iPod Touch 5 vs iPhone 5s sound output (Line Out)

I bought an iPod Touch 5 two months back, I love the sound quality of the device. But after 1 month when my brother bought iPhone 5s, I checked the sound output of the device through the same earpods that came with my iPod. The difference in sound output was huge, I am not talking about the sound quality but the loudness.

I checked everywhere but there was no proper explanation why the difference in sound is so huge.

Is it because the two DACs r completely different or is it something to do with Output Source Impedance?