music volume level varies

first of all i’m totally happy with the player, its very cheap and the sound quality very high, batteries last very long and its nice and small in every way its the perfect player for me, the earplug headphones that came with the player are great too (high sound quality) and fit very good and comfortable

but i have 2 players : one of them plays at a very low music volume sound level , and the other plays normally (loud) 

is that a manufacturing /technical fault ? or is there something i can adjust in settings

  1.  Make sure the one putting out the lower volume has its Volume Setting set to HIGH (as opposed to NORMAL). This is in the Settinigs > System Settings menu.
  2. If it does not have a Volume Setting, you may have set the Region to Europe, where there is a gov’t.-mandated volume (or decibel) limitation. Find the Reset Factory Settings option (also in the System Settings menu) and reset them. Choose either North America or Rest Of World to get your HIGH volume setting back.

Do they have different equilizer settings? How about Replay Gain settings?