Tír Na HiFi

Some time ago I think I mentioned that I had oscilloscope shots of the stock Vs modified Hiface & of the effect of RF attenuators. I couldn't post these pictures as they were to appear in a review. That review has now been published http://enjoythemusic.com/magazine/equip ... vo_dac.htm

So I can now post these pics of the SPDIF waveform on the output of the Hiface for those that are interested.
The first is the rise time of the modified Hiface:

The second is the rise time of the stock Hiface:



The scope shots in the review show the effect of the battery & the power supply mods - it speeds up the rise/fall time slope of the SPDIF waveform. A bit of explanation is required to understand what this means. The rise/fall time slope is where a change from 0 to 1 or 1 to 0 is determined - the decision point. Somewhere about half way up the slope of the line is the decision point.

In the stock Hiface the time from the bottom to top of the slope is 6.10ns - in the modified Hiface it is 3.92. I believe that the faster/steeper slope makes for a more accurate decision point with a better chance of it matching the timing of the decision point in the recording. Any variability in this timing match leads to jitter.

So the modified Hiface should have lower jitter SPDIF output but I don't have the equipment to measure this

The second set of scope shots show the effect of the RF attenuators. It reduces/eliminates the squiggles on the top of the SPDIF waveform. These squiggles are interpreted as reflections in the SPDIF signal path. If these reflections return to the DAc at the time the decision point is being read, it will superimpose on top of the slope & cause the decision point to shift somewhat. Again a cause of jitter. That damn jitter is just so ubiquitous & intrusive.

The first pic is the modified Hiface without RF attenuator:


The second with 10dB & 6dB Rf attenuators