The Truthear PURE is 13.8Ω at 105.4 dB/mW; the Truthear Zero:RED is 17.5Ω at 99.9 dB/mW. This page covers what they ask of an amplifier, not how they sound.
The Zero:RED needs 5.5 dB more than the PURE to reach the same loudness — 1.0 mW against 0.29 mW.
| Specification | PURE | Zero:RED |
|---|---|---|
| Impedance | 13.8 Ω | 17.5 Ω |
| Sensitivity | 105.4 dB/mW | 99.9 dB/mW |
| Sensitivity (voltage) | 124.0 dB/V | 117.5 dB/V |
| Power for 100 dB | 0.29 mW | 1.0 mW |
| Voltage for 100 dB | 63 mV | 0.13 V |
| Current for 100 dB | 4.6 mA | 7.6 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 1.73 Ω | 2.19 Ω |
| Sources that reach 100 dB out of 280 | 280 | 280 |
Every source in the database that drives one of them drives the other. On power, the choice between these two changes nothing about what amplifier you need.
4 sources are low enough in output impedance for the Zero:RED under the one-eighth rule but not for the PURE (Schiit Vali 2+, Astell&Kern HC3, RME Fireface UFX II, 1 more).
5 sources stay below the audible-hiss threshold with the Zero:RED but cross it with the PURE (FiiO BTR11, FiiO K11 R2R, Schiit Valhalla 3, 2 more).
280 of the 280 sources here reach 100 dB on both.
The Zero:RED is more demanding than 43% of the 567 non-electrostatic models in this database; the PURE than 18%.
| dB SPL | PURE power | PURE voltage | Zero:RED power | Zero:RED voltage |
|---|---|---|---|---|
| 80 | 2.9 µW | 6 mV | 0.01 mW | 13 mV |
| 85 | 9.1 µW | 11 mV | 0.03 mW | 24 mV |
| 90 | 0.03 mW | 20 mV | 0.10 mW | 42 mV |
| 95 | 0.09 mW | 35 mV | 0.32 mW | 75 mV |
| 100 | 0.29 mW | 63 mV | 1.0 mW | 0.13 V |
| 105 | 0.91 mW | 0.11 V | 3.2 mW | 0.24 V |
| Source | Price | Headroom, PURE | Headroom, Zero:RED | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 16.5 dB | 12.1 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 28.6 dB | 23.6 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | $59 | 25.5 dB | 20.5 dB | 0.6 Ω | 1.0 µV |
Of the 280 sources here, 280 reach 100 dB on both. 65 of them also publish an output impedance low enough for both under the one-eighth rule and a noise figure that stays below the audible-hiss threshold with both.
The cheapest of the 65 is the JadeAudio JA11, at $20. It leaves 16.5 dB of headroom on the PURE and 12.1 dB on the Zero:RED, its output impedance is 0.5 Ω against a one-eighth limit of 1.73 Ω and 2.19 Ω, and its noise figure puts the hiss floor 11 dB and 18 dB below the 20 dB SPL this site treats as the point where a quiet room stops hiding it.
| Model | As printed | Tolerance | Standard |
|---|---|---|---|
| PURE | 7-40kHz (IEC61094, Free Field) | not printed | IEC61094 (free field) |
| 20-20kHz (IEC60318-4, -3dB) | -3 dB | IEC60318-4 | |
| Zero:RED | 20-40.5kHz (IEC61094, Free Field) | not printed | IEC61094 (free field) |
| 20-20kHz (IEC60318-4, -3dB) | -3 dB | IEC60318-4 |
Truthear prints two ranges, “7-40kHz (IEC61094, Free Field)” and “20-20kHz (IEC60318-4, -3dB)”, for the PURE and two ranges, “20-40.5kHz (IEC61094, Free Field)” and “20-20kHz (IEC60318-4, -3dB)”, for the Zero:RED.
Both sheets print a tolerance, which is rare enough to be worth pointing at: only 58 of the 490 models with a printed range do. These two ranges can be set against each other, because each of them says how far down the response is allowed to be at the ends.
Not a measurement; maker by maker.
Both have a page of their own. In full: Truthear PURE and Truthear Zero:RED. Every figure on this page comes from what Truthear published, or is derived from it — what that maker publishes, counted.