The Abyss AB-1266 Phi TC is 50Ω at 88.0 dB/mW; the HiFiMAN HE400se is 25Ω at 91.0 dB (no reference unit printed). This page is only about what they ask of an amplifier — not how they sound, which no specification on either sheet can tell you.
The Abyss AB-1266 Phi TC needs 3.0 dB more than the HiFiMAN HE400se to reach the same loudness — 16 mW against 7.9 mW.
| Specification | Abyss AB-1266 Phi TC | HiFiMAN HE400se |
|---|---|---|
| Impedance | 50 Ω | 25 Ω |
| Sensitivity | 88.0 dB/mW | 91.0 dB |
| Sensitivity (voltage) | 101.0 dB/V | 107.0 dB/V |
| Power for 100 dB | 16 mW | 7.9 mW |
| Voltage for 100 dB | 0.89 V | 0.45 V |
| Current for 100 dB | 17.8 mA | 17.8 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 6.25 Ω | 3.12 Ω |
| Sources that reach 100 dB out of 280 | 275 | 280 |
One caution before reading the rows. HiFiMAN HE400se printed a decibel figure with no reference unit, so this page reads it as per milliwatt. If it is really per volt, that model needs far more than the table says. Why the two readings differ by so much.
5 of the 280 sources have the power for the HiFiMAN HE400se but not for the Abyss AB-1266 Phi TC — Apple USB-C dongle (EU), Zoom AMS-22, Steinberg UR22C, 2 more.
1 source is low enough in output impedance for the Abyss AB-1266 Phi TC under the one-eighth rule but not for the HiFiMAN HE400se (Shanling H5).
275 of the 280 sources here reach 100 dB on both. That count is about power only — the output-impedance and hiss lines above are separate questions, and a source can pass this one and fail those.
Each model has a page of its own with the full source list, the hiss estimate and the provenance of every figure above: Abyss AB-1266 Phi TC and HiFiMAN HE400se. Each figure on this page is labelled on those pages with where it came from, including the ones Abyss and HiFiMAN never published — what Abyss publishes and what HiFiMAN publishes, both counted.