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seppstefano 7th April 2006 03:29 PM

Clock mastering
 
Hi all,
first of all I'd like to beg your pardon if I'm asking things already passed on these screens, but I couldn't find them after several threads and docs reading.

I've a "classic" cfg.: a cdp (marantz 94); a dac (Monarchy 22B, PCM63k); in between I have a Monarchy Upsampler. (all) connection is done with usual spdif, and would like to improve the performance of the combo.

I've read of several hi-performance (low jitter figure) clock modules, Tent, LC Audio, Hagerman, etc.. and several sources on the web for theory/ideas.

I'd like to know your opinion on a cfg based on a hi quality clock for the dac, directly (I mean without using a PLL approach) mastering the cdp. Assuming that this make sense, about practical implementation I found on the description of Tent XO3, when meant for a CD player:
"XO3 is equal to XO2, but contains an additional reclocking circuit for the digital output (SPDIF). This circuit reduces the jitter at that output. The incoming jitter at the DAC will be lower, resulting in better sound."

In this case (assuming the clock freq. are the same, a thing I still have to check), wouldn't it be possible to place the XO3 in the dac and use the reclocking output to feed the clock to the cdp?

Sorry for all my dummy questions and thanks for any feedback,

Stefano

Alexandre 7th April 2006 05:06 PM

Ciao Stefano.

So, you want to place the clock in your dac and slave the transport. I´ve been working on this, I don´t want to spend any money on a commercial solution. If you can spend a couple hundred euros, take a look at http://www.tentlabs.com/Info/Articles/Tentlink.html. This is the easy, proven way if you can afford it. Though you will need modifications, if feasible at all, to be able to use your upsampler with the tent labs setup.

Another way to do it is sending the clock back to the player by coaxial cable. Yes, you could possibly take the 11.2896 MHz out of the XO3 and send it to the player. But this is difficult to implement properly because of the high bandwidht connection between separated boxes. You need proper EMI and grounding measures. This is not as clean as the tent labs solution which only sends a control voltage to the VCXO on the transport.

The third way is to use optical interconnects between the transport and dac, like John Westlake used on the cambridge audio isomagic?. You won´t have groundloops and RF going out of the boxes. This is also hard to implement though.

I hope this helps.
-Alexandre

seppstefano 10th April 2006 07:10 AM

Ciao Alexandre,
many thanks for your kind answer and explanations.

I'll look for some more info on the optical transmission, even if I think that in my case I might be lucky even with a simple digital cable (being the units as near as 15cm).

In the weekend I read something on Tentlink and understood why the VCXO (Linn should do it in the same way).

Any suggestion for buffer/inverters fine for regenerating the signal and isolating from the main clock?

Thanks again for sharing,

Stefano

Alexandre 10th April 2006 04:44 PM

Ciao Stefano.

This really is a complicated effort that you´re planning. Keep in mind that you need experience and good skills to successfully modify an expensive piece of gear. I am not experienced enough to do this, and that´s why I am building from scratch, and not modifying anything.

Having said that, I think you can stick to cmos logic, 74hc04 inverters for buffering the clock, 74hc74 flip-flops for reclocking. There are others using AC and ABT logic tough. Maybe someone else can help us on this one. Be sure to draw all the timing diagrams, know what you´re doing (also consider the propagation delay).

I understand that you will reclock the spdif stream, inside the dac, before the digital receiver. Is this correct? Spdif reclocking is normally done inside the cd player and not inside the dac. I am not sure what benefits you can get by moving the masterclock and spdif reclocker to the dac box. Maybe you will get less interference from the noisy circuitry inside the cdp, but you will have the added trouble of sending back the clock to the player.

A good low-noise supply for the clock and reclocker is most important. Take a look at the interesting page by forum member Peufeu:

http://peufeu.free.fr/audio/extremist_dac/

Have in mind that Peufeu is not reclocking spdif, but I2S (between digital receiver and dac chip). Be sure to read Guido Tent´s document on supply decoupling also!

Good Luck!

seppstefano 11th April 2006 02:37 PM

Ciao Alexandre,
many thanks for your feedback, to be honest I've already bored Pierre...

Have a nice afternoon,

Stefano


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