Phatbeat configuration for mopidy

Hi, I followed this guide (Streaming Spotify to your Pi) to install Mopidy on Pirate Radio.
The default volume level was very (very!) loud so I opened the config file (/etc/mopidy/mopidy.conf) and found an error as it was using the ‘software’ mixer instead of ‘alsamixer’.
My config file now is:

mixer = alsamixer

enabled = true
card = 0
control = Master

Now the output volume level is in sync with ALSA and I can change it with alsamixer in ssh.
The problem is that now I can’t find the name of the ALSA control to use inside mopidy.

Sep 15 17:30:51 pirateradio mopidy[493]: ERROR    [MainThread] mopidy.commands Mixer (AlsaMixer) initialization error: Could not find ALSA mixer control Master on card 0. Known mixers on card 0 include:

As you can see known mixers on card 0 are none! If I run this command (according to GitHub - mopidy/mopidy-alsamixer: Mopidy extension for ALSA volume control):

pi@pirateradio:~ $ amixer scontrols
Simple mixer control 'Master',0
Simple mixer control 'Capture',0

Maybe the problem is that I’m using Pulseaudio?