It's possibly the region setting on the Sansa Clip - when sold in the EU the output volume is seriously restricted.
If this is the case you will need to:
1. Reset the Sansa player to factory settings Settings > System Settings > Reset Factory Settings
2. Set the region as Rest of World.
3. Change volume setting to High: Settings > System Settings > Volume > High
Plenty of info if you google search 'Sansa Clip low volume'.