Just got this little guy for work to make my day's a little more enjoyable. https://www.amazon.com/Multi-Hybrid-Headphone-Amplifier-Audio-Preamplifier/dp/B07DLRFHXT Working voltage: DC24V, 1.5A at least Input sensitivity: 50mV; Gain: 32dB; Input Impedance: 100KΩ Frequency response: 10Hz-60KHz (±0.25dB) Audio input: 3.5mm audio jack & Stereo L/R RCA Audio output: 3.5mm headphone & 6.35mm headphone & Stereo L/R RCA Output Impedance: 20Ω~600Ω; Signal/Noise Ratio: >90dB Dimension: W102× D102 × H37.5 mm (4.02 × 4.02 × 1.48 in) Net Weight: 310g (0.68lb) The sound is not great (neither are my earbuds) but there is very noticeable hum that is driving me nuts. The output impedance: 20Ω~600Ω. My earbuds have a Nominal Impedance of 16ohms. Is this likely the cause of the hum? I tried some cheap over ear headphones last night with phone as source and I think they had hum ass well. Strange thing is, while sitting here typing this post with music stopped, the hum drops down to an acceptable level. When I turn the music back on the hum comes back and remains even after stopping the music for about a minute or so. Source is iMac/Spotify App headphone jack out to Nobsound. It's like the hum source is being shut off from either the iMac or the Nobsound until the music starts. I need new headphones anyway. Should I buy them first or consider returning the amp? Any more tests I can do?