This is my first post in these forums. I recently bought the full Buffalo 3SE Pro 9038 kit, along with a Cronus and Hermes BBB interface. I just got the power supplies, Mercury, and the DAC card all set up, and did some initial testing.
I hooked up a SPDIF connection from a PC which was sending a full scale stereo sine wav, and things are basically working. However, I noticed when I raised the DAC volume level such that the peak voltage level crossed about 2.1V (full scale peak voltage when the DAC volume is all the way up is about 4,2V), all of a sudden a lot of harmonics poked up. I checked to make sure there was still some headroom on the Placid (i.e. shunt level hadn't gone down to far), but since this isn't a dynamically changing source, it doesn't really need a lot of headroom.
Anyway, I'm not really concerned right now, for two reasons:
1) My measurement methodology is highly suspect. Although the source signal looks really clean, I'm using a Digilent Analog Discovery 2 USB scope, which is certainly not the best for high resolution measurements (it's got a 14 bit A/D converter). It's quite possible that corssing the 2.1V line causes an issue in the USB scope, and nothing is changing in the Mercury output. I've also got a bunch on temporary, potentially suspect, wiring, and am using the SE outputs. On the other hand, nothing else is changing at that point, i.e. I have a clean signal at 2V peak, and it gets harmonically messy at 2.1V peak by just changing the DAC volume.
2) Even if the problem is real, and I can't find an easy fix, I can probably live with 2V output. I'm pretty sure that will drive my system to high enough listening levels.
In the future I will make better measurements, probably using a higher end sound interface, like my Focusrite 18i20 which can easily handle the peak output from Mercury (not sure I have any other easy ways to do this, since I don't have easy access to high quality test hardware), i.e. just take a long stereo sample at 96/24 and then run a static spectrum conversion with known good DSP software.
However, I wanted to post this just to see if there is something I should check, or if this isn't a surprise, or something else I am missing.
