Headphone Amplifier
iFi hip-dac2 Portable Headphone DAC and Amplifier
Amazon
iFi Hip-dac2 - Portable Balanced DAC Headphone Amplifier for Android, iPhone with USB Input Only/Outputs: 3.5mm Unbalanced / 4.4mm Balanced - MQA Decoder
Adorama
iFi AUDIO hip-dac2 Portable USB DAC and Headphone Amplifier