many of them are superb top-of-the-class devices, but none gives the same vinyl-like presentation as the Legato II does.

 

I have also auditioned the ClearAudio Statement turntable a couple years back.  It is probably the best sounding analog source I have heard.  The Legato II is no ClearAudio Statement TT, but it has many of the same sonic attributes that I find a joy to listen to.

 

As usual, YMMV.

 

Rear panel view:

 

Inside the Legato II:


Edited by Viper2001 - 9/20/12 at 10:12am

Gear mentioned in this thread:

post #2 of 85

nice review, thanks

post #3 of 85

Were you ever able to compare your previous model with the off ramp 5?

post #4 of 85
Quote:
Originally Posted by Viper2001 View Post

... there is now a second BNC output on the Legato II.  It is labeled "Direct".  The other BNC output is labeled "XFMR".  XFMR means the output is digital pulse transformer coupled.  This output is the same as the Legato.  The pulse transformer is there to provide galvanic (ie: ground) isolation between the transport and the DAC.  It is there to avoid ground noise contamination.  The Direct BNC output does not have a pulse transformer.  It assumes the gear downstream (a DAC in most cases) will already have a pulse transformer in it.  In order to isolate the ground connection, all we need is one pulse transformer in the coax signal path, we do not really need two.  An extra pulse transformer can add distortion to the signal (even when the distortion is minuscule) and will also slow down the rising edge of the pulse.  So why is it so important to have a fast rising edge?  Well, Pat told me that an ultra low jitter clock signal has a very fast rising edge, in the <1ns range.  By having an extra pulse transformer in the S/PDIF path, the rising edge will inevitably be slowed down.

 

 

Some of the sonic references that I am familiar with include: the Sony CDP-R10/DAS-R10 CD transport/DAC, Anedio U2 USB-S/PDIF converter, Anedio D2 DAC, Berkeley Alpha USB-S/PDIF converter, Alpha DAC series 2, Weiss DAC202, and MSB DAC IV Signature.  Many of them are superb top-of-the-class devices, but none gives the same vinyl-like presentation as the Legato II does.

Viper

Nice review, thanks!

 

Questions:

1) Did you use the "Direct" BNC connector with the Anedio D2? (i.e., I assume the D2 does have an internal Pulse Transformer, correct?)

2) Did you tried [SBT+EDO] as a source?... If so, How does the LegatoII compare to your USB-modded D2?

(i.e., [SBT+EDO]-->USB-->[LegatoII]-->BNC-->[D2] vs [SBT+EDO]-->USB-->[D2])

post #5 of 85
Thread Starter 
Quote:
Originally Posted by tme110 View Post

Were you ever able to compare your previous model with the off ramp 5?

 

I don't have OR5 to compare with.  Does anyone know how OR5 compare with Berkeley Alpha USB?  They're in the same price range.  I can only tell you that the Legato II is better than the Alpha USB.  Alpha USB has a hint of glare on certain vocal tracks I played.  It also doesn't give me the vinyl/analog feel.  The Alpha USB I listened to was paired with Alpha DAC series 2 together with Spectral pre + mono blocks and Magico Q5 speakers.

post #6 of 85
Thread Starter 
Quote:
Originally Posted by LeoDuran View Post

Questions:

1) Did you use the "Direct" BNC connector with the Anedio D2? (i.e., I assume the D2 does have an internal Pulse Transformer, correct?)

2) Did you tried [SBT+EDO] as a source?... If so, How does the LegatoII compare to your USB-modded D2?

(i.e., [SBT+EDO]-->USB-->[LegatoII]-->BNC-->[D2] vs [SBT+EDO]-->USB-->[D2])

1) Correct

2) I have been using SBT+EDO as source, which I did not mention in the review.  The Legato II has cleaner and taughter bass when feeding the D2 via BNC coax.  It also sounds more vivid.  That's comparing to USB input to the D2.  My current U2 mod is using the ultra low noise IC regulators, not super regulators.  I have not get around to swap the IC regs with super reg to hear for the differences.

post #7 of 85
Thanks Viper, do you know what the wait time is like? Looks great in black.

Also, with SBT+EDO, does it recognize as a USB TWO device or do you need to use a hub work around?
Edited by Orangecrush - 9/21/12 at 5:47pm
post #8 of 85

Whats the cost of that converter?

post #9 of 85

according to the first post above it's $799

post #10 of 85
Thread Starter 
Quote:
Originally Posted by Orangecrush View Post

Thanks Viper, do you know what the wait time is like? Looks great in black.
Also, with SBT+EDO, does it recognize as a USB TWO device or do you need to use a hub work around?

 

I think the wait time is likely to be over one month.  Currently, 5 of my friends have pre-orders with Pat, so he is busy trying to fill the orders.  I don't know how many more folks are in the waiting list.  I think Pat mentioned to me that the initial batch will be a run for 25 units.

 

SBT+EDO recognize it as a Class 1 device, but it is strange that I never have to use a USB hub for it to work even for Legato v1.

 

Currently, there is an outstanding issue with SBT+EDO.  SBT does not turn off its USB output even when you put it to sleep.  The Legato II thinks the Link is still active and thus does not go into charge mode unless you unplug the USB cable.  Pat was made aware of the issue and I suggest using a timer such that when it detects no music is streaming for say 15 mins, it'll go into charge mode.  This is done by monitoring the Stream Active pin in addition to the Link Active pin on the USB controller (ie: these signal pins are provided by Gordon Rankin's Streamlength code).

 

I contacted the EDO developer, and he told me the issue has to do with the SBT firmware (ie: does not turn off the USB port or terminates the link on sleep).  Since we're at the end of the road for SBT, we cannot expect the firmware to be enhanced at this point.  Pat is going to try my suggestion.  Nothing was promised to me, but I've faith that it'll eventually be addressed on the production models.


Edited by Viper2001 - 9/23/12 at 10:10am
post #11 of 85

Thanks Viper2001 for your insights and review. You offer a  perspective into digital audio that is refreshing. It is not surprising that you are a devotee of Pats designs which stem from, if not totally unique philosophy, a purist singularity of vision applying the practical application of his experience. While not pretending to totally understand everything discussed, Pat has a way of explaining to the layman the complexities of design in a graspable way, as well as a wry sense of humor that makes his previous posts on Audiocicle a delight. A few questions.

Have you tested the Legato II using a simple USB out of a "typical" computer?  Excuse my naivete, but since the II goes to great lengths to isolate both the source and DAC, is it really required to use something like the Touch to stream audio? I realize that the Squeezsebox  platform offers a convenient way to organize files, but can't the same quality be obtained from using Foobar streamed to the USB port of a typical computer?    

post #12 of 85

the squeeze box is just there so you don't have to have a computer there instead
 

post #13 of 85

I guess what I'm asking then, is the same SQ available without buying a Touch?

post #14 of 85
Thread Starter 

I've not used a PC for testing the Legato II.  My past experience has told me that there is a lot of variation in sound when you used a PC.  The software player you used, the optimization of the OS, etc., can affect the sonic quality.  Some people said the best sounding platform is Linux Ubuntu with a realtime kernel.  SBT+EDO is essentially a Linux PC running a realtime kernel.  It saves myself from buying a dedicated PC, which is going to cost more and requires more maintenance.

 

The Legato and Legato II do not draw power from the USB port.  They are entirely powered by the power supply circuit or battery inside.  So the effect on using a different host for playback is smaller.  But both Pat and I know that the USB cable and the host device do make a difference in sound.  So it is like any audio components, some mixing and matching is required to get optimal sound.


Edited by Viper2001 - 9/25/12 at 12:10am
post #15 of 85
Quote:
Originally Posted by Viper2001 View Post

But both Pat and I know that the USB cable and the host device do make a difference in sound.  So it is like any audio components, some mixing and matching is required to get optimal sound.
Are you getting best results (SQ-wise) with your Furutech GT2 cable?
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