As some of you know this is exactly what I have implemented in my system. I have a home built DAC, the low jitter clock is in the DAC and feeds the SB3 as well, tapping in where the crystal usually goes. The I2S signals that go to the DAC chip are then tapped and fed to the DAC where they are reclocked by the main clock and sent to the DAC chip.
This works extremely well, the jitter on the clock pin of DAC chip is extremely low. I don't have an analyzer that can read jitter that low directly, but by looking at the clock spectrum I estimate it to be somewhere around 8ps. My original version just used a 1.5 foot ribbon cable between the SB3 and the DAC box. I have now replaced that with LVDS signals. The final jitter going to the DAC chips is the same, but the ribbon cable carrying full logic level signals radiated a fair amount and caused significant ground contamination. That pretty much goes away with the LVDS. As described this is fairly simple connection. Unfortunately that restricts you to one frequency. If all you do is listen to 44.1 CD music its fine. But if you listen to internet radio that is based on 48KHz sample rate, you are out of luck. My recent implementation gets around that, I have both a 11.2896 and 12.288 oscillator in the DAC, send both to the SB3. I also send the MCLK from the SB3 to the DAC (this is either 11.2896 or 12.288 depending on the sample rate the SB3 is using). The FPGA in the DAC determines which clock the SB3 is using (very simple circuit, a 8 bit counter clocked by the local 11.2896, and another clocked by the MCLK from the SB3, if the counts are the same, its the 11.2896, if the SB3 one is larger, its 12.288). This circuit muxes the two local oscillators to send to the DAC chips. It works quite well. The extra mux in the clock path should add a slight bit of jitter to the clock line, but I have not been able to either measure or hear that. An intersting side effect is that I can hear a significant improvement in the analog out from the SB3 when being fed the external clock, even with the jitter added by the trip from the clock to the SB3. I was expecting the jitter in the SB3 from the very unoptimized clock feed to be worse than its own clock, that didn't turn out to be true. So yes the architecture DOES work, and works very well. If you want to use a commercial DAC it will take some modification to make this work, exactly what is going to be dependant on the DAC of course. In many cases its not all that difficult if you are willing to give up 48KHz sample rate. John S. -- JohnSwenson ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=35642 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
