PURE vs Zero:RED: which needs more amplifier?

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 is only about what they ask of an amplifier — not how they sound, which no specification on either sheet can tell you.

The Zero:RED needs 5.5 dB more than the PURE to reach the same loudness — 1.0 mW against 0.29 mW.

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. 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.

The gap between these two in decibels does not change with volume — it is a property of the two headphones. What changes is the size of the numbers, and it changes fast: every 10 dB costs ten times the power. The row that matters is the one nearest the level you listen at, and for most people that is nearer the top of this table than the bottom.

The Zero:RED is more demanding than 43% of the 567 non-electrostatic models in this database; the PURE than 18%. Both figures use the same measure as the rest of the site: whichever runs out first against a 2 V, 100 mW dongle, voltage or power.

105 dB is included because forum power figures are usually quoted there or higher. It is also a level that damages hearing in minutes — how many minutes is its own calculator.

Of the 280 sources here, 280 reach 100 dB on both. That is the easy axis. 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 rest either fail one of those or never printed the number at all, and 208 of them are in the second group.

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.

Cheapest that satisfies three published numbers is not the same as best, and none of it is about how either headphone sounds. To put either model against a source this page does not mention, or to change the target loudness, use the amplifier matcher.

Each model has a page of its own with the full source list, the hiss estimate and the provenance of every figure above: 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.