[Alsa-user] PCM2707C + PCM1794A Crackle Problem

[Dario E. <al...@ka...>]

Hello dear Alsa-List,

i have built a "Jedac", a DIY-USB DAC consisting of TI/Burr-Brown
PCM2707C for USB interfacing as well as the PCM1794A for the actual
conversion. The original author has some more documentation including
schematic and PCB-Layout here:
http://users.abo.fi/jskata/JEDAC/

I've been using the DAC for a while now. Recently, i've noticed that i
get a slight "crackle" in the background. Only when listening to music.
It sounds ... a little like a bad, old Vinyl. A slight, medium- to high
pitch crackle. Its most audible in quieter portions of the track, but
i'm pretty sure its also existent in the louder parts, just that the
human ear has a harder time picking it up there.

Anyways, on to my setup. While i currently use pulse (please don't start
to run away screaming now!), i've completely purged and deactivated all
pulse components for testing, and only used plain alsa. I've run
alsa-info.sh and uploaded the result to your upload-service. Please see
here:
http://www.alsa-project.org/db/?f=43646f24d54c2d65841ae36ff44670bcb6321145
It also shows my onboard soundcard, which i don't use, as well as the
"freshly" plugged in "BurrBrown from Texas Instruments USB AUDIO DAC".
While i currently use kernel 3.16-2, i've also tried an older version
where i could still set nrpacks=1. I've tried autoclock=0/1 as a module
parameter as well as power saving in the older versions. I also use
"powertop" every time to make sure the USB autosuspend is turned off for
all USB-related devices (this is a desktop, but still, powertop has a
nice interface for such things :D).

I'm now at a total loss of ideas. A nice fellow in #alsa (@Freenode)
suggested i either mail here, or try to use "USBMon" for debugging the
problem. After a fair share of reading into USBMon and general USB
debugging on Linux, i don't think i have the necessary protocol
background to be up to the task.

So, i'd be really really grateful for any help on finding and possibly
solving the issue.
Thanks for reading, and Best Regards
-Dario Ernst

PS: Please excuse my bumpy and broken english. As its not my native
tongue, i'm always struggeling a bit :D.