FiiO
FiiO Headphone Amps Portable DAC USB Type-C coaxial 384kHz/32bit (E10K-TC Black)
Fender
Fender Mustang Micro Headphone Amplifier, with 2-Year Warranty
Fosi Audio
Fosi Audio T20 Bluetooth Tube Amplifier Stereo Receiver 2 Channel Class D Digital Mini Hi-Fi Power Amp Preamp Compact Integrated Headphone Amplifier for Home Passive Speakers with 6A2 Vacuum Tubes
Douk Audio
Douk Audio U3 Mini Class A Headphone Amplifier HiFi Desktop Home Stereo Amp DC5V