Collection Matcher

Most amplifier advice assumes you own one pair of headphones. If you own four, the question changes: not “what drives this” but “what drives all of it” — and the answer is usually decided by whichever pair is the fussiest, not the hardest to drive. Add the headphones you actually own and this works out which sources suit the whole shelf at once.

What is being tested

Each source is put through three separate tests against every headphone on your list, and it has to pass all of them for all of them:

• Power. Enough to reach 100 dB SPL — genuinely loud, louder than most people listen — into each pair’s impedance.
• Output impedance. Below an eighth of each pair’s impedance, the rule of thumb for leaving frequency response alone. Sources whose maker never published an output impedance cannot be tested and are marked as such rather than passed.
• Hiss. The source’s own noise, delivered into each pair, staying under 20 dB SPL — roughly where hiss starts intruding in a sealed in-ear. Again, a source with no published noise figure is untested, not clean.

That last distinction matters more than it looks. A source that fails a test is a worse match than one that passes; a source that cannot be tested is neither, and lumping the two together is how most recommendation lists quietly go wrong.

Why the fussiest pair usually decides

Owning a hard-to-drive planar and a sensitive in-ear at the same time is the classic bind, and it is not a power problem. The planar wants volts; the in-ear wants silence and a low output impedance. Plenty of amplifiers give you the first and fail the second, which is why “buy the most powerful one you can afford” is such poor advice for a mixed collection. The hiss calculator and the output-impedance checker work through either half on its own.