certainly something wrong with the samplerbox image i used.
I had run pimeroni script on it and double check the config, all was fine
i then decided to go from a standard raspbian distib, then set up the phat dac: that time, all went fine
and finally install the samplerbox appli
and now everything works fine
by the way, this samplerbox is great to use with phat dac. It is a great sampler that allows you to play whatever sound from a midi device connected to the Rpi