Hi,
Yes, it should work just fine under Linux (as I know people use the PCM2707 under Linux), but I have not been able to confirm it yet. I should be able to soon. I think Brian has a module on the way to me. 🙂
BTW, we are taking orders now as all the components are tested and working fine.
I will be writing up some DOCs in the next day or two to put up on the site.
Cheers!
Russ
Yes, it should work just fine under Linux (as I know people use the PCM2707 under Linux), but I have not been able to confirm it yet. I should be able to soon. I think Brian has a module on the way to me. 🙂
BTW, we are taking orders now as all the components are tested and working fine.
I will be writing up some DOCs in the next day or two to put up on the site.
Cheers!
Russ
This site seems to sell a 12.000MHz Guido Tent Labs XO clock for 29.00EU. As I understand it these seems to be a "very high quality" clock crystal. Would it be worth implementing one of these as an upgrade to the USB receiver? Would it be a drop in replacement for the existing crystal (my gut says no, because this clock has four pins and the existing has two)?
http://www.dddac.de/ddsales.htm#shop
http://www.dddac.de/ddsales.htm#shop
m0tion said:
Guido's oscillator requires a voltage supply. To be honest, the DDDAC implementation is rather better than that of Twisted Pair.
Dan
Spartacus said:
Wow, better in what way exactly? Do you have both to compare? Are you talking about the I2S output which is the primary design criteria for the Opus USB-BP(Bus Powered) module?
Is this meant to be an objective statement?
Have you measured or scoped the digital clock/signals coming out of both units side by side?
It may "look" better on paper, but if you actually measured the resulting I2S output I seriously doubt it is any better at all, which is really the purpose of our USB receiver, I2S output to feed the "real" DAC.
I would however expect the analog output to be slightly better with a self powered USB DAC. Someone looking for a PCM2707 only solution would be better off looking for a self powered solution if the very best ANALOG performance you can get out of a PCM2707 is their goal.
The answer to m0tion's question is that yes, you could use whatever clock you like, powered or non, it would just require removing the old clock and wiring up the new one. Though I seriously doubt its worth the effort.
BTW someday we may decide to do a bit "higher end" self powered USB DAC, but there is only so far you can take the PCM2707 so it will likely be a different solution.
BTW It not terribly important to me if our USB DAC is any better than anyone else's, but it is a perfect fit for the Opus Stack. If I were going to make a claim a superiority I would have to base it on something significantly more substantial and credible then the 'perceived' benefit of some fancy schmancy clock. 🙂
Also, please don't forget the incredibly underestimated merits of simplicity.
Cheers!
Russ
Russ, no offence intended.
I've built a DAC based on the DDDAC. I didn't use the USB section, but I've studied the diagram.
Doede Douma in his write-up of his DAC found that the quality of the 12MHz XO* is of some importance.
My comparison is based on an understanding of digital engineering principles, and quite simply the DDDAC usb section is better in various details. Of course it may not sound better to everyone, and is rather more complicated.
As for fancy schmancy clocks, I've been making my own since before Guido started selling his.
I hope you're still happy to sell me some of your excellent kits!
Kind regards,
Dan
* was DAC - changed to XO
I've built a DAC based on the DDDAC. I didn't use the USB section, but I've studied the diagram.
Doede Douma in his write-up of his DAC found that the quality of the 12MHz XO* is of some importance.
My comparison is based on an understanding of digital engineering principles, and quite simply the DDDAC usb section is better in various details. Of course it may not sound better to everyone, and is rather more complicated.
As for fancy schmancy clocks, I've been making my own since before Guido started selling his.
I hope you're still happy to sell me some of your excellent kits!
Kind regards,
Dan
* was DAC - changed to XO
Spartacus said:
Oh I bear no grudges. 🙂 They never are beneficial. And I am sure that Doede Douma's gear is top notch. But the designs are different with different goals. So claims of "better" need to weigh the facts, and those need to be demonstrated with more than anecdotes.
Oh yes, so have I studied his schematics. And if I were doing a self powered USB module I would probably make some of the same choices as he (and I can see some things I would improve), but I would require much more solid evidence than someone's "say so" that such and such has a significant effect. I would need to see it.
The clock as implemented is already extremely accurate. And we use a well regarded crystal. So I am saying that the degree of difference would be small indeed.
Please expound on "various details" as I would love to learn.
Cheers!
Russ
AFAIK the 12.000 MHZ clock from TentLabs is not available anymore. It is a custom clock not listed in standard production and I saw somewhere on their site that they were no more able to produce custom products.
Me too thinking to a clock upgrade, but PCM2707 wants a non "standard" crystal. Curious: it requires 12.000 MHZ on input, but its master clock output (SCLK) is a standard 11.2896 MHz.
Why this? I suspect 12mhz are to receive 48khz Windows standard audio, while 11.28mhz is to output standard 44.1khz (master clock and sample rate must be multiple). I'd like to learn more about this, but, IMO, there is no way to add an external clock to PCM2707 like you do with a CDP.
Dan,
I own both the two versions of DDDAC USB boards and I’m listening to OPUS DAC with the last one. Nonetheless I ordered two OPUS USB, because of their "minimalist" design. I don't think the PS will be so important in the digital domain. Anyway I have to wait until the end of September for a comparison, unlike Brian is able to deliver in Italy in less than three weeks
Me too thinking to a clock upgrade, but PCM2707 wants a non "standard" crystal. Curious: it requires 12.000 MHZ on input, but its master clock output (SCLK) is a standard 11.2896 MHz.
Why this? I suspect 12mhz are to receive 48khz Windows standard audio, while 11.28mhz is to output standard 44.1khz (master clock and sample rate must be multiple). I'd like to learn more about this, but, IMO, there is no way to add an external clock to PCM2707 like you do with a CDP.
Dan,
I own both the two versions of DDDAC USB boards and I’m listening to OPUS DAC with the last one. Nonetheless I ordered two OPUS USB, because of their "minimalist" design. I don't think the PS will be so important in the digital domain. Anyway I have to wait until the end of September for a comparison, unlike Brian is able to deliver in Italy in less than three weeks
thomaseliot said:
The 12MHz clock is for the USB interface, which runs at 12Mbps (not sure how many signals/s but it's obviously an integer multiple). Audio timing on USB is pretty...poorly designed... The device is supposed to sync its PLL to the start of the frames it receives over the bus, which will obviously not have very consistent timing. I think that on the PCM2707 the PLL is referenced by the 12MHz crystal, but it may be free running, it didn't seem clear from the datasheet.
I don't think replacing the crystal on the USB interface will give you any SQ gains. Its purpose is timing the USB bus; the timing of the audio signal is heavily dependent on the timing of the USB signals from the host.
Personally this is why I'd prefer the SPDIF interface; a dedicated soundcard probably has a reasonable clock at an audio frequency, while USB audio timing is (mostly) software controlled, or at best a weird-factor PLL based on a 12MHz clock. Also, SPDIF data is sent continuously at constant frequency, so designing a good PLL would be much easier.
error401 said:
I am with here, I think you could do what you want with our SPDIF module.
This is why I was saying that worrying too much about that 12mhz clock is a losing battle. But that said, our implementation is not at all bad, far from it... 🙂
Cheers!
Russ
Russ, would you mind commenting on what soundcard(s) you run, and how the SPDIF output sounds going into the Opus, vs the USB into the Opus? Maybe you've commented on this before, in which case...sorry 😛
Hello Russ,
The 12MHz clock is a reference for the PLL, the performace of which will have a direct result on the output clock. In your implementation, the active part of the Oscillator is on the 2707, so will get its power from that part. Oscillators like a very clean supply, hence noise on the 2707s PS will affect its jitter performance. A seperate clock with it's own power supply is optimal here.
Also it's good practice for emi reduction to use small resistances in the data/clock output lines.
Again, this is all tech talk, and doesn't mean that any particular circuit will sound bad.
Most PCs have a S/PDIF output anyway, and the Wolfson DIR you use looks especially good.
Dan
The 12MHz clock is a reference for the PLL, the performace of which will have a direct result on the output clock. In your implementation, the active part of the Oscillator is on the 2707, so will get its power from that part. Oscillators like a very clean supply, hence noise on the 2707s PS will affect its jitter performance. A seperate clock with it's own power supply is optimal here.
Also it's good practice for emi reduction to use small resistances in the data/clock output lines.
Again, this is all tech talk, and doesn't mean that any particular circuit will sound bad.
Most PCs have a S/PDIF output anyway, and the Wolfson DIR you use looks especially good.
Dan
error401 said:
Pros and cons 🙂
If you want a silent PC music server without fans , it gets quite hot for a sound card. I burned my Emu1212m there. Whith SPDIF you have the clock in a high EMI box at least 1m. and 2 or 3 IC away from DAC, while USB clock is quietly 5cm from the DAC. An IC must extract the clock from SPDIF signal, while USB I2s has its own 2 cm cable.....
Searched a bit and found that Wolfson produced a new evaluation board for the 8740 with USB input. The chip used is the TI TAS1020B and is powered by USB bus.
Spartacus said:
1) I am not sure what makes you think the internal regulator of the PCM2707 is not suitable for providing "clean" voltage to the crystal. It appears to be pretty clean to me.
2) The series resistance on the signals is there its, just at the DAC end.
3) Thanks! 🙂
All of this is constructive, so I really do appreciate it.
It may interest some to know that all this "good clock" "bad clock" talk has made me consider asynchronous re-clocking using something like a SRC4192 as a separate module with the input in slave mode on the output in master mode with a good reference clock.
Something like a ECS2100C should work fine as a clock source, and you could drop in a Tent clock if you like. I would expect this approach to pay bigger dividends then a nice 12mhz clock on the USB module, as we all know the 2707 is not perfect in any regard, yet perfectly suitable for what it is.
Cheers!
Russ