Very happy with this amp signing my first steps in the world of good sound lovers. While waiting to buy me the beautiful helmet so I dream, I already noted an improvement in the quality of listening (Symphonic Power Metal FLAC on iPhone with QC15). The instruments come off much better and feeling of ringing in the ears after mounting the volume is nonexistent. This is not purely subjective, but the ears tire less. However, I take one star because the product sent is not the one ordered: the E11K iso E11. no easy access to the battery and different settings.