Sabre32 Unlocks: Looking for Gremlins

Recognizing that the Sabre32 DPLL setting is sensitive to incoming jitter, I devised a test to automatically measure the number of unlocks as documented here: [link]

As it is turning out, the unlocks do not seem directly related to the jitter of the transport because they seem random glitches and they show a strong correlation to electrical activity during the daylight hours. Either the noise in the electrical grid increase jitter or causes other anomalies causing the DPLL to loose lock.

In this post I will record and update different tests in order to determine what improves this un-lock behavior. Ultimately, if we can lower the DPLL bandwidth of the Sabre DAC, the level of jitter reduction will be increased, and that is a good goal.

TEST CONDITIONS

• Bufflalo II DAC powered with Placid at 5.25V.
• DPLL bandwidth: “LOW”. This is one notch above “LOWEST” since with this setting I am able to have unlock-free behavior for long periods of time (hours)
• Source: iTunes on Windows 7
• Transports: Musiland 03US
• Everything is plugged into a Monster Cable power conditioner
• [Click on images to see the original size]

MORE SHIELDING: (modding the case)

Originally, I had the DAC board without any casing affixed to the top of the power supply unit, just minimal shielding from a top plate as shown below (minus the Musiland MINI on top which I had upgraded to the Musiland o3).

Using another case for the DAC board (luckily I had a matching case :-)). I also elevated it from the PS unit below to keep the electronics a little further away from the transformers in the PS unit.

The Musiland 03 also fits neatly inside the case

Never hurts to add additional shielding. I put a metal plate to serve as more shield and to affix the output connectors. In addition, the plate makes contact with the Musiland case setting it a common EARTH GND potential (the Musiland is sitting on rubber feets) with the rest of the case. Also I wanted to isolate the output wires from the input wires.

With the cover in place. you can also see a ferrite I added to the input power to the DAC

Measuring the unlocks…

SHIELDING: SEEMS TO HELP

Suspecting airborne interference/noise (as also expressed by a commenter), I added some additional rudimentary shielding to cover the DAC board (just a metal cover that fully covers the top and the two long sides of the DAC board).

Here I plotted the best data set I had for the wee hours against the new data I got last night. There seem to be improvement. (This time, instead of looping a single song, I let iTunes play through the library -I wouldn’t think this would make a difference)

Notice that I only got 5 unlocks from 11:00 PM to 8:00 AM and there was a long stretch of almost 6 hours  without a single unlock. So we are “getting there”. I shall construct a case that fully encloses the DAC board…

LONG LEADS vs SHORT LEADS: NO DIFFERENCE

I shortened the I2S wires from about 9″ to 3″ to test if there are any differences in the unlock behavior. I also removed the ferrite bead I put in the bit clock wire as it seemed to make no difference (it seemed worse) and in addition, the ferrite might become a problem with higher sample rate material. As shown below, it doesn’t seem to make any difference

AM vs PM: NOISE IN POWER GRID

I let the computer collect more data as I went to work. No activity at home until around 3:00 PM. The Bitclock signal has a ferrite bead (which seems to make it worse – I will test it again without the ferrite bead). As shown by the data: the number of unlocks is strongly dependent on day vs night.

FERRITE IN BITCLOCK: NO BETTER (SEEM WORSE)

Attempted to deal with the power noise issue by inserting a ferrite bead in the bitclock wire (with two turns). The results are shown below. In total I recorded 249 unlocks with the ferrite and 174 unlocks without the ferrite. Since the data was taken in different days, I don’t think the difference is that significant.

What the data shows is a strong correlation between electrical activity during the daylight hours and much reduced activities during the night time hours especially after midnight. There is also a “break” during the daylight hours when people are out of the residential areas.