Find your card with
$ cat /proc/asound/cards
To get valid ALSA card names, use aplay
:
$ aplay -l
and then create /etc/asound.conf
with following:
pcm.!default { type hw card 1}ctl.!default { type hw card 1}
Replace "card 1" with the number or name of your card determined above.
Alternatively, you can change ordering of your cards so your USB card will be card 0 and it will work without editing asound.conf
.