Grace 901 replacement: Grace m902
Dec 6, 2004 at 3:41 AM Post #136 of 209
Hi all,
Here are the results of the USB jitter and bit tests. Please let me
know if proper etiquette would be to start a new thread with this sort of
technical stuff.

The Mac Power Book (OSX) will play 44.1kHz and 48kHz files over the usb
interface to the m902 with perfect bit accuracy. Again, as I mentioned
in a previous post, you must open the MIDI/Audio setup panel and set the
output sample rate to match the file being played or else sample rate
conversion occurs. (We will have these details in the owners manual)

SACD:
As far as I know there are no SACD players that have digital output when playing SACD disks with the possible exception of units with the I-link port. I think this is a firewire-like interface but the data is encrypted and (correct me if I'm wrong) asynchronous which would provide for jitter prone transfers. In the professional world DSD equipment uses SDIF-3 which consists of separate clock and data signals on BNC connectors. I think EMM Labs makes a modification for a SACD player so that it will output DSD data to a DSD dac...

USB jitter:
Measured at the spdif output of the PCM2902 the recovered clock from the PCM2902 measures about 240 pico seconds of RMS jitter when playing a 44.1kHz file and 390 pico seconds when playing a 48kHz file. Note that the 44.1kHz performance is very near to the noise floor of the Terrasonde Digital Audio Toolbox which is about 200 Pico Seconds when measuring spdif data streams. To really know the jitter of the PCM2902 would require access to the sample clock inside the chip. Oh well. However, this is not shabby jitter performance. I was expecting worse. With a good secondary PLL (like the s-Lock circuit) this can be reduced to less than 40 pico seconds.

If there was any confusion earlier in this thread, the usb interface is limited to a *maximum* sample rate of 48kHz and 16bit word length. 44.1kHz works fine. While there are USB solutions that support higher sample rates and bit depths, they are marginaly reliable. For higher sample rates and bit depths the only viable solution is IEEE 1394 (firewire) as it is designed for audio and video streaming. USB 2.0 will probably not become a popular audio transport for its lack of clear standards for audio streaming.


On another note a friend of mine who is a Linux guru is working on determining the requirements for making the m902 work with Linux.
I'll report as soon as we know anything.

Michael
 
Dec 6, 2004 at 4:37 AM Post #138 of 209
Quote:

Originally Posted by GoRedwings19
Thanks for replying to all the technogeeks. But my question is much simpler. Where can I get one considering I live in the UK?


I thought you lived in the Joe Lewis Arena... Taking a vacation while there is no NHL?
I'd contact Headroom.
smily_headphones1.gif
 
Dec 6, 2004 at 5:06 AM Post #139 of 209
Quote:

Originally Posted by mbgrace
I thought you lived in the Joe Lewis Arena... Taking a vacation while there is no NHL?
I'd contact Headroom.
smily_headphones1.gif



Sorry I live in the UK, The joe louis part is the home of my favourite hockey team. I compensated for the lack of NHL, I bought nhl2005 for the PC!
tongue.gif
 
Dec 6, 2004 at 10:03 AM Post #140 of 209
Quote:

Originally Posted by mbgrace
USB jitter:
Measured at the spdif output of the PCM2902 the recovered clock from the PCM2902 measures about 240 pico seconds of RMS jitter when playing a 44.1kHz file and 390 pico seconds when playing a 48kHz file. Note that the 44.1kHz performance is very near to the noise floor of the Terrasonde Digital Audio Toolbox which is about 200 Pico Seconds when measuring spdif data streams. To really know the jitter of the PCM2902 would require access to the sample clock inside the chip. Oh well. However, this is not shabby jitter performance. I was expecting worse. With a good secondary PLL (like the s-Lock circuit) this can be reduced to less than 40 pico seconds.


Michael, thank you so much for those results
smily_headphones1.gif
It looks like we'd better use that chip at 44.1KHz. Figures are indeed ok, I can continue with my little project.

I just saw that Gracedesign was established in Boulder, CO. Wonderful place, I've been studying for a year at CU, 2 years ago.
 
Dec 6, 2004 at 1:28 PM Post #141 of 209
Quote:

Originally Posted by mbgrace
On another note a friend of mine who is a Linux guru is working on determining the requirements for making the m902 work with Linux.
I'll report as soon as we know anything.



Great! I can't wait to hear the results.
 
Dec 7, 2004 at 6:23 AM Post #142 of 209
Quote:

Originally Posted by GoRedwings19
Hey with all due respect don't ever consider your self a "piker" (don't know what that means, tho!) not for one second. I am no better than the next headfier just because I have this system. When I joined headfi. All I had was a hd600 and a crappy av reciever. We all start somewhere! Why don't you try talking to me and then you'll see. I am just like you. I love ice hockey, I smoke (although not in the same room as the ML,tho), I have been warned about my swearing more times than I can remember, I love beautiful women, I love music.

But when you win the lottery can you give a few pennies. I would love to upgrade the 30.5 dac to a 30.6 dac
rolleyes.gif



To see you go from a crappy A/V receiver to Mark Levinson gives the rest of us all hope! In the meantime, we're all enjoying living vicariously through you--so keep up the good work!
600smile.gif


And if you love ice hockey, you're living on the right continent (OK I know you're on an island, but you're close).

Cheers!
 
Dec 7, 2004 at 12:56 PM Post #143 of 209
This is all I could ever ask for in a headphone amp. Something I've been dreaming about for many years.

But then, I am still dreaming about the kind of cash I need to buy one of these...
frown.gif
Maybe in a few years I'll be able to afford one.

And the new Sony cans as well.
wink.gif
 
Dec 9, 2004 at 11:01 AM Post #144 of 209
Quote:

Originally Posted by mbgrace
Teflon caps might sound better than the metalized polyethylene terephthalate but then again they might not. While the dielectric properties or teflon are nearly ideal the physical size of teflon caps can be problematic. Especially in balanced interfaces where physically large caps can degrade common mode rejection.
I can't condone this type of modification but I would be interested in hearing your results
biggrin.gif



Are there any mods for the 901 you think might be worthwhile?
 
Dec 12, 2004 at 8:30 AM Post #145 of 209
Quote:

Originally Posted by Jeff Wong
Are there any mods for the 901 you think might be worthwhile?


Hi Jeff,
I think the 901 is a very well balanced design. My personal unit is basically stock. Nevertheless, it might benefit from some Teflon capacitors or Cardas wire.. This would be a personal choice though and we are not currently providing this service.
 
Dec 13, 2004 at 1:46 PM Post #149 of 209
Michael - Thanks for the reply. For further clarification, where would you employ the Cardas wire (what kind of Cardas wire for that matter - I seem to recall there are several types), and which caps would you change? I haven't peeked under the hood yet to see what's inside. Do you have a schematic available?
 
Dec 13, 2004 at 3:15 PM Post #150 of 209
Ok, maybe these are dumb questions, but let me ask anyway. I was going to purchase a benchmark dac1 and probably a singlepower supra headphone amp. I'll feed the dac by spif by way of an m-audio 24/96 soundcard. Actually, I'm slightly wary of tubes because I like a lot of tight bass (I also listen to stuff from blues to Bach organ).

Ok, If I go with the Grace 902 will this unit handle jitter as well as the benchmark dac1? Two, am I right in that the line out can be fed into my amp for speaker listening? Three, is there a return period on this amp if ordered from Headroom?

This looks like a good deal. I'm actually anxious to try it out.

Noel
 
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